HOT WATER CONCRETE TANK TO STORE
SOLAR GENERATED ENERGY
vorgelegt von
Master of Science ‐ M.Sc.
Mohamed Attia Mohamed Abd Elrahman
aus Ägypten
von der Fakultät VI – Planen Bauen Umwelt
der Technischen Universität Berlin
Institut für Bauingenieurwesen
zur Erlangung des akademischen Grades
Doktor der Ingenieurwissenschaften
Dr.‐Ing.
genehmigte Dissertation
Promotionsausschuss:
Vorsitzender: Prof. Dr.‐Ing. Frank U. Vogdt Gutachter: Prof. Dr.‐Ing. Bernd Hillemeier Gutachter: Prof. Dr. rer. nat. Dietmar Stephan Gutachter: Prof. Dr.‐Ing. Alexander Taffe
Tag der wissenschaftlichen Aussprache: 31. März 2014
Berlin 2014
D 83
Acknowledgments iii
Acknowledgements
I would like to express my deepest appreciation to all those who provided me with the possibility to
complete this work with their suggestions, encouragement and advices. First of all, I would like to
express my heartfelt thanks to Prof. Dr.‐Ing. Bernd Hillemeier for his help, valuable time,
encouragement and guidance during all stages of my research work. His outstanding personality as well
as his enthusiasm support, advice, detailed comments and innovative views contributed very much both
to the quality of the research work and to the improvement of my professional skills. I am sincerely
grateful to Prof. Hillemeier, for the confidence he gave me during this study and for the time he has
spent reading and careful review of the manuscript of this thesis. Without his personal interest in the
research work and his great support to overcome all obstacles, this investigation would have not been
materialized.
I would like to express my sincere acknowledgement for the support and help from Prof. Dr. rer.
Nat. Dietmar Stephan, who was abundantly helpful and offered invaluable assistance and provided
me with excellent informational resources and laboratory facilities. I want to thank him for giving
me the chance and space to complete and finish this thesis in his department. I also want to express
him my appreciation for the valuable discussions, beneficial comments and continuous support
during my research.
I am indebted to all the staff and PhD students of the department of building materials and
construction chemistry at TU Berlin for their help and cooperation in my research. It is my pleasure,
however, to mention some of my colleagues: Sameena Kamaruddin, Veronika Märkl and Kai Foth for
their help. I would like to address special thanks to my roommate, Kasra Shafiei, for his support,
advice and for his friendly relationship. Moreover, I wish to express my appreciation to Dr. Roland
Herr for his valuable comments and advices regarding C‐S‐H phase’s transformation. Additionally, I
would like to convey thanks to Dr. Ralf Röben from KIWA for his kindness, friendship and support during
the measurement of porosity and chloride diffusion of concrete.
I also extend my gratitude to German Academic Exchange Service (DAAD) and Egyptian government
for providing financial support for the project during the period of this research. Furthermore, I wish
also to express my thanks for all the great opportunities and professional development I have had at
Berding Beton Firma in Linthe, especially from Mr. Axel Munke and Mrs. Angela Mehlhase for
supporting our experiments.
Finally, I wish to avail myself of this opportunity, and express a never ending sense of gratitude to
my family, my parents, wife, and sons (Omar, Amal and Alaa) for their blessings, understanding,
endless patience, and encouragement at all times.
Acknowledgments iv
Abstract v
Abstract
The solar energy flux reaching the earth equals about 6000 times the current global energy
consumption. Although solar energy is abundant, clean and safe, its supply is intermittent and
irregular. Therefore, a considerable amount of energy should be stored during the day to cover the
demand during the night or from summer to winter times. Hot water storage tank is considered one
of the best technologies for seasonal energy storage because of the high specific heat of water and
the high capacity rate of charging and discharging. Most of these tanks are built of prestressed
concrete with internal lining to prevent the water leakage. The economic studies indicated that the
costs of liner are very high. Moreover, the storing temperature is low (up to 95 °C) which limits
the storing capacity and therefore, the stored energy is used for heating and hot water supply
only. However, to make a practical use of the stored energy such as industrial processes and
steam generation, the storing temperature must be increased above 100 °C such as in the case of
steam accumulator.
The main objective of this work is to study the possibility of optimizing a concrete mixture to be
used in a hot water concrete tank to store solar generated energy at temperatures up to 200 ° C and
pressures up to 15.5 bars. This investigation is divided into three main parts. In the first one, high
density concrete mixtures have been optimized in order to prevent the leakage of water and vapour
through concrete and to ensure high sustainability under hydrothermal conditions. Increasing the
packing density is considered an excellent strategy to get an optimized concrete mix. In this concern,
the Ideal grading curve according to Fuller has been used to achieve the maximum packing density
of the solid materials and to reduce the required binder content. In addition, various cementitious
materials were examined to select the most suitable mixture with high resistance to hydrothermal
attack. Siliceous fillers have been added also to close the gaps between aggregate and fine materials
on one hand and to enhance the stability of C‐S‐H phases under hydrothermal conditions on the
other hand. The second part of this investigation focuses on the effect of autoclaving with 200 °C
and 15.5 bars on concrete properties. Mechanical properties including compressive strength, tensile
strength and rebound number have been measured at normal conditions and after autoclaving with
numerous cycles. In addition, concrete porosity is measured before and after autoclaving for several
cycles. Regarding concrete durability, the main three mechanisms of ingress of gases and liquids
through concrete; permeability, absorption and diffusion, have been measured before and after
autoclaving for several cycles. In the third part, 10 different cement pastes have been prepared and
tested in order to deeply understand the effect of hydrothermal conditions on characteristics and
stability of C‐S‐H phases. In this concern, EDX, TGA and SEM measurements have been used to study
the changes in pastes morphology and properties due to autoclaving for 50 cycles. In addition, the
changes in compressive strength and porosity after hydrothermal treatment have been determined.
Abstract vi
The investigation results showed that the optimized mixes exhibited very low porosity and high
mechanical properties as well as high durability at normal conditions where the grading and particle
size distribution are the main factors influencing the results. However after hydrothermal exposure,
mixes with low C/S ratio showed very stable performance regarding mechanical properties and
durability. The addition of silica‐rich materials such as fly ash, slag and quartz reduces the C/S ratio
of the system and consequently strong product with low porosity and high stability is produced. On
the other hand, mixes with OPC and with high C/S ratio suffered poor durability, high porosity as
well as strength retrogression.
Kurzfassung vii
Kurzfassung
Die auf die Erde treffende Strahlungsenergie der Sonne übertrifft den heutigen
Gesamtenergieverbrauch um die 6000 Fächer. Obwohl die solare Energie unbegrenzt zur Verfügung
steht und sauber und sicher ist, ist ihre Nutzung schwankend und häufig ungewiss. Deshalb sollte
eine beträchtliche Energiemenge tagsüber gespeichert werden, um entsprechend nachts zur
Verfügung zu stehen. Die Speicherung von Energie in heißem Wasser wird als eine der effektivsten
Technologien gesehen, um saisonal Energie zu speichern, weil die spezifische Wärme von Wasser
hoch ist und hohe Beladungs‐ und Entladungsraten erreicht werden können. Um Wasserverluste zu
vermeiden, werden die meisten Speichertanks aus Spannbeton mit einem Inliner hergestellt.
Wirtschaftlichkeitsstudien zeigen, dass die Kosten für den Liner hoch sind. Zudem sind die
Speichertemperaturen verhältnismäßig niedrig (bis zu 95 °C), was die Speicherkapazität wesentlich
einschränkt. Um jedoch die gespeicherte Energie z.B. industriell und bei der Dampferzeugung zu
nutzen, muss die Speichertemperatur deutlich über 100 °C angehoben werden.
Das vorrangige Ziel der vorliegenden Arbeit ist die theoretische und technische Erforschung eines
speziellen Betons für einen Heißwassertank, um solare Energie zu speichern bei Temperaturen bis
zu 200 °C und Drücken bis zu 15.5 bar. Die Forschungsarbeit ist in drei Abschnitte unterteilt.
Zunächst wird ein hochdichter Beton entwickelt, der unter den geschilderten hydrothermalen
Bedingungen zuverlässig wasser‐ und dampfdicht ist. Als spezielle strategische Maßnahme erwies
sich dabei die Erhöhung der Packungsdichte der festen Bestandteile des Betons als besonders
wirksam. Bezüglich dieser Forderung wurde die Idealsieblinie nach Fuller zum Erreichen einer
extrem hohen Packungsdichte und damit zur Reduzierung des Zementleimgehalts angestrebt.
Zusätzlich wurden verschiedene Bindemittelkombinationen untersucht, um die geeignetste
Mischung mit der höchsten Widerstandsfähigkeit gegenüber hydrothermalen Einwirkungen zu
finden. Füller auf Siliziumbasis wurden dem Beton hinzugefügt, um die Lücke innerhalb des
Kornaufbaus zwischen den groben und feinen Materialanteilen zu schießen und die Stabilität der C‐
S‐H Phasen unter hydrothermalen Bedingungen zu erhöhen. Der zweite Teil der Arbeit geht auf die
Analyse der Betoneigenschaften ein, die sich während der Belastung im Autoklaven bei 200 °C und
15.5 bar einstellen. Die mechanischen Eigenschaften wie Druckfestigkeit, Zugfestigkeit und
Rückprallwert wurden bei Normalbedingungen und nach dem Autoklavieren nach verschieden
hohen Zyklen zahlen gemessen. Entsprechend wurden bezüglich der Dauerhaftigkeit des Betons die
drei wesentlichen Mechanismen des Eindringens von Gasen und Flüssigkeiten wie Permeabilität,
Absorption und Diffusion messtechnisch überprüft. In dem dritten Teil der Arbeit wurden 10
verschiedene Zementleime untersucht, um unabhängig von den Einflüssen einer Gesteinskörnung
den Effekt der hydrothermalen Behandlung auf die Charakteristik und die Stabilität der C‐S‐H
Phasen zu erforschen. Dabei wurden die Verfahren EDX, TGA und SEM angewandt, um die
Kurzfassung viii
morphologischen Veränderungen bei den Zementsteinen nach 50 Autoklav Zyklen festzustellen.
Zusätzlich wurden die Veränderungen der Druckfestigkeit und der Porosität gemessen.
Die Versuchsergebnisse zeigen, dass die optimierten Mischungen sich günstig durch eine sehr
niedrige Porosität und hohe mechanische Eigenschaften für die Dauerhaftigkeit auszeichnen. Die
optimierte Kornabstufung wird dabei als der wesentliche Faktor angesehen. Nach der
hydrothermalen Behandlung wird zusätzlich das Calcium/Silizium (C/S) Verhältnis des Systems als
wesentlicher Einflussfaktor auf das Verhalten und die Eigenschaften eines Betons erkannt. Die
Zugabe siliziumreicher Stoffe wie Flugasche, Hüttensand oder Quarzsand reduzieren das C/S
Verhältnis des Systems und führen konsequent zu einem hoch widerstandsfähigen Beton mit
niedriger Porosität bei hoher Zuverlässigkeit. Sie übertreffen in allen ihren Eigenschaften jene
Mischungen deutlich, die ausschließlich aus Portlandzement als Bindemittel hergestellt wurden.
Table of contents ix
Table of contents
Acknowledgements …………………………………………………………………………………….……......….iii
Abstract …………………………………………………………………………………………………………..….……..v
Kurzfassung ……………………………………………………………………………………………………………...vii
Notations and symbols ………………………………………………………………………………….….………xv
1. Introduction ................................................................................................................ 1
1.1 General ..................................................................................................................... 1
1.2 Research Objectives ................................................................................................. 3
1.3 Research strategy ..................................................................................................... 4
1.4 Outline ...................................................................................................................... 4
2. Literature review ......................................................................................................... 9
2.1 General ..................................................................................................................... 9
2.2 Solar energy ............................................................................................................. 9
2.2.1 Introduction ................................................................................................. 9
2.2.2 Concentration of solar power (CSP) .......................................................... 11
2.2.3 Solar Energy storage .................................................................................. 11
2.2.4 Some applications of sensible heat storage systems ................................ 12
2.2.4.1 Central seasonal heat storage .................................................... 12
2.2.4.2 Hot water tank ............................................................................ 13
2.2.4.3 Steam accumulator ...................................................................... 14
2.3 Packing density as a key for concrete mix design .................................................. 17
2.3.1 Introduction ............................................................................................... 17
2.3.2 History of packing density theory .............................................................. 18
2.3.3 The work of Fuller ...................................................................................... 20
2.3.4 State of the art of particle packing modeling ............................................ 23
2.4 Effect of heat on concrete properties .................................................................... 25
2.4.1 Introduction ............................................................................................... 25
2.4.2 Effect of high temperature on properties of cement based materials ..... 26
2.4.3 Explosive thermal spalling ......................................................................... 29
2.4.4 Effect of autoclaving on concrete properties ............................................ 30
Table of contents x
2.4.5 Stability of C‐S‐H phases at hydrothermal conditions ............................... 32
3. Materials and methods ............................................................................................. 39
3.1 Introduction ........................................................................................................... 39
3.2 Materials ................................................................................................................ 39
3.2.1 Aggregates ................................................................................................. 39
3.2.2 Cement ...................................................................................................... 40
3.2.3 Fly ash ........................................................................................................ 41
3.2.4 Silica fume .................................................................................................. 42
3.2.5 Filler ........................................................................................................... 43
3.2.6 Superplasticizer ......................................................................................... 44
3.3 Specimens preparation and curing ........................................................................ 44
3.4 Tests ....................................................................................................................... 45
3.4.1 Fresh concrete properties. ........................................................................ 45
3.4.1.1 Consistency ................................................................................. 45
3.4.1.2 Air content .................................................................................. 46
3.4.1.3 Fresh density ............................................................................... 46
3.4.2 Mechanical properties. .............................................................................. 46
3.4.2.1 Compressive strength ................................................................. 46
3.4.2.2 Splitting tensile strength ............................................................. 46
3.4.2.3 Modulus of elasticity ................................................................... 46
3.4.2.4 Density of hardened concrete .................................................... 47
3.4.2.5 Rebound Hammer ....................................................................... 47
3.4.3 Durability of concrete ................................................................................ 48
3.4.3.1 Water permeability ..................................................................... 48
3.4.3.2 Air permeability .......................................................................... 49
3.4.3.3 Absorption .................................................................................. 50
3.4.3.4 Chloride diffusion test................................................................. 50
3.4.4 Concrete microstructure ........................................................................... 51
3.4.4.1 Effective porosity ........................................................................ 51
3.4.4.2 Helium pycnometry .................................................................... 52
3.4.4.3 Mercury intrusion porosimetry (MIP) ......................................... 52
3.4.4.4 Thermal gravimetric analysis (TGA) ............................................ 53
Table of contents xi
4. Optimizing a high dense concrete mixture................................................................. 55
4.1 Introduction ........................................................................................................... 55
4.2 Maximizing the packing density of solid particles ................................................. 55
4.3 Designing a dense cement matrix .......................................................................... 58
4.3.1 Introduction ............................................................................................... 58
4.3.2 Dense packing of cement matrix ............................................................... 59
4.3.3 Hydration products characteristics ........................................................... 60
4.3.4 Optimizing a dense cement matrix ............................................................ 61
4.3.5 Optimization of water/binder ratio ........................................................... 62
4.4 Densifying the interfacial transition zone .............................................................. 63
4.5 Mix design and mixes composition ........................................................................ 66
4.6 Measuring the packing density .............................................................................. 68
4.7 Measuring the actual packing density αj................................................................ 69
4.8 Results of packing density ...................................................................................... 70
4.8.1 Packing density of fine materials. .............................................................. 70
4.8.2 Packing density of dry concrete mixtures. ................................................ 71
4.8.3 Results of fresh concrete properties ......................................................... 73
4.8.3.1 Air content .................................................................................. 73
4.8.3.2 Workability .................................................................................. 74
4.8.3.3 Density of fresh concrete ............................................................ 75
5. Results and discussion of the optimized concrete properties ........................................ 77
5.1 Introduction ........................................................................................................... 77
5.2 Mechanical properties ........................................................................................... 78
5.2.1 Compressive strength ................................................................................ 78
5.2.2 Splitting tensile strength............................................................................ 79
5.2.3 Modulus of elasticity ................................................................................. 80
5.3 Porosity .................................................................................................................. 82
5.3.1 Porosity measured with helium pycnometry ............................................ 82
5.3.2 Water porosity (effective water porosity). ................................................ 82
5.3.3 Porosity and pore size distribution measured with MIP ........................... 83
5.4 Durability ................................................................................................................ 84
5.4.1 Permeability ............................................................................................... 84
Table of contents xii
5.4.1.1 Water penetration depth ............................................................ 84
5.4.1.2 Air permeability .......................................................................... 85
5.4.2 Absorption (capillary suction) .................................................................... 86
5.4.3 Chloride diffusion ...................................................................................... 88
5.5 Discussion ............................................................................................................... 89
5.5.1 Mechanical properties ............................................................................... 89
5.5.2 Porosity ...................................................................................................... 91
5.5.3 Durability ................................................................................................... 94
5.6 Porosity & mechanical properties relationship ..................................................... 96
5.7 Permeability & capillary porosity relationship ....................................................... 97
5.8 Absorption & capillary porosity relationship ......................................................... 98
5.9 Chloride diffusion & capillary porosity relationship. ............................................. 99
6. Effect of hydrothermal conditions on the properties of densely packed concrete ... 101
6.1 Introduction ......................................................................................................... 101
6.2 Methods ............................................................................................................... 102
6.3 Mechanical properties results.............................................................................. 103
6.3.1 Compressive strength .............................................................................. 103
6.3.2 Rebound number ..................................................................................... 104
6.3.3 Splitting tensile strength.......................................................................... 107
6.4 Porosity measured with MIP ................................................................................ 107
6.5 Durability .............................................................................................................. 109
6.5.1 Permeability ............................................................................................. 109
6.5.1.1 Water penetration depth. ......................................................... 109
6.5.1.2 Air permeability ........................................................................ 110
6.5.2 Absorption (Capillary suction) ................................................................. 111
6.5.3 Chloride diffusion .................................................................................... 113
6.6 Discussion ............................................................................................................. 114
6.6.1 Mechanical properties. ............................................................................ 114
6.6.2 Porosity .................................................................................................... 117
6.6.3 Durability ................................................................................................. 121
6.6.3.1 Permeability .............................................................................. 121
6.6.3.2 Absorption (Capillary suction) .................................................. 122
Table of contents xiii
6.6.3.3 Chloride diffusion ...................................................................... 123
7. Studying the influence of autoclaving on the properties of cement paste................ 125
7.1 General ................................................................................................................. 125
7.2 Mixes and tests .................................................................................................... 125
7.3 Hydration of cement paste .................................................................................. 126
7.3.1 Hydration heat ......................................................................................... 126
7.3.2 Discussion ................................................................................................ 128
7.4 The influence of hydrothermal treatment on cement pastes ............................. 130
7.4.1 Compressive strength .............................................................................. 130
7.4.2 Porosity .................................................................................................... 132
7.4.3 Density ..................................................................................................... 133
7.4.4 Calcium hydroxide content ...................................................................... 134
7.4.5 C‐S‐H phases transformation ................................................................... 135
7.5 Discussion ............................................................................................................. 136
8. Applying the optimized concrete in hot water tank ................................................. 143
8.1 Introduction ......................................................................................................... 143
8.2 Concrete mixture ................................................................................................. 143
8.3 Concrete tank model ............................................................................................ 145
8.4 First experiment ................................................................................................... 145
8.5 Second experiment .............................................................................................. 147
8.6 Future work .......................................................................................................... 149
9. Conclusions and recommendations ......................................................................... 151
9.1 Conclusion ............................................................................................................ 151
9.2 Recommendations ............................................................................................... 154
10. References .............................................................................................................. 157
11. Appendices ............................................................................................................. 171
Table of contents xiv
Notations and Symbols xv
Notations and symbols
Roman
a horizontal axis of the ellipse in the Ideal Fuller curve
aij loosening effect exerted by the particles in size class j on the packing density of the
particles in size class i
A cross section area of the concrete sample (cm2)
b vertical axis of the ellipse in the Ideal Fuller curve
bij wall effect exerted by the particles in class j on the packing of the particles in class i
co chloride concentration of the potassium hydroxide solution (mol.l‐1)
cd chloride concentration at which the colour changes, cd = 0.07 (mol.l‐1)
Cp specific heat of water (J/kg.K)
d diameter of the current sieve (mm)
di diameter of dominant size class i
dj diameter of particle class j
dmin minimum particle size
ds diameter of concrete sample (mm)
D maximum aggregate size (mm)
Dcl migration coefficient of chloride (m2/s)
erf ‐1 inverse error function
Ec modulus of elasticity (MPa)
fc compressive strength of concrete (MPa)
fcm average compressive strength (MPa)
ft splitting tensile strength (MPa)
Ft splitting force (KN)
F Faraday constant, F = 9.649 x 104 (Joule./Volt.mol)
h height of the concrete sample (cm)
Kair air permeability coefficient (cm2)
K compaction index
K absorption water absorption coefficient (kg/m2 hr0.5)
L specimen length in mm
mdry mass of the dried sampled
msat mass of saturated sample
msub mass of sample under water
M mass of the storing material (kg)
Mc mass of concrete sample (kg)
Notations and Symbols xvi
Mp mass of the powder (kg)
Mw mass of water (kg)
n number of size classes in a mixture
pm applied pressure in mercury intrusion porosimetry test (bar)
P applied pressure in air permeability test (N/cm2)
P total per cent passing through a sieve (%)
q gradation ratio (distribution factor)
Q amount of stored heat (Joule)
r radius of the intruded pore in mercury intrusion porosimetry test (nm)
rj volume fraction of size class j
R gas constant, R = 8.315 Joule/(K.mol)
t duration of the chloride diffusion test (s)
T absolute mean temperature of the solutions during the chloride diffusion test (K)
tf the testing period of water absorption (hours)
ta passing time of the air in air permeability test (seconds)
U absolute potential difference in chloride diffusion test (V)
V the volume of concrete sample (m3)
Vf flow volume (cm3)
xo the horizontal value of x axis between D/10 to D (mm)
x1 value where ellipse and the straight line are intersected, equals one‐tenth the
maximum size
xd: mean penetration depth of the chloride ions in each half of the test specimen (m)
y1 vertical value at x1
z valency, for chloride ions, z= 1
Greek
αj actual packing density of each concrete components
αt calculated packing density of the mixture
i virtual packing of size class i
j virtual packing density of size class j
ti calculated virtual packing density of a mixture when size class i is dominant
γc density of hardened concrete (k/m3)
γ surface tension of mercury (N/m)
ε total porosity measured with helium pycnometry (%)
εo free water porosity (%)
η dynamic viscosity of air in (N.s/cm2)
θ contact angle between mercury and the pore walls (degrees)
Notations and Symbols xvii
ρ powder density (kg/m3)
ρb bulk density, calculated by dividing the sample dry mass by the volume (kg/m3)
ρs specific density, determined by using helium pycnometer (kg/m3)
σ splitting tensile strength (MPa)
Abbreviations
αC2SH Alpha dicalcium silicate hydrates
C2S Dicalcium silicates
C3S Tricalcium silicates
C‐S‐H Calcium silicate hydrate gel
C/S Calcium/silicon ratio
CH Calcium hydroxide
CIPM Compaction‐interaction packing model
CPM Compressible packing model
CSP Concentrating solar power
EDX Energy dispersive x‐ray spectroscopy
FA Fly ash
GGBS Ground granulated blast furnace slag
HPC High performance concrete
HSC High strength concrete
ITZ Interfacial transition zone
LPM Linear packing model
M10 Fine fly ash with specific surface area of 6400 cm2/g
M20 Fine fly ash with specific surface area of 6000 cm2/g
MIP Mercury intrusion porosimetry
NSC Normal strength concrete
OPC Ordinary Portland cement
P.D Packing density of each materials
PCE Polycarboxylate‐based superplasticizer
QP Quartz powder
QS Quartz sand
SEM Scanning electron microscopy
SF Silica fume
SP Superplasticizer
TGA Thermogravimetric analysis
UHPC Ultra high performance concrete
w/b Water/binder ratio
w/c Water/cement ratio
Notations and Symbols xviii
Introduction 1
1. Introduction
1.1 General
Nowadays, the rapid growths of population along with the quick developments in all fields lead to a
significant increase in the energy demand. Nevertheless, fossil fuels which are the main energy
resource are limited and subjected to depletion in the next few decades. In addition to the expected
depletion in the near future, their use has a harmful impact on the environment. They are
responsible for the climate changes and environmental pollution; more than 95 % of CO2 emission is
produced by fossil fuel combustion [IEA, 2012]. To cope with these challenging conditions, it is
imperative to develop new energy resources or to enhance the efficiency of the existing resources.
Renewable energy provides an optimum solution for these problems. However, its contribution in
the world energy consumption is very limited (< 1 %). Solar energy can be considered as one of the
most promising alternative energy resource options because it is abundant, clean, safe and
available. The solar energy flow arrived to the earth equals about 6000 times the global energy
consumption [GCEP, 2006]. Nevertheless, the use of this energy is still small compared to the
potential of this resource. Unreliability is the major problem hinders the excessive use of solar
energy. In addition, solar technologies suffer some drawbacks that make them poorly competitive
in the energy market such as high cost, low efficiency and intermittency [Medrano, 2010]. The solar
energy supply is variable during the day and zero at night. On the other hand, the energy demand
also is irregular. So, the energy supply and energy demand, in general, do not match each other.
Therefore, a considerable amount of the produced energy should be stored during the day to cover
the demand at night or from summer to winter times. Solar radiation cannot be stored as such. It
should be transformed into a suitable energy type to be stored. The conversion into thermal energy
is the easiest and the most used method. Solar thermal energy can be stored for long time such as
seasonal energy storage where the stored energy is used only for hot water supply and domestic
heating. Hot water storage tank is considered one of the best technologies for seasonal energy
storage because of the high specific heat of water and the high capacity rate of charging and
discharging. Most of these storage tanks are built of prestressed concrete with internal lining to
prevent the water leakage. The economic studies indicated that the costs of liner represent about
20 % of the total cost of the projects. Recently in Hanover, a concrete tank has been built of dense
high performance concrete without internal lining to store solar energy at temperature up to 95 °C.
However, to make a practical use of the stored energy such as industrial processes and steam
generation, the storing temperature must be increased above 100 °C such as in the case of steam
accumulator. In PS 10 project, in Spain, steam accumulators have been used to store solar thermal
energy at temperature up to 250 °C and pressure of 40 bars [Solucar, 2006]. Nevertheless, the stored
energy covers the energy demands for only one hour with capacity of 50 %. So, improvements are
Introduction 2
required in order to enhance the performance and efficiency of the system, particularly in the
pressurized tank construction materials.
When a concrete wall subjected to hydrothermal cycles, water and vapour try to penetrate the wall.
The penetration rate depends mainly on the temperature and pressure of the water and vapour as
well as on the microstructure, durability and porosity of concrete. In such aggressive conditions,
extremely dense concrete should be optimized to ensure high durability and sustainability. One
possibility of optimizing the mixture is the selection of concrete constituents in such a way that the
packing density of the whole granulometric assemblage is maximized. Proper proportioning of
constituents is important for concrete in order to achieve the homogeneity and uniformity which
cannot be attained without paying attention to the grading and proportions of all components. In
addition to the importance of granulometric optimization, chemical composition of cement paste
has a significant influence on concrete properties. All transport processes depend primarily on the
structure of the hydrated cement paste. During the hydration process, the size and continuity of the
pores control the permeability of the hardening concrete. If the hydration process of cement is too
fast, large amounts of hydration products with capillary pores are generated on the surface of
cement particles at early age and the microstructure is not dense as desired. In contrast, if the
hydration rate is slow, a denser microstructure is formed. The type of cementitious materials has a
crucial role on concrete properties. Portland cement hydration produces about one‐fourth of its
mass of calcium hydroxide (CH), which is associated with greater permeability and lower durability.
The use of pozzolans improves the durability through the pore refinement and the reduction in the
CH content. Concrete durability can be improved significantly by using cements containing blast
furnace slag. These cements, in contrast to ordinary Portland cement (OPC), shows lower
permeability, lower hydration heat, lower effective alkali content, and lower steel corrosion. On the
other hand, the transition zone between cement and aggregates is considered the weakest link in
concrete under mechanical action and it is also the locus of micro‐cracking. It plays a critical role
in controlling the bulk transport properties. The incorporation of mineral admixture significantly
enhances the transition zone properties from several aspects depending on its reactivity and
particle size.
When exposed to elevated temperature, concrete chemical and physical characteristics are severely
changed, which affect its overall performance. The most important influences are the significant
increase of porosity, moisture content alteration, pore pressure change, compressive strength
retrogression (strength loss) and thermal cracking. Concrete elements can be implemented in many
applications in which different types of heat exposure can be expected. It can subject to pure heat as
in the case of fire or to hydrothermal conditions where it subjected to both heat and saturated vapour
Introduction 3
pressure. The behaviour of concrete under hydrothermal conditions (autoclaving) is complex
because it exposed to repeated cycles of heating and cooling as well as repeated cycles of
vaporization and condensation (autoclaving cycles). The chemistry of autoclaving is differing from
that at normal conditions or at heat only and it depends mainly on the chemical composition of the
bulk mixture. The dominant process on pure heat exposure of concrete is the loss of various forms
of water (free, adsorbed and chemically bound). However, the dominant process in the autoclaving
process is hydrothermal chemical reactions and phases transformation which may result in stronger
or weaker products depending on the C/S ratio of the bulk [Khoury, 2000]. When C‐S‐H gel of OPC is
subjected to autoclaving with temperature higher than 110 °C in the absence of reactive silica, it is
quickly converted to lime‐rich phases with high crystallinity [Hewlett, 2003; Mindess, 2003]. Phases
such as αC2SH, hillebrandite and ‐tricalcium silicate are the most stable phases in the system with
high lime content. The lime‐rich phases formation is accompanied by an increase in the density
which causes shrinkage of the solid products and therefore the porosity increases and the strength
is markedly decreased. The loss of strength due to elevated temperature exposure is commonly
known as strength retrogression. With sufficient addition of silica, pozzolanic reaction is accelerated,
portlandite is consumed, C/S is considerably reduced and the formation of lime‐rich C‐S‐H phases is
prevented [Nelson, 1990; Glasser, 2003]. Instead, numerous silica‐rich phases such as gyrolite,
xonotlite and 1.1 nm tobermorite are formed, which lead to high strength and low permeability.
1.2 Research Objectives
Worldwide, several hot water concrete tanks have been constructed to store solar thermal energy.
Most of these tanks use an internal lining to ensure leak‐tightness. The working temperature is
limited below the boiling point of water on most tanks. However, for efficient energy usage in
industrial applications using steam generation, the storing temperature must be increased above
100 °C while water and steam become pressurized. The main objective of this project is to study the
possibility of optimizing a concrete mixture to be used in a hot water concrete tank to store solar
generated energy at a temperature of 200 °C and a pressure of 15.5 bars without internal lining. In
the targeted tank, the leakage of water and vapour is prevented by implementing a very dense high
performance concrete. The optimized concrete should exhibited high efficiency and stability after
exposing to various autoclaving cycles. An important subject in this respect is the stability of C‐S‐H
phases after hydrothermal exposure with several cycles. Many factors influence the behavior of
concrete under these hydrothermal conditions. Regarding transport properties through the
optimized concrete, the mineralogical properties of concrete constituents are of more concern.
However, chemical composition of the concrete mixture is considered the basic parameter with high
impact on the stability of C‐S‐H phases.
Introduction 4
1.3 Research strategy
In order to achieve the objectives of this investigation, the experimental work is divided into three
main parts. In the first part, a high density concrete mixture has been optimized in order to prevent
the leakage of gases and liquids through concrete and to ensure high sustainability under
hydrothermal conditions. Increasing the packing density is considered an excellent strategy to get an
optimized concrete mix. In this concern, the Ideal grading curve according to Fuller has been used to
achieve the maximum packing density of the solid materials and to reduce the required binder
content. In addition, various cementitious materials were examined to select the most suitable
mixture with high resistance to hydrothermal attack. Furthermore, siliceous fillers have been added
to close the gaps between aggregate and fine materials on one hand and to enhance the stability of
C‐S‐H phases under hydrothermal conditions on the other hand. Moreover, Rene LCPC program
based on compressible packing model has been used to compare the effect of grading and
proportions of concrete components on the packing density of the mixture. The second part of this
investigation focuses on the effect of autoclaving with 200 °C and 15.5 bars on concrete properties.
Mechanical properties including compressive strength, tensile strength and rebound number have
been measured at normal conditions and after autoclaving with numerous cycles. In addition,
concrete porosity is measured before and after autoclaving for several cycles. Regarding concrete
durability, the main three mechanisms of ingress of gases and liquids through concrete;
permeability, absorption and diffusion, have been measured before and after autoclaving for several
cycles. In the third part, 10 different cement pastes have been prepared and tested in order to
deeply understand the effect of hydrothermal conditions on characteristics and stability of C‐S‐H
phases. In this concern, EDX, TGA and SEM measurements have been used to study the changes in
pastes morphology and properties due to autoclaving for 50 cycles. In addition, compressive
strength and porosity after hydrothermal treatment have been determined.
1.4 Outline
The research work presented in this investigation covers several fields, actually different but
nevertheless closely related to the topic of this thesis. Two main topics represent the main body of
this thesis. First, optimization of dense concrete mixture (Chapter 3, 4 and 5), second; studying the
behaviour of cement based materials after hydrothermal exposure (Chapter 6 and 7). This PhD
thesis consists of 9 Chapters, and its structure is given in Figure 1.1.
In the first chapter (Introduction), basic facts are given on solar energy, optimization of concrete
mixture and behavior of concrete under hydrothermal treatment, on the objectives of this
investigation and on research methodology.
Chapter 2 is a literature survey and divided into three main parts. In the first part, a literature
overview on solar energy technologies is given. In this part, a description of different methods of
Introduction 5
concentrating solar energy is introduced. This part also presented the modern technologies of solar
energy storage techniques either for seasonal terms for domestic heating and hot water supply or
for short terms for electricity and power generation. The second part of this chapter presented a
general historical background of the dense packing. In addition, some important formulas of
particles grading which assumed to achieve the maximum packing density are presented. Several
packing models to predict the packing density of concrete mixtures are also given. The last part of
this chapter points out the influence of elevated temperature on concrete properties. In addition,
the effect of hydrothermal treatment on concrete characteristics and stability of different C‐S‐H
phases are also discussed.
Chapter 3 describes the properties of the used materials and test methods. Chemical properties of
the used materials as received from the manufactures are given in this chapter. Physical properties
of aggregates and cementitious materials which have been determined in the laboratory are
introduced. In addition, particle size distribution of all materials measured either by sieve analysis
(aggregate) or by laser granulometry is given. In addition, a description of the experimental tests is
given. In this concern, measurement procedures of properties of fresh and hardened concrete
according to the standards are demonstrated.
Chapter 4 focuses on optimizing a high density concrete mixture. The mixture optimization is based
on three fundamental mechanisms: enhancing the packing density of solid particles, designing of
dense cement matrix, and densifying the interfacial transition zone. Enhancing the packing density
of solid particles is ensured by applying the Ideal Fuller curve for proportioning aggregates and fines.
However, the designing of dense cement matrix and enhancing the properties of transition zone are
achieved by incorporation of several fine materials and by adjusting the water/binder ratio. Twenty
three mixes were prepared and tested. At the end of this chapter the results of packing density
measurement and properties of fresh concrete are given.
Chapter 5 contains the results and discussions of the experimental investigations. These
experiments are conducted to evaluate the mechanical properties and durability of the optimized
mixes. Mechanical properties including compressive strength, tensile strength and modulus of
elasticity are measured. However for durability, permeability, capillary suction and chloride diffusion
are determined. In addition, the results of porosity measured with three different mediums; water,
helium and mercury are presented. At the end, relationships between mechanical properties and
durability with porosity are drawn in order to declare the effect of porosity on concrete properties.
In chapter 6 the results of the effect of hydrothermal conditions on concrete properties are
presented. The experiments aim to highlight the effect of autoclaving with 200 °C and 15.5 bars for
various cycles on the mechanical properties and durability of concrete. These results demonstrate
the suitability and sustainability of concrete mixtures to be used in the targeted conditions. In
addition to durability and mechanical properties, a comparison between concrete porosity and pore
Introduction 6
size distribution before and after autoclaving with 50 cycles are provided by using mercury intrusion
porosimetry.
In chapter 7, the experimental test results of 10 different cement pastes are given. The aim of this
experimental part is to study the stability and characteristics of C‐S‐H phases after hydrothermal
exposure. Strength retrogression and permeability increase due to phase’s transformation are the
main focus of this chapter. Therefore, compressive strength and porosity tests of different cement
pastes are performed. In addition, in order to deeply understand the effect of hydrothermal
treatment on the stability and transformation of different C‐S‐H phases SEM, EDX, TGA
measurements have been implemented.
Chapter 8 presents the results of the preliminary experiments of hot water concrete tank model
made of the optimized concrete to store hot water and vapor at temperature above 100 °C.
Chapter 9 summarizes the achievements and final conclusions of this study. Based on the results of
this research project, recommendations and ideas for future research are also provided.
Introduction 7
Figure 1.1: Outline of the thesis
General
Concrete mixture
optimization
Effect of hydrothermal
conditions of cement
based materials
Chapter 4: Optimizing a high dense concrete mixture
Chapter 5: Results and discussion of the optimized
concrete properties
Chapter 1: Introduction
Chapter 2: Literature review
Chapter 3: Materials and Methods
Chapter 6: Effect of hydrothermal conditions on the
properties of densely packed concrete
Chapter 7: Studying the influence of autoclaving on
the properties of cement paste
Chapter 8: Applying the optimized concrete in
hot water concrete
Chapter 9: Conclusions and recommendations
Applications
Introduction 8
Literature review 9
2. Literature review
2.1 General
This chapter gives a literature survey on three different main themes which are required as
foundations of this research work. The first part of this chapter, solar energy storage, discusses the
new technologies in solar energy applications. It points out the different methods of concentrating
sun radiation. In addition, it refers to various storing systems using hot water and steam as working
medium, either with low temperature (< 100 °C) or with high temperature (> 100 °C). In the second
part of this chapter, a historical background about packing density is presented. It includes a
demonstration of the ideal grading curves and formulas which can be applied to achieve the
maximum dense packing of concrete mixtures. Moreover, it introduces some packing density
models which can be used to predict the maximum packing density of any concrete mixture. In the
last part, the effect of high temperature exposure on concrete mechanical properties and durability
is discussed. In this section, three topics are of main interest: effect of pure heat, explosive spalling
and hydrothermal conditions up to 200 °C. At the end of this part, a literature review about C‐S‐H
phases and their stability and properties after hydrothermal exposure are given.
2.2 Solar energy
2.2.1 Introduction
Fast worldwide, economic development leads to a quickly increase in energy demand. In recent
years, many attentions have been paid to renewable energy because of the environmental harmful
effects of the conventional energy resources in addition to the expected depletion of them in the
next few decades. Nevertheless, the contribution of the renewable resources in the world energy
consumption is very limited (< 1 %) as it is obvious in Figure 2.1. Solar energy can be considered as
one of the most promising alternative energy resource options because it is abundant, clean, safe
and available. The sun energy potential is the greatest energy resource on the earth and by far
exceeds those of other renewable energy sources [Philibert, 2011]. The solar energy flow arrived to
the earth equals about 6000 times the current total global energy consumption [GCEP, 2006].
Despite the high abundance of solar energy, its use is still small compared to the potential of this
resource. Solar technologies suffer from some drawbacks that make them poorly competitive in the
energy market such as high cost, low efficiency and intermittency [Medrano, 2010]. Unreliability is
the major problem hinders the excessive use of solar energy. From a scientific and technological
viewpoint, the great challenge is to find a new solution for solar energy systems to become less
intermittent, more efficient and reliable.
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Literature review 11
2.2.2 Concentration of solar power (CSP)
Concentrating solar thermal power provides a possibility for using sun energy to generate electricity
with producing very low levels of greenhouse gas [IEA, 2010]. Thus, it has strong benefits to be the
new technology for mitigating global warming. It is a power generation technology by using lenses
or mirrors to concentrate a large area of sun rays onto a small area, either point or line. Most
systems use glass mirrors with flat or curved surfaces because of their high reactivity [Trieb, 2009].
The concentrated heat is absorbed on the receiver which is designed to reduce the heat losses. The
collected energy is used to heat a fluid flowing through the receiver and to produce a steam with
high pressure [IRENA, 2012]. The produced steam drives a turbine and generates energy as in the
traditional power plants. The heat transfer fluids could be air, water, oil or molten salt [Trieb, 2005].
There are four main technologies for concentrating solar rays: parabolic trough, solar tower, linear
fresnel and parabolic dish as shown in Figure 2.2.
2.2.3 Solar Energy storage
Although the solar energy is abundant, clean and safe, the supply of this energy is intermittent and
irregular. The solar energy supply is variable during the day and zero at night. On the other hand,
the energy demand is also irregular. So, the energy supply and energy demand, in general, do not
match each other. Therefore, a considerable amount of the produced energy should be stored
during the day to cover the demand at night. The thermal energy storage is essential for solar
energy system in order to enhance the reliability, efficiency and competitiveness of this system. The
need for solar energy storage could be linked to the following causes:
1. To adjust the mismatch between energy supply and demand.
2. To provide a continuous and reliable energy source.
3. To reduce the greenhouse gas emission by substituting fossil fuels with clean energy.
4. To compensate the times of fluctuation in solar energy systems.
5. To serve as a reservoir to store the excess energy (buffering) when the energy supply higher
than energy demand.
Solar radiation cannot be stored as such; it should be transformed into a suitable energy type to be
stored. The conversion into thermal energy is the easiest and the most used method. Thermal
energy storage is one of the advantages of concentration of solar power (CSP) compared to other
renewable energy technologies such as photovoltaic or wind [Trieb, 2009]. Many parameters affect
the storage system efficiency such as maximum working temperature and specific heat of the
storing material, storage capacity, chemical and mechanical stability, compatibility between storing
material and transfer fluid, thermal losses and ease of control [GCEP, 2006]. Mainly, there are three
methods for thermal energy storage: sensible heat, phases change materials and chemical reactions.
Literature review 12
2.2.4 Some applications of sensible heat storage systems
In sensible heat storage method, the storage is based on increasing or reducing the temperature of
the material without changing its phase during the process. The storage capacity depends upon the
heat capacity of the medium and the temperature increase. Other parameters are significant for
sensible heat storage such as diffusivity, working temperature, thermal conductivity and heat loss
per unit volume. A sensible heating system consists mainly of the container, inlet/outlet device and
storage medium [GCEP, 2006]. The container (tank) should be able to resist the loads, temperature
differences and also to prevent thermal losses. Several materials could be used as storage medium
such as solids (rocks, concrete…) or liquid (water, oil…). Because of its very low heat capacity, gases
cannot be used for cold or hot storage [Paksoy, 2007]. Sensible heat technology is cheap compared
to other mechanisms, but the energy density is low. The stored energy can be calculated according
to the following formula:
Q= M.Cp. T (1.1)
Where Q is the amount of stored heat (J), M is the mass of the storing material (kg), Cp is the specific
heat (J/kg.K) and T is the temperature range of operation (K).
2.2.4.1 Central seasonal heat storage
Domestic water heating represents about 30 % of the total energy consumed by buildings [IEA,
2010]. The primary function of this system is the use of solar collector to capture the sun rays and
transfer it directly to heat. The heat is transferred from the collectors by using thermal transfer fluid,
which carries the heat for direct use or to heat storage (sensible heat storage medium). The heat
storage is charged when the solar collectors gather solar heat more than the required by the
network. During the summer, charging takes place, whereas in the winter the stored energy is used
for domestic hot water and space heating. In addition, a heat pump is integrated in the system in
order to achieve high efficiency [Schmidt, 2006]. The long term (seasonal) heat storage can provide
heat up to about 70 % of the annual heating demand [Novo, 2010]. In all types of seasonal heat
storage, the maximum temperature is limited below 100 °C. Four main technologies are developed
and used for storing solar thermal energy as can be seen in Figure 2.3.
Aquifer thermal energy storage. Borehole thermal energy storage.
Pit storage. Hot water tank
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Literature review 17
2.3 Packing density as a key for concrete mix design
2.3.1 Introduction
In recent years, progress in science and technology in the field of construction materials and usage
of new materials have resulted in the use of reinforced concrete in special structures, which need
high durability and high resistance to chemical attack such as cooling towers of power plants,
sewage systems, nuclear power containments, etc… In these aggressive conditions, the transport of
contaminants through concrete is of more concerns. Movement of fluids and gases in concrete
occurs through the network of continuous pores, which exist in cement matrix as well as in the
interfacial region with the aggregate. Concrete is a heterogeneous material with complex
microstructure consists mainly of several components and phases with various properties.
Aggregate occupies between 60 ‐ 80 % of the total volume of concrete [Rached, 2009]. It represents
the main body of concrete. Therefore, proper selection of aggregate type and content directly
influence the main properties of concrete. On the other hand, cement paste takes around 15 ‐ 30 %
of the whole volume. It fills the voids between the aggregate, binds them together and renders the
fluidity of fresh concrete. Although increasing cement paste has a positive influence on the properties
of fresh concrete, it has some negative effects on the hardened state, especially in the early ages. It is
responsible for some of the problems in concrete such as shrinkage and hydration heat in addition to
high porosity.
Optimization of a concrete mixture is most important and complicated as there are a variety of
variables influencing the results. One possibility of optimizing the mixture is the selection of
concrete constituents in such a way that the packing density of the whole granulometric assemblage
is maximized. Granular materials can be packed together in several arrangements, from dense
packing to loose packing [Alexander, 2005]. The type of arrangement relies mainly on particle size
distribution, particles shape and particles interactions. If a high volume of solid materials can be
packed efficiently in a certain volume, then the voids in the mixture are minimized, and thereby the
required paste to fill this void is significantly reduced. As a consequence, more paste is available to
maintain the required workability and increasing the strength [Grutzeck, 1993]. In addition, mixes
with high density exhibited lower segregation and bleeding [Quiroga, 2003]. For hardened concrete,
the hydration heat, creep and shrinkage are significantly reduced due to minimizing cement content.
An additional benefit of maximizing packing density is to block and lengthen the access path of
contaminants into concrete.
The packing density can be defined as the ratio of fraction volume occupied by the solids to the
volume of the surrounding container. Goltermann defined the aggregate packing degree as the ratio
Literatur
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The prin
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les, 2005].
f randomly
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Literature review 19
The optimum packing density of the system could be attained only if spheres with smaller sizes are
added to the assemblage. The small size spheres can fill the voids between the large spheres, and
thereby the packing density is significantly increased. In 1961, McGeary reported that it is possible
to achieve a packing density of 95.1 using four different sizes of spheres which have diameter ratios
of 1, 7, 38 and 316 with fraction volumes of 6.1, 10.2, 23 and 60.7 % respectively. However, the
maximum density of infinite differences in sizes can be attained is 97.5 % [McGeary, 1961].
For concrete, the situation is more complex since the system composed of various particle sizes with
different shapes. Effective packing can be attained by selecting a proper proportion and size of small
particles to fill in the voids between the bigger particles. The important effects of aggregate grading
on the properties of concrete have been emphasized in very early reports. Several early studies
were concentrated on solving the problem of establishing the ideal grading curves to achieve the
maximum packing density by combining fine and coarse aggregate. In 1892, Rene Feret studied the
relationship between the packing of concrete components and the properties of concrete
[Newlands, 2001]. He concluded that the maximum strength can be achieved when the porosity of
the mixture is minimal [Hüsken, 2008]. Fuller (1907) was one of the first researchers deeply studied
the maximum density of aggregate and a mixture of aggregate and cement [Fuller, 1907]. After a lot
of experimental works, he reported that the best grading of aggregate to get the maximum density
is a parabolic shape. Both Feret and Fuller confirmed that concrete properties can be significantly
improved by using continuous grading [Hüsken, 2008]. In 1923, Talbot developed the well‐known
equation:
P (2.2)
Where P is the total percent passing through a sieve, d is the diameter of the current sieve, D is the
maximum aggregate size and q is the gradation ratio [Rached, 2009]. The maximum packing density
can be achieved when q = 0.5, which is close to the Fuller curve [Powers, 1968; Brouwers, 2005;
Fennis‐Huijben, 2010], but the resulting concrete is harsh and unsuitable. In 1930, Andreasen and
Andersen tried to improve the Fuller curve. They suggested using the exponent q in the range of
0.33 ‐ 0.5 because fine particles are not able to pack similar to bigger particles [Andreasen, 1930;
Zheng, 1990; Hunger, 2010]. The factor q has to be experimentally determined and it depends upon
the properties of particles, considering the fact that no theoretical determination of this factor has
been attempted [Zheng, 1990]. For angular particles, low q is preferred in order to increase the fine
materials to fill the voids between coarse particles, to keep the workability at the required level and
to enhance the packing of the system [Fennis‐Huijben, 2010]. Hummel found that Fuller curve (q =
0.5) does not give the maximum density at any case. He recommended q = 0.3 for angular
aggregate, and 0.4 for round aggregate in order to get the optimum packing density [Hunger, 2010].
Literature review 20
Shilston suggested that taking q = 0.45 provides the optimum packing density [Shilstone, 1990;
Rached, 2009]. However, according to equation 2.2, infinite small particles are required to achieve
the maximum theoretical packing density [Zheng, 1990]. Alexander and Mindess also pointed out
the important role of including the overall grading of all mixture components in the packing theory
in order to achieve the high performance characteristics [Alexander, 2005]. Funk and Dinger stated
that any size distribution must have minimum particle size (dmin). The ideal particle size distribution
depends not only on the maximum aggregate size, but also on the minimum particle size as can be
seen in equation 2.3 [Zheng, 1990; Hüsken, 2008; Hunger, 2010].
P (2.3)
Higher values of q (> 0.5) lead to coarse mixtures with low fine material content. However lower
values (< 0.25) lead to mixture with high fine material content which considerably reduces the
packing density [He, 2010]. Generally, in order to achieve the maximum packing and keep the
workability at an acceptable level, it is suggested to take q = 0.37 [Fennis‐Huijben, 2010; Vogt, 2010].
For self‐compacting, it is recommended to take q in the range of 0.22 – 0.25 in order to achieve the
required workability [Hüsken, 2008].
2.3.3 The work of Fuller
The American William Fuller can be considered as the father of granulometric optimization in
concrete technology [Puntke, 1990]. At the beginning of the last century, he studied grading analysis
for a wide variety of aggregate types and mixtures for the sake of deriving the optimum grading that
achieves the maximum packing density [Lees, 1967]. In his famous book, The laws of proportioning
concrete, he mentioned that, in 1901 it was found that the best density of aggregate can be attained
when the particle size distribution of aggregate is continuously graded and the grading curve takes a
parabolic shape when plotted in natural scale as can be seen in Figure 2.9. Despite of its historical
value, Fuller curve is used as the base for proportioning of aggregate in many national concrete
standards [Vogt, 2010]. This curve is still known until now as Fuller parabola and can be applied for
calculating the optimum grading of aggregate only as he himself mentioned later [Fuller, 1907]. The
reason for that lies on the fact that the mixture of aggregate which gives the maximum density in
the dry state does not necessarily achieve the greatest density when combined with cement and
water. This is because the low void content between the aggregate particles prevents the cement
and water to fit in perfectly [Fuller, 1907; Richardson, 2005; Rached, 2009].
In 1903, Fuller began an intensive work to achieve the greatest packing density for a mixture of
aggregate and fine materials. He reported that the best curve was obtained by trial mixes without
Literature review 21
referring to the mathematical basis of the curve. It was concluded from this work that there is a
certain ideal grading curve to all solid materials, composed basically of an ellipse at the lower part,
and merging into a straight line tangent to the elliptical part [Powers, 1968]. He stated that “The
curve which gave the best result when using a graded coarse aggregate with the cement was found
to be one resembling a parabola in appearance, but, more strictly, consisting of a curve having for
the lower portion the form of an ellipse, and above this a straight line running to 100 % on the
maximum diameter of the stone”. After finding the best grading, equations were fitted to these
curves. The ellipse begins from 0.0029 inch (sieve No 200) and runs to a value of x equal to one‐tenth
of the maximum grain size. At this point, the straight line begins and continues to y = 100 percent and
x = D (where D is the maximum grain size of aggregate) as can be seen in Figure 2.10. The equation
covering this curve was divided into two parts:
For the elliptical part:
71 (2.3)
For the straight line part:
100
(2.4)
Where a and b are the axis of the ellipse and their values depend mainly on the shape of the particles
and the maximum aggregate size and x0 = D/10 to D, y1 = yel at D/10 and x1 = D/10 [Puntke, 1990].
The linear scale for the Ideal curve is not satisfactory because the lines in the small size zone are too
crowded for defining. In 1990, Puntke referred to all these notes and redraw the Ideal Fuller curve in
a semi‐logarithmic scale for the sake of simplicity as can be seen in Figure 2.11 [Puntke, 1990]. The
Ideal Fuller curve has been used for designing concrete mixes for some applications, particularly
those need high density and high resistance to acid attack. For example, in 2000, the highest cooling
tower in the world (200 m, Niederaußem, Germany) has been constructed of acid resistant
concrete. The used concrete has been designed on the basis of the Ideal Fuller curve. Because of its
high density and resistance to acid attack, the concrete did not need any additional protective layer
[Busch, 1999; Hüttl, 2000]. Furthermore, it showed very low chloride diffusion as well as high frost
resistance without air entraining agents. In addition to the technical benefits, some economic
benefits were gained by reducing the cement content to about 50 % compared to conventional high
performance concrete with similar strength.
Literatur
Figure 2According
Figure 2According
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Passing %
re review
2.9: Fuller pag to [Fuller, 19
2.10: Ideal gg to [Puntke, 1
0
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22
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Literature review 23
Figure 2.11: Ideal Fuller grading curve for aggregate and fine materials in logarithmic scale According to [Fuller, 1907]
Many authors did not differentiate between Fuller parabola and Ideal Fuller curve [Powers, 1968;
Newlands, 2001; Mindess, 2003; Alexander, 2005; Brouwers, 2005; Brandt, 2009; Rached, 2009;
Hunger, 2010]. They did not consider the elliptical section of the Ideal Fuller curve and assumed
equation 2.2 as synonymous with this curve. Furthermore, they deal with Fuller parabola as the
optimum grading curve for aggregate and binder mixture. This assumption tends to produce lean
mixes with lower fines content [Lees, 1967]. Therefore, the use of this curve in concrete mix design
is limited due to the poor workability and probability of segregation of the produced concrete.
However, compared to Fuller parabola, the Ideal grading curve has higher content of fines and lower
coarse aggregate content as can be seen in Figure 2.11. For example, for mixture with maximum size
of 16 mm, about 8.8 % of solid materials pass from the sieve size 0.125 mm according to Fuller
parabola, whereas according to Ideal Fuller curve, 14.9 % passes from the same sieve size.
2.3.4 State of the art of particle packing modeling
In the previous section, some theories about the appropriate selection of concrete components in
order to get the ideal grading of particles have been mentioned and discussed. However in this
section, theoretical particle packing models to estimate the packing density ratio of solid
combination will be presented. Packing model provides an important tool to design concrete
mixture with minimum cement and water contents and with maximum solids content [Jones, 2002].
One of the big problems for engineers is to achieve high packing density and ensure the desirable
workability. By developing packing models, it is possible to select the mixture which provides the
maximum packing density and minimizes the remaining voids. The particle packing models explain
100
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10
20
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50
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0.0001 0.001 0.01 0.1 1
Passing %
Sieve size (d/D)
Literature review 24
the way of which the particles are packed together based on mathematical hypothesis. Most of
these models calculate the minimum voids ratio on the basis of the particle geometry and size
distribution.
In 1929, Furnas developed a model for predicting the packing density of two monosized particles in
two cases; the small particles are the dominant or the large particles are the dominant [Fennis‐
Huijben, 2010]. Two years later, he developed a method to estimate the maximum packing density
of multi‐size particles taking into account the effect of interaction between particle groups [Furnas,
1931]. The main idea of his approach is that the maximum packing density will be achieved if the
small size particles fill the voids between the large particles [Vogt, 2010]. Ben Aiim and Goff
modified the Furnace model by implementing the wall effect into the model [Andersen, 1993; Nehdi,
1998; Fennis‐Huijben, 2010]. In 1976, Toufar et al developed a model based on Furnace equations.
Afterwards, Toufar model was modified by implementing diameter and packing density of each
material to predict the packing density of the mixture [Jones, 2002]. In 1999, Dewar developed a
packing model based on the particle size distribution. It can calculate the theoretical packing density
of a concrete mixture by knowing voids ratio and the mean size of each single constituent [Dewar,
2002]. Stoval et al developed linear packing model (LPM) based on discretely sized particles [Vogt,
2010]. These models take into account the wall effect, particle shape and effect of fine particles on
the packing of larger particles. With some modification on LPM, De Larrard developed compressible
packing model (CPM) in 1999. This model is based on two new concepts: virtual packing density and
compaction index [Larrard, 1999]. Jones et al made a comparison of four packing models (modified
Toufar, Dewar, LPM and CPM models) by making some laboratory experiments. It is found that all
models give similar output and suggest similar materials combination to achieve the minimum
porosity [Jones, 2002]. However, in the conclusion he mentioned that much work is still required in
the development of modeling, in particular, in the way in which the particle shape and mean particle
sizes are considered. Fennis also studied several models and concluded that the compressible
packing model is the most accurate model with the highest ability for modification to cover various
interactions. She developed compaction‐interaction packing model taking into account the influence
of inter‐particle forces in addition to wall effect and loosening effect [Fennis‐Huijben, 2010]. In this
model, packing of fine materials and binders should be experimentally determined and included as
inputs. It is concluded that no direct relation between maximum packing density and either
compressive strength or hydration heat of cement was found. A good relation was found between
compressive strength and the distance between cement particles. It was mentioned also that, more
than 50 % of cement can be saved and about 25 % of CO2 emission can be reduced while the
concrete is still achieve the requirements for the appropriate use by applying packing density
models.
Literature review 25
Over the last few years, a number of computer programs based on the packing equations and
models have been developed. The development of computer analysis and simulation provides a
powerful tool for modeling the packing of particles. These programs give the engineers the ability to
determine the optimum combination of concrete constituents that ensures a maximum packing
density and minimum voids. For example, EMMA is commercial computer software based on the
Andreassen equation for packing density, and can be used for concrete mix design
(www.concrete.elkem.com). In addition, MixSim (www.mixsim.net) is a mix design program based
on Dewar model [Dewar, 2002]. On the other hand, Rene‐LCPC is software based on CPM and can
be used to determine the maximum packing density (lcpc.fr). Similarly, Europack is a software based
on the modified Toufar model to estimate the packing density of dry mixtures [Alexander, 2005;
Rached, 2009].
2.4 Effect of heat on concrete properties
2.4.1 Introduction
Compared to other construction materials, concrete can be considered one of the best materials
regarding resistance to elevated temperature. It is incombustible and has low thermal diffusivity. It
has good fire resistance and provides a protection layer for reinforcement. Various structures can be
subjected to elevated temperature, which must be taken into consideration when designing and
detailing of reinforced concrete structures. Tunnels, high rise building, underground parks, nuclear
power plants and jet aircraft engine blasts are examples of such structures where the probability of
elevated temperature exposure is high and very dangerous. Studying the behaviour of concrete at
high temperature is very complex not only because it is composed of several constituents with
different properties, but also because the porosity and moisture content play important roles in the
concrete performance at these aggressive conditions. At high temperature, chemical and physical
characteristics of concrete are severely changed, which affect the overall properties of concrete.
Chemical changes can be beneficial (further hydration of unhydrated cement particles) or
detrimental (decomposition of hydrated cement paste), and it relates to the cement paste and
aggregate. However, the physical effects are related to dimension compatibility between aggregate
materials and cement paste.
The moisture content of concrete affects its performance at high temperature dramatically. At high
temperature (> 100 °C), water changes its state and as a result some influences take place at certain
temperatures. The capillary and gel water are evaporated at temperature of 100 ‐ 150 °C. However,
above 250 °C, the chemically bound water starts to evaporate and the compressive strength starts
to decrease. Dehydration of calcium hydroxide takes place at approximately 450 °C. At higher
Literature review 26
temperature, the C‐S‐H begins to decompose and significant decrease in compressive strength
occurs [Rashad, 2012]. Concrete can be implemented in many applications in which different types
of heat exposure can be expected. It can subject to pure heat as in the case of fire. However,
hydrothermal conditions are another case in which the concrete can be subjected to both heat and
saturated vapour pressure such as in nuclear power plants and water tanks for storing thermal energy.
2.4.2 Effect of high temperature on properties of cement based materials
Under high temperature exposure, heat is transferred by convection and conduction through the
concrete, and the free water starts to evaporate depending on the working temperature. Concrete
durability and mechanical properties are markedly changed due to deterioration of aggregate,
decomposition of hydrated cement paste and thermal incompatibility between paste and aggregate
which resulted in microcracking and stress concentration [Mindess, 2003]. The literature search
results on the behaviour of concrete at elevated temperature give widely varying results [Neville,
2004]. As Neville reported, "globally valid generalizations are difficult" [Neville, 2004]. This can be
attributed to the differences in moisture conditions of concrete, in the exposure period, in heating
rate and in concrete compositions.
In the literature, the behaviour of normal strength concrete under elevated temperature is well
documented. However, limited researches are available about the performance of other types of
concrete, in particular, when mineral admixtures are incorporated. Dias et al. studied the
mechanical properties of hardened cement paste exposed to high temperature up to 700 °C. A
decrease in compressive strength was observed at temperature around 100 °C. He attributed that to
the swelling of physically bound water layers. The original strength regained and maintained with
increasing the temperature to 300 °C. The regaining of strength could be due to the relief of the
build‐up pressure and the increased Van der Waals forces which result from the movements of
cement gel layers closer to each other. He suggested 300 °C as the critical temperature point with
respect to strength loss for unsealed Portland cement concrete [Dias, 1990]. Above this
temperature, rapid increase of porosity and micro‐cracking are occurring which leads to degradation
of mechanical properties. Another investigation has been carried out by Seleem et al. [Seleem,
2011]. He found that the compressive strength of concrete incorporating pozzolanic materials is
increased after elevated temperature exposure up to 200 °C. He attributed that to evaporation of
free water which results in an increase in friction between failure planes. In addition, at this level of
temperature, self‐autoclaving process is enhanced which accelerates the rate of cement hydration and
pozzolanic reaction.
Literatur
Galle an
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Figure 2 [Poon, 20
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2001]. The co
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et al. [Fara
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which are dif
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2001] carried
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ement paste
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FA and GGBS
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nd 95 °C, the
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to study the
th concrete
icated that
ng to 200 °C
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appear at 30
showed high
ck which res
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mples of nea
/min in orde
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th a heating
porosity is in
e capillary p
ting up to 2
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and water c
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e influence o
(NSC) and h
FA and GGB
C. However,
vere increase
ncrease and
00 °C and co
her resistan
sulted in spl
plementary m
perature u
t cement pa
er to prevent
and pore st
ggregate and
g rate of 1 °C
ncreased an
pores are inc
50 °C. Howe
emperature
re [Bažant,
narrow nec
can pass thro
argely widen
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of different
high strength
BS concrete s
SF concrete
e in permea
d lowest ave
ontinued to
ce to surfac
itting at 800
materials.
p to 300 °
aste made w
t thermal gr
27
tructure of
d hematite
C/min. The
d the pore
creased. A
ever, rapid
to 450 °C.
1979]. At
cks on the
ough them
ned due to
pozzolanic
h concrete
showed an
e exhibited
ability with
erage pore
grow until
ce cracking
0 °C as can
°C on the
with CEM I
adient and
Literature review 28
shocks. The results showed that the total porosity increased by about 12 % with heating up to 300
°C. Mechanical properties (elasticity and Poisson`s ratio) were reduced by about 17 %, which are in
agreement with the porosity results. Similar study was carried out by Piasta et al. [Piasta, 1984] on
the effect of elevated temperature on the microstructure of cement paste. He concluded that above
100 °C, water is evaporated and the generated steam affects the surrounding cement paste phases.
The temperature range of 100 ‐ 300 °C is suitable for formation of so‐called internal autoclaving. So,
additional hydration of unhydrated cement grains takes place. Up to 300 °C, the increase in total
porosity is relatively small due to additional hydration of unhydrated cement particles and increase
in the degree of carbonation. Similarly, Xu et al. [Xu, 2001] carried out a research to study the effect
of high temperature on porosity, durability and compressive strength of normal strength and high
strength concretes made of fly ash with replacement levels of 0, 25 and 55 %. The results indicated
that about 8 and 15 % increase in compressive strength has been gained for OPC and fly ash
concrete respectively after exposure to 250 °C. In addition, it was found that all concretes suffer
severe deterioration in permeability. He reported also that after exposed to 250 °C, the total
porosity is increased by about 1 ‐ 2 % only, and the pore diameter was coarsened. The micro‐
cracking was considered the main reason for deterioration when concrete exposed to high
temperature. Micro‐cracks is initiated around CH crystals and then around unhydrated cement
particles. Incorporation of fly ash reduces the thermal micro‐cracks due to the consumption of CH
and generation of additional C‐S‐H phases.
Li et al [Li, 1999] studied the microstructural characteristics of high performance concrete under
elevated temperature up to 200 °C intended for use in vault sealing in nuclear waste repositories.
Two types of concrete were used: one with oil well cement and the other with type K expansive
cement according to ASTM Standard C 192‐90a. It was found that concrete microstructure, matrix
morphology, mineral, and chemical composition showed no significant changes in the tested
temperature range up to 200 °C. Similar investigation was carried out by Khan et al. [Khan, 2010] to
study the effect of thermal cyclic loading with 200 °C on the properties of normal and fly ash
concrete. The results indicated that the compressive strength of plain and fly ash concrete is
increased with rising the heating cycles. The increase in compressive strength of fly ash concrete is
higher than that of normal concrete. It increased with increasing fly ash content up to 50 %.
However, with further increase of fly ash (i.e. 60 %), the increase in compressive strength with
heating is reduced and become lower than that with 20 % fly ash. Balendran et al. [Balendran, 2002]
presented an overview and discussion on the effect of high temperature on the strength and
durability of HPC incorporated pozzolanic materials. It is concluded that the addition SF reduces the
performance of HPC at high temperature. The risk of spalling and high loose of compressive strength
Literature review 29
are associated with addition of SF. On the contrary, the addition of FA and MK has been found to
enhance the performance of HPC for both residual strength and durability.
2.4.3 Explosive thermal spalling
When exposed to high temperature, concrete suffers several degradation processes. Spalling is one
of the most important phenomena that may take place during the high temperature exposure. It
refers to sudden and violent separation of a surface layer of heated concrete. It is accompanied by a
loud bang and quick liberation of a large amount of energy and detaching of fragments of the
exposed concrete surfaces and can make severe deteriorations for the structure [Phan, 2002]. It
takes place if the heating rate is high, typically 20 °C/min [Lee, 2008]. It is prone to happen in HSC
and HPC even at a lower heating rate because of the dense microstructure. The explosive spalling is
a brittle failure observed first by Harmathy in normal concrete subjected to fire [Bažant, 1996]. Two
main mechanisms are commonly known to explain the spalling risk [Mindeguia, 2010]. The first is a
thermo‐mechanical interaction. Heating of concrete elements causes high temperature gradients in
the first area of the hot surface. If the heating rate is rapid, high compressive stresses are generated
closed to the heated surface. As self‐equilibrium, thin layer near the heated surface will be in
compression while the interior part is in tension. The compressive stress in the thin layer in the
vicinity of the surface causes buckling and deportation of some pieces of concrete surface. The
second mechanism is a thermo‐hygral process. With heating to high temperature water inside the
concrete begins to vaporize, and as a result the pore pressure is sharply increased in the hot zones
which create a pressure gradient with cold zones. Because of the pressure differences, the vapour
tries to migrate to low pressure zones (cold zones) and condensed there because of the low
temperature. With continuous heating, more water is condensed in the cold zone until reaching the
saturation state. At this point, the vapour is forced to migrate through the hot dry zone to escape
into the atmosphere. If the permeability of concrete is slightly low and the rate of heating is rather
high, the vaporized water cannot escape fast, because the rate of vaporization is higher than the
rate of release to atmosphere. Spalling will take place when the summation of pore pressure and
thermal stresses is higher than the tensile strength of concrete. So, the probability of spalling
occurrence depends mainly on heating rate, saturation level and the permeability of concrete
[Consolazio, 1998]. If the concrete is cracked, the vapour pressure will release, and the probability of
explosive spalling is decreased [Lee, 2008].
Bažant studied the explosive spalling and found that the pore pressure can work only to trigger the
cracking but cannot make the explosion [Bažant, 1979]. He mentioned that another supply of
energy should make this explosion; it is the potential energy of the thermal stresses. Nevertheless,
the role of pore pressure cannot be neglected because the experiments confirmed that the
Literature review 30
explosive spalling occurred only in wet concrete which is saturated with water. Phan et al. [Phan,
2002; Phan, 2002] studied the explosive spalling in high strength concrete. Contrary to Bazant
explanation, it was found that internal pore pressure plays the primary cause, whereas the thermal
stresses play a secondary role in this failure. The w/c ratio has an important role in explosive
spalling; as it reduces, the risk of spalling increases. The addition of polypropylene fibers reduces the
pore pressure significantly and thereby reduced the tendency for spelling. It increases the
permeability during heating above 160 °C. It melts at a temperature of about 160 °C and provides
open channels in concrete to release the vapour and moisture [Khoury, 2000]. It is mentioned that
addition of 1.5 kg/m3 prevents the explosive spalling [Phan, 2002]. Noumowe and Debicki concluded
that addition of 2 % of polypropylene fibers by weight enhances the permeability of HPC and
reduces the risk of explosive spalling [Noumowe, 2002]. In the literature, many investigations have
been carried out in order to study the risk of explosive spalling of different types of concrete. The
following references provide further information about the explosive spalling of concrete when exposed
to high temperature [Bažant, 1979; Bažant, 1996; Chan, 1996; Consolazio, 1998; Kodur, 1999; Phan,
2001; Poon, 2001; Noumowe, 2002; Phan, 2002; Dehn, 2004; Hainz, 2004; Naus, 2006; Lee, 2008;
Mindeguia, 2010].
2.4.4 Effect of autoclaving on concrete properties
In some applications, concrete is subjected to both high temperature and saturated vapour
pressure. Nuclear power plant containment is an example where both hydraulic and thermal loads
attack concrete. In such applications, leak‐tightness of concrete should be ensured either by
installing a liner or by using very dense concrete in order to prevent water and vapour leakage. In
the French 1300 and 1400 MWe nuclear power plants, the reactor containment consists of two
concentric containments [Granger, 2001]. The outer one is designed to resist the external
environmental conditions; however the inner one is used to withstand the designed accidents (140
°C and 5 bars). In most containments the leak‐tightness is rely on a steel liner, but in the French
project, the leakage is controlled by using prestressed concrete wall with thickness of 120 cm. The
wall is designed to remain in compression during the accident. In the inner containment, HPC with
improved microstructure has been used in order to avoid the risk of thermal cracking, shrinkage and
to guarantee high impermeability. For similar application, Debicki et al. studied the leak‐tightness
integrity of containment wall made of HPC without liner under accidental conditions [Shekarchi,
2002; Shekarchi, 2003]. The test was carried out on HPC cylindrical specimens with 1.3 m thickness.
Two accidental conditions were applied; the first was 160 °C and 6.5 bars, and the second was 200
°C and 15 bars. The results indicated that after hydrothermal exposure, the permeability decreased
and no outgoing gas was measured through the specimen. Moreover, the maximum pressure was
found to be located near the heated surface and remains lower than the applied pressure and much
Literature review 31
lower than the tensile strength of concrete. The porosity measurements showed that the volume of
fine pores increases and the volume of big pores are decreased with slight increase of the total
porosity of about 2.2 % due to hydrothermal exposure with 200 °C and 15 bars.
In the last few years, several energy storage tanks have been built to store solar energy from
summer to winter time with storing temperature up to 95 °C. Most of these tanks are constructed
with normal concrete and the leak‐tightness is ensured by installing a steel liner. The economic
studies assessed the costs of the liner as about one‐fifth to one‐fourth of the total cost of the
project. In Stuttgart University a dense high performance concrete (HPC) has been developed in
order to be used in seasonal energy storage tanks without internal lining. The developed HPC has
been used in Hannover hot water tank with capacity of 2750 m3 to store water up to 95 °C without
internal steel liner. Jooß et al studied the permeability and diffusivity of the high dense HPC at high
temperature (up to 80 °C). The results showed that the permeability increased by about 62 % with
increasing the temperature from 20 to 50 °C, and by about 55 % with increasing the temperature
from 50 to 80 °C. Diffusivity also was increased by about 10 ‐ 21 % with increasing the temperature
from 20 to 50 °C and by 8 – 21 % by increasing the temperature from 50 to 80 °C [Jooß, 2002].
The behaviour of concrete under hydrothermal conditions is complex because concrete is subjected
to repeated cycles of heating and cooling as well as repeated cycles of vaporization and
condensation (autoclaving cycles). These conditions are similar to well cementing and autoclave
curing of aerated concrete to a large extent. The chemistry of autoclaving is different from that at
normal conditions or at heat only. In the first period of hydrothermal exposure, the strength is
increased due to the additional hydration of cement and pozzolanic materials. The high temperature
and high moisture content of concrete are ideal for creation of additional hydration products and
these in turn lead to microstructure densification as well as porosity and permeability reduction
[England, 1995]. Later, considerable reduction or increase of compressive strength is occurred due
to formation of different C‐S‐H phases depending on the temperature and the chemical composition
of the bulk materials [Mindess, 2003].
Ghosh and Nasser [Ghosh, 1996] carried out a research project in order to study the effect of high
pressure and temperature up to 232 °C on strength and elasticity of fly ash and silica fume concrete.
The results indicated that compressive strength and modulus of elasticity were decreased with
hydrothermal treatment at temperature of 232 °C. On the other hand, Hilsdorf [Hilsdorf, 1986]
studied the hydrated cement system under hydrothermal conditions and noticed a decrease in
strength and increase of porosity in the system of neat OPC. He reported that the loss of strength
can be prevented by addition of fly ash or ground quartz which is contrary to the finding of Ghosh.
Another study has been carried out by Xi et al. [Xi, 1997] on the effect of autoclaving with
Literature review 32
temperature of 125 and 175 °C on the properties of OPC and slag cement. The results revealed that
slag cement mix suffered strength loss after it reached the maximum strength. It lost more than 50
% of its original strength. In addition, the porosity was increased and the pore sizes became coarser.
However, the addition of silica fume enhanced the strength and reduced the porosity with
autoclaving. Moreover, the total porosity is reduced, the microstructure became denser and the
average pore radius became finer. These results have been interpreted as follow, the main
hydration product of the system of OPC‐slag is αC2SH and C‐S‐H (I). However, in the system
containing silica fume, the calcium ions is consumed and the pH of the pore solution is reduced. In
addition, the hydration reaction is totally changed and αC2SH is not more found. It was found also
that despite the hydrothermal treatment, the hydration of slag in the system OPC‐slag‐silica fume is
very slow due to the reduced pH value of the system.
2.4.5 Stability of C-S-H phases at hydrothermal conditions
Even though cement and concrete have been studied for several decades, questions still remain
about nature, morphology and interrelationship of hydration products and mechanisms of cement
hydration. Concrete is a heterogeneous material composed mainly of fine and coarse aggregate
bounded together by hydrated cement paste. Cement is the active constituents of concrete, and its
properties largely determine the performance of concrete. The primary constituents of OPC are C2S
and C3S, which make up about 70 ‐ 80 % of OPC [Ramachandran, 2001; Hewlett, 2003; Mindess,
2003; Aïtcin, 2004]. With addition of water at normal temperature, C2S and C3S start to hydrate
according to equation 2.6 and 2.7 [Nelson, 1990; Bažant, 1996; Barnes, 2002; Neville, 2004].
2C3S + 6H C3S2H3 + 3Ca(OH)2 (2.6)
2C2S + 4H C3S2H3 + Ca(OH)2 (2.7)
Under ambient conditions of temperature and pressure, the main product of OPC hydration (more
than 50 %) are the very low crystalline calcium silicate hydrates (C‐S‐H). It is an amorphous phase of
variable composition, and therefore, is usually written as C‐S‐H, which mean that no particular
chemical composition is implied [Taylor, 1997; Barnes, 2002; Mehta, 2006]. The exact structure of C‐
S‐H is not easily determined because it is too irregular and disordered [Neville, 2004]. However, it
can be roughly considered as a layered structure with large surface area, ranging from 100 to 700
m2/g [Mehta, 2006]. The formed C‐S‐H is a strong binding material responsible for strength of
cement based materials at temperature up to 110 °C due to Van der Waals force of attraction and
chemical bond [Noumowe, 2002; Mindess, 2003]. It has very low solubility in water under ambient
conditions, and its specific density varies between 2.3 ‐ 2.6 depending upon its chemical
composition, age, water/solid ratio, and temperature [Mindess, 2003]. The lime/silica ratio (C/S) is
Literature review 33
one of the most important characteristics of C‐S‐H gel that governs its stability and performance, in
particular, at high temperature. For OPC, it ranges from 1.5 ‐ 2 depending on the measurement
method [Taylor, 1986; Bažant, 1996; Ramachandran, 2001; Mindess, 2003; Neville, 2004; Mehta,
2006; Lee, 2008]. In addition to the C‐S‐H gel, about 20 ‐ 25 % of the hydration products of OPC is
high crystalline hexagonal plates of calcium hydroxide (CH) with specific density of about 2.24
[Taylor, 1997; Ramachandran, 2001; Hewlett, 2003; Mindess, 2003; Mehta, 2006]. The use of
supplementary materials consumes the CH and reduces the C/S ratio of the formed C‐S‐H depending
upon the replacement level [Meller, 2005].
When exposed to hydrothermal conditions, the microstructure of concrete is subjected to strong
alteration. C‐S‐H gel which is an excellent binding material at ambient conditions becomes unstable
and can be transformed to different phases with lower compressive strength and higher
permeability at high temperature [Jupe, 2008; Meducin, 2008]. C‐S‐H systems are very complex with
more than 30 stable phases [Taylor, 1997; Shaw, 2000; Garbev, 2004]. When C‐S‐H gel of OPC is
subjected to autoclaving with temperature higher than 110 °C in the absence of reactive silica, it is
quickly converted to lime‐rich phases with high crystallinity [Hewlett, 2003; Mindess, 2003]. Phases
such as αC2SH, hillebrandite and ‐tricalcium silicate are the most stable phases in the system with
high lime content. These phases are accompanied by an increase in the density which causes
shrinkage of the solid products and therefore the porosity increases and the strength is markedly
decreased [Taylor, 1997; Glasser, 2003; Mindess, 2003; Luke, 2004]. The loss of strength due to
hydrothermal treatment is commonly known as strength retrogression [Nelson, 1990; Taylor, 1997;
Barnes, 2002; Hewlett, 2003; Meller, 2009]. The lime‐rich phases are detrimental for the mechanical
properties and durability of concrete. The addition of siliceous materials such as fine quartz can
significantly modify the system and change the structure and morphology of the formed phases.
Small amount of silica brings the C/S ratio of the bulk to about 2, which is the ideal for formation of
αC2SH [Taylor, 1997]. However, with large addition of silica, pozzolanic reaction is accelerated,
portlandite is consumed, C/S is considerably reduced and the formation of lime‐rich C‐S‐H phases is
prevented [Nelson, 1990; Glasser, 2003]. Instead, numerous silica‐rich phases such as gyrolite,
xonotlite and 1.1 nm tobermorite are formed. The optimum addition of quartz is the maximum
which can be taken up in the reaction [Taylor, 1997]. It ranges between 35 ‐ 40 % of the binder
depending upon the chemical composition of the bulk materials [Nelson, 1990; Barnes, 2002;
Hewlett, 2003; Mindess, 2003; Ramachandran, 2003; Meller, 2005]. These silica‐rich phases are
generally associated with high compressive strength and lower permeability. With addition of
sufficient amount of silica, 1.1 nm tobermorite is the dominant below 180 °C. However, with higher
temperature it converts to xonotlite with minimal deterioration [Taylor, 1997; Barnes, 2002]. It is
demonstrated that the highest strength is associated with formation of tobermorite and the lowest
Literature review 34
with αC2SH formation [Ramachandran, 2001]. Xonotlite gives compressive strength lower than that
of tobermorite by about 20 – 25 %. Truscottite gives even lower strength than xonotlite but its
permeability is lower than xonotlite [Luke, 2004]. With very low C/S ratio, only gyrolite is formed at
200 °C [Meller, 2005; Meller, 2009]. The phase transformation under hydrothermal conditions can
be written as in the following equations:
C-S-H gel + CH C-S-H Phases (high C/S) ( 2.8)
C-S-H gel + CH + Silica C-S-H phases (low C/S) (2.9)
Tobermorite can be considered as one of the most important phases of cement hydration products
at normal and high temperatures. It can be classified into three types: 1.4 nm, 1.1 nm, and 0.9 nm.
1.4 nm tobermorite is formed below 80 °C, whereas 1.1 nm tobermorite is built in water at
temperature greater than 100 °C [Fujii, 1983; Shaw, 2000; Garbev, 2004]. It decomposes to 0.9 nm
tobermorite with heating at 300 °C [Shaw, 2000]. Several approaches have been carried out to
clarify the process and mechanism of tobermorite formation [Tsuji, 1991; Luke, 2004; Meller, 2005;
Meller, 2009; Kikuma, 2011; Matsui, 2011]. It is strongly affected by maximum temperature,
reactivity and amount of added silica, the addition of aluminium compounds and the addition of
alkali [Matsui, 2011]. The high reactive amorphous silica supports the formation of tobermorite by
enhancing the polymerization of C‐S‐H [Matsui, 2011]. The optimum addition of silica promotes the
formation of C‐S‐H with C/S ratio of 0.9 ‐ 1, which tends to crystalize to 1.1 nm tobermorite. At
higher temperature, tobermorite can be converted to xonotlite with volume reduction [Taylor,
1997; Jupe, 2008]. This volume reduction can be prevented by the addition of some aluminium,
which extends the stability of 1.1 tobermorite at higher temperature. The addition of aluminium
reduces the quartz solubility and thereby accelerates the formation of tobermorite and retards the
xonotlite formation [Taylor, 1997]. It is thought that aluminium ions may enter the lattice of the
tobermorite in expense of silicon ions and affect its properties and crystallinity [Kalousek, 1957;
Beaudoin, 1979; Jupe, 2008]. On the other hand, quartz reactivity has a significant role in
tobermorite formation. When reactive quartz is used as a source of silica, in the early stage
tobermorite is crystallized rapidly, but at late stage the rate of crystallization of tobermorite is
significantly reduced. However, when less reactive quartz was added, the formation of tobermorite
is continuing until reaching the equilibrium state. The final content of tobermorite is much more
than that in the case of reactive silica. However, in all cases at least about 10 % of the added quartz
does not react at all [Siauciunas, 2004].
The reaction of silica with lime is a pozzolanic reaction which is accelerated with autoclaving. So,
pozzolanic materials such as fly ash and silica fume could be used as sources of silica. By the use of
Literature review 35
pozzolanic materials, portlandite is consumed during the pozzolanic reaction, and its absence is
advantageous for concrete from the viewpoint of aggressive attack of chemicals [Jupe, 2008]. In
addition, high pozzolanic materials help to prevent the formation of lime‐rich phases such as alpha
dicalcium silicate because of the high content of silica. Luke studied the influence of hydrothermal
conditions at 180 °C on various systems containing OPC, class C and F fly ash, silica fume and quartz
flour [Luke, 2004]. The results showed that with addition of 35 % of class C fly ash, αC2SH with C/S
ratio of about 1.92 is the predominant phase, and therefore, very low compressive strength is
obtained. However, replacing OPC with 35 % class F fly ash reduced the C/S ratio to 1.38 and at this
ratio αC2SH formation competes with the formation of silica‐rich phases such as poorly crystalline
tobermorite and hydrogrossular‐type phases. As a result, the compressive strength is relatively low;
however it is higher than that of 35% class C fly ash. In the case of silica fume addition (35 % of
cement), very low compressive strength of the products is observed. In this system, despite of the
high silica content in the system, the predominant phase is αC2SH. In addition, a number of different
metastable phases are formed, most of which are undefined. On the other hand, by addition of 35 %
quartz flour to cement, xonotlite was the major phases in the system and the compressive strength
was higher than fly ash and silica fume cases. With a combination of 30 % class F fly ash and 35 %
quartz flour, the bulk C/S ratio of the system was 0.64. At this ratio, the predominant phase is the
highly crystalline 1.1 nm tobermorite which is accompanied with high compressive strength.
However, combination of 35 % quartz and 30 % silica fume resulted in quite increase in compressive
strength which equals about 50 % of the cement‐class F fly ash‐quartz system.
Meller et al. carried out several researches to study the system of cement, silica, alumina and water
at different temperatures up to 350 °C [Nelson, 1990; Meller, 2005; Meller, 2007]. They developed a
diagram for the Cao‐Al2O‐SiO2‐H2O system (CASH) based on Taylor work (Figure 2.13). The results of
their work revealed that under hydrothermal condition at 200 °C, pastes made of neat Portland
cement exhibited portlandite and lime‐rich phases such as αC2SH and jaffeite which are deleterious
to compressive strength. With small addition of silica and alumina (< 25 %), the C/S ratio was still
high thereby hillebrandite and α C2SH are formed. However, at higher temperature these phases are
not found because they are replaced by reinhardbraunsite. With increasing silica addition to 35 %,
the C/S ratio is reduced to about 1 which promoted the formation of silica‐rich phases in expense of
lime‐rich ones. 1.1 nm tobermorite is formed at temperature higher than 110 °C, and transformed
to xonotlite or gyrolite at about 150 °C depending upon the quantity of the added silica. With
addition of 20 ‐ 50 % silica to the system at 200 °C, 1.1 tobermorite coexisted with xonotlite. The
addition of more quartz leads to formation of gyrolite and the excess quartz is remained with it.
Tobermorite decomposes normally at 150 °C to form xonotlite and gyrolite, however the addition of
aluminium stabilized the tobermorite at higher temperature up to 250 °C. When silica addition
Literatur
exceede
gyrolite
aluminiu
Figure 2[Meller, 20
Kyritsis
microstr
2009]. C
permeab
adding a
are form
improve
improvem
Regardin
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When b
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system, t
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decrease
re review
d 40 %, gyr
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2.13: The fo007]
et al. stu
ructure of ce
Cement, silic
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36
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37
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Literature review 38
Materials and methods 39
3. Materials and methods
3.1 Introduction
To achieve the objectives of this investigation, the research has been divided into three parts:
1. Optimizing a dense high performance concrete mixture.
2. Study the effect of hydrothermal conditions on the properties of densely packed concrete.
3. Studying the influence of autoclaving on the properties of cement paste.
For the first two parts, twenty three concrete mixes have been prepared, cured, and tested. All
these mixes have approximately similar aggregate grading and content, whereas the differences are
only in the cementitious materials composition and water/binder ratios. The experimental work
includes the measurements of properties of fresh concrete. In addition, durability and mechanical
properties were measured at ambient conditions and after hydrothermal exposure (200 °C and 15.5
bars) for several autoclaving cycles, up to 50. To study the effect of hydrothermal treatment on C‐S‐
H stability and properties, 10 cement pastes have been prepared and tested. Details of the
compositions and tests of these pastes are presented in chapter 7.
3.2 Materials
3.2.1 Aggregates
Natural quartzite aggregates with maximum aggregate size of 16 mm has been used in this
investigation. The coarse and fine aggregate were dried until constant weight and then stored in the
room temperature before use. A mean specific density and water absorption of 2.61 and 0.5 % were
obtained for the used aggregates respectively. Three aggregate classes were used in the experiments:
0 ‐ 2, 2 ‐ 8, and 8 ‐ 16 mm. The sieve analysis of the used aggregate is presented in Figure 3.1.
Figure 3.1: Sieve analysis of the used aggregate
0
10
20
30
40
50
60
70
80
90
100
0.125 0.25 0.5 1 2 4 8 16 32
Cumulative passing %
Sieve size mm
Aggregate 8‐16
Aggregate 2‐8
Sand 0‐2
Material
3.2.2 C
In this in
Portland
N). In ad
N‐LH/NA
68 %). C
and Tab
laborato
using las
of ceme
Figure 3
Table 3.
CEM I 32
CEM I 42
CEM III/A
CEM III/B
Table 3.
CEM I 32
CEM I 42
CEM III/A
CEM III/B
* Without
ls and metho
Cement
nvestigation,
d cement wi
ddition, blast
A with slag c
Chemical com
ble 3.2 res
ory. Figure 3
ser granulom
nts was mea
3.2: Laser gra
.1 Chemica
Ca
2.5 63
2.5 65
A 54
B 46
.2 Physical
Blaine(cm
2.5 3
2.5 3
A 3
B 4
t superplasticize
ods
, several typ
th two diffe
t furnace sla
content of ab
mposition a
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3.3 shows th
metry (MALV
asured using
anulometry t
l compositio
O SiO2
.2 20.80
19.9
.8 23.7
29.7
properties
e Fineness m2/g)
3450
3500
3860
4156
er according to
pes of ceme
erent streng
ag cement w
bout 50 % a
nd physical
The physica
he measured
VERN) as des
g Helium pyc
to measure
on of differe
Al2O3 F
4.61 2
4.6 3
8.8 1
10.12 1
of the used
Water
Puntke [Puntke
nts accordin
th classes h
with two diff
nd CEM III/B
properties
al propertie
d particle si
scribed in [H
cnometry.
the particle
nt cements
Fe2O3 Mg
2.59 1.7
3.1 1.7
1.46 5.2
1.62 8
cement
r demand (%
25.6
24.8
25.1
26.4
e, 2002]
ng to DIN EN
ave been us
ferent slag c
B 32.5 N‐LH/
of the used
es were de
ze distribut
Hackley, 2004
size distribu
(according
gO Na2O
7 0.16
7 0.31
21 0.3
0.31
%)* D(g
N 197‐1 have
sed (CEM I 3
content were
/HS/NA with
d cements a
termined e
ion of differ
4]. In additio
ution of fine m
to the prod
K2O SO
0.50 2.7
0.5 3.0
0.59 2.4
0.65 2.4
ensityg/cm3)
Se
3.17
3.12
3.01
2.96
e been used
32.5 R and C
e used (CEM
h slag conten
re shown in
experimenta
rent types o
on, the spec
materials
ucers)
O3
70
0
4
49
etting time (
Initial
105
140
235
285
40
d. Ordinary
CEM I 42.5
M III/A 32.5
nt of about
n Table 3.1
ally in the
of cements
ific density
(min)
Final
180
210
285
340
Materials and methods 41
Figure 3.3: Particle size distribution of the used cements measured with laser granulometry
3.2.3 Fly ash
Fly ash is a waste product, remaining from the combustion of hard coal for energy production
purposes. Around 18 million tons of hard coal fly ash is produced in Europe yearly. Most of it is
consumed by the building materials sector, where it is used as a major ingredient for the cement
production or as additive material for the concrete production [Hunger, 2010]. In this research, Class
F fly ash according to DIN EN 450‐1 has been used. Three different sizes of fly ash have been used in
this investigation; normal fly ash, fine fly ash (M20) and fine fly ash (M10) with mean particle sizes of
17, 9, and 5 µm respectively. Table 3.3 shows the chemical composition of fly ash used in this
investigation according to the producers. However, physical properties of fly ash have been
determined experimentally. Table 3.4 shows the measured characteristics of different types of fly
ash. Figure 3.4 shows the particle size distribution of the used fly ash measured by laser granulometry.
In addition, SEM measurement of fine materials has been performed as can be seen in Figure 3.5.
Figure 3.4: Particle size distribution of the used fly ash
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
Cumulative passing %%
Size (µm)
CEM I 32.5 RCEM I 42.5 NCEM III A 32.5CEM III B 32.5
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
Comulative passing %
Size (um)
M10M20FA
Material
Table 3.
M10
M20
Fly ash
Table 3.
M10
M20 Fly ash * Without
Figure 3
ash (M2
3.2.4 S
Silica fu
element
extreme
grade 9
properti
the part
ls and metho
.3: Chemica
CaO
6
5
3.1
.4: Physical
Blai
superplasticize
3.5: Scannin
20), c) fine fl
Silica fume
me is very
tal silicon o
ely small par
71 accordin
es of the us
icle size dist
ods
al compositi
O SiO2
53
52
49.2
properties
ne Fineness
6400
6000 2877
r according to P
ng electron
ly ash (M10
e
fine non‐cr
r alloys con
rticle size, a
ng to DIN
ed silica fum
ribution of t
on of the us
Al2O3 Fe
25
25
27.6 7
of the used
s (cm2/g)
Puntke [Puntke,
microscopy
0), d) silica f
rystalline m
ntaining silic
nd large sur
EN 13263‐1
me are given
the used silic
sed fly ash (
e2O3 MgO
6 1
6 1
7.6 2.1
fly ash
Water dem
22
220
, 2002].
y (SEM) of f
fume
aterial prod
con. It is a
rface area. I
1 has been
n in Table 3.5
ca fume.
a
c
(according t
O Na2O K2
1.5 1
1.5 1
0.90 5
mand (%)*
2.1
220.8
fine materia
duced as a
morphous m
In this expe
n used. Che
5 and Table
to the produ
2O SO3
1.9 1.1
1.9 1.1
5.0 0.7
Specific d
als particles
by‐product
material wit
rimental wo
emical comp
3.6 respecti
ucer)
density (g/cm
2.49
2.45 2.29
: a) fly ash,
of the pro
th high SiO
ork, Elkem m
position an
ively. Figure
b
d
42
m3)
b) fine fly
duction of
O2 content,
micro silica
d physical
3.6 shows
Materials and methods 43
Table 3.5: Chemical properties of silica fume (according to the producer)
CaO SiO2 Al2O3 Fe2O3 MgO Na2O K2O SO3 Cl
0.2 98.4 0.2 0.01 0.10 0.15 0.20 0.10 0.01
Table 3.6: Physical properties of silica fume
Fineness cm2/g* Water demand (%)** Density (g/cm3) Bulk weight (kg/m3)*
200000 51.8 2.2 500
* Densified according to Manufactures datasheet, ** Measured without superplasticizer according to Puntke [Puntke, 2002]
Figure 3.6: Particle size distribution of silica fume
3.2.5 Filler
In this research, the term filler mean the powder materials which applied in concrete to achieve high
packing density, it is almost non‐reactive at ambient temperature. In this investigation, two different
types of commercially available quartz filler which meet the requirements of DIN EN 12620 were
used: quartz powder and quartz sand. The mean particle size of quartz sand (QS) and quartz powder
(QP) are about 180 and 60 um respectively. Chemical composition of the used fillers can be found in
Table 3.7. However, physical properties and particle size distribution have been experimentally
determined as can be seen in Table 3.8 and Figure 3.7 respectively.
Table 3.7: Chemical composition of quartz sand and quartz powder (according to the producer)
CaO SiO2 Al2O3 Fe2O3 MgO Na2O K2O
Quartz sand 98.5 0.7 0.06
Quartz powder 0.013 99.61 0.11 0.012 0.004 0.006 0.024
0
10
20
30
40
50
60
70
80
90
100
0.01 0.1 1 10 100
Cumulative passing %
Particle Size (um)
Materials and methods 44
Table 3.8: Physical properties of quartz sand and quartz powder
Blaine Fineness (cm2/g) Water demand (%)* Density g/cm3
Quartz sand 760 ‐ 2.67
Quartz powder 2683 24.4 2.69
*Without superplasticizer according to Puntke [Puntke, 2002]
Figure 3.7: Particle size distribution of quartz sand (QS) and quartz powder (QP) measured with
laser granulometry
3.2.6 Superplasticizer
In this investigation, to achieve the satisfied consistency class, superplasticizer (Muraplast FK 63.3) has
been used. The used superplasticizer is polycarboxylate‐based (PCE), as that type proved to be very
effective in densely packed systems with fine particles [Hunger, 2010], and it complies with DIN EN
934‐2. It has a density of about 1.06 g/cm3, and the recommended dosage is 2 ‐ 50 g per kg of cement.
3.3 Specimens preparation and curing
The concrete was mixed in a mixer with capacity of about 60 liters. In order to enhance the
distribution of all particles and make the mixture more homogenous, the sequence of the addition
of concrete constituents into the mixer has been carried out according to the following diagram
(Figure 3.8). The mixing procedures for all mixes were performed in the same manner. After mixing,
fresh concrete properties were measured. Then, the moulds were cast and compacted to remove
any entrapped air and to ensure full compaction according to DIN EN 12390‐2. A number of test
specimens, mainly 100 mm cubes and 150 x 300 mm cylinders were prepared from each mix for
different tests according to DIN EN 12390‐1. After 24 hours of adding the water to the mixture, the
test specimens were demoulded. The curing process took place in water basin at temperature of 20
± 1 °C until the day of testing.
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
Cumulative passing %
Particle Size (um)
QP
QS
Material
Addit
p
Additio
Additio
Figure 3
3.4 Te
3.4.1 F
3.4.1.1
In this in
It is basi
manner
of the di
Figure 3
ls and metho
tion of aggre
powder and
1/2 minu
on of part of
mixing for
on of silica fu
3.8: The seq
ests
Fresh conc
Consisten
nvestigation,
cally a meas
for 15 times
iameter from
3.9: Determin
ods
egates and q
quartz sand
te mixing
f mixing wat
1/2 minute
ume, M10 an
quence of ad
crete prope
ncy
, consistency
surement of
s in around
m 3 different
ning the con
quartz
d
ter and
nd M20
ddition of co
erties.
y was measu
f the spread
30 seconds.
t directions
crete consis
oncrete con
ured using a
of a fixed q
The mean d
as can be se
stency using
Ad
Add
stituents in
a flow table t
quantity of c
diameter is c
een in Figure
g flow table te
1/2 min
ddition of ce
1/2 min
dition of res
and sup
Mixing f
the mixer a
test accordi
oncrete afte
calculated fr
e 3.9.
est accordin
nute mixing
ement and f
nute mixing
sidual mixin
perplasticizer
for 2 minute
and the mixi
ng to DIN EN
er jolting in
rom the mea
ng to DIN EN
45
fly ash
g water
r
es
ng time
N 12350‐5.
a standard
asurement
N 12350-5
Materials and methods 46
3.4.1.2 Air content
The air content of the fresh concrete mixes has been determined according to DIN EN 12350‐7. In
this test, a standard five liters steel cylinder is fully filled with fresh concrete and compacted. Then,
the cover is fixed and the pressure is applied on to the surface of concrete in the bowl, causing a
change in the volume. This change is attributed to the air in the concrete since other constituents in the
bowl are incompressible. The air content of concrete is then directly read from the scale on the cover.
3.4.1.3 Fresh density
The fresh concrete density has been measured as specified in DIN EN 12350‐6. A five liters bowel is
filled and compacted until no large bubbles of air appear on the surface. After compaction, the top
surface of concrete shall be struck off and finished smoothly. All excess concrete shall then be
removed and the filled bowel is weighed. The density of fresh concrete is the weight of net concrete
divided by the volume of the bowel.
3.4.2 Mechanical properties.
3.4.2.1 Compressive strength
The compressive strength of concrete was determined using 100 mm cubes at ages of 28 and 91
days according to DIN EN 12390‐3. A modern digital crushing machine (Toni Technik) was used. After
curing period, the specimens were dried at room temperature (20 ± 1 °C). Then, compressive strength
test was carried out. Three cubes of each mix were tested and the mean value was considered.
3.4.2.2 Splitting tensile strength
The splitting tensile strength test was applied on cylinders (150 mm x 300 mm) according to European
Standard DIN EN 12390‐6. The following formula was used to determine the splitting tensile strength.
s
t
ld
F
2
(3.1)
Where: Ft is the force in KN, L is the specimen length in mm and ds is the specimen diameter of in mm.
3.4.2.3 Modulus of elasticity
The modulus of elasticity of concrete has been determined on cylinders (150 mm x 300 mm)
according to European standard EN 1048‐5. Concrete samples were prepared and cured under
water until the testing day. At age of 91 days, the specimens were dried at room temperature (20 ±
1 °C). After that, the static modulus of elasticity was determined (Toni Technik) as can be seen in
Figure 3.10.
Material
Figure 3
3.4.2.4
The den
volume o
Where M
3.4.2.5
The rebo
concrete
compres
surface w
were fix
samples
influence
ls and metho
3.10: Determ
Density of
sity of harde
of about 1 li
Mc is the ma
Rebound
ound hamm
e. By refere
ssive strengt
which shoul
ed in the m
before and
e of hydroth
ods
mination of m
f hardened
ened concre
ter. The foll
cc V
M
ss of concre
Hammer
mer accordin
nce to the c
th. When co
ld be flat an
achine as ca
d after auto
hermal cond
modulus of
concrete
ete has been
owing formu
c
c
V
M
te sample (k
ng to DIN E
conversion c
onducting th
nd smooth. I
an be seen i
oclaving for
itions on co
elasticity of
n determined
ula has been
kg) and V is t
EN 12504‐2
chart, the re
he test, the h
t has been u
in Figure 3.1
5, 15, and
ncrete hard
f concrete a
d according
n implement
the volume
has been u
ebound valu
hammer sho
used perpen
11. The mea
50 cycles in
ness.
ccording to
to DIN EN 1
ted to calcul
(3
of concrete
used to mea
ue can be u
ould be held
ndicularly to
asurement w
n order to e
DIN 1048-5
2390‐7 on a
late the den
3.2)
specimen (m
asure the ha
used to dete
d at right ang
o the specim
was done for
exactly dete
47
5
a cube with
sity:
m3).
ardness of
ermine the
gles to the
mens which
r the same
ermine the
Material
Figure 3
hammer
3.4.3 D
3.4.3.1
Permeab
Numero
concrete
to DIN E
of 5 bars
of penet
the split
Figure 3
ls and metho
3.11: Determ
r) according
Durability o
Water per
bility is the
us test meth
e [Dinku, 199
EN 12390‐8 w
s to the surf
tration of th
surface of t
3.12: Determ
ods
mination of
g to DIN EN
of concrete
rmeability
ease with w
hods have b
96]. In this i
was used. T
face of harde
he waterfron
the tests spe
mination of w
hardness o
12504-2
e
which liquid
been develo
investigation
he basic pri
ened concre
nt is measur
ecimen (mois
water penet
of concrete u
ds or gases
ped and are
n, the water
nciple of thi
ete for 72 ho
red. The dep
st concrete
tration depth
using non-d
can travel t
e in use to e
r penetration
is test is tha
ours. The spe
pth of penet
being darke
h of concret
destructive t
through con
valuate the
n depth und
at water is a
ecimen is th
tration is fo
r as can be s
te according
test method
ncrete [Nevi
water perm
der pressure
pplied unde
en split and
und by obse
seen in Figur
g to DIN EN
48
d (rebound
ille, 2008].
meability of
e according
er pressure
d the depth
ervation of
re 3.13).
N 12390-8
Material
Figure 3
3.4.3.2
In this in
Because
dried in
tempera
and 20 m
specime
permeab
Where:
height o
dynamic
Figure 3
ls and metho
3.13: Determ
Air perme
nvestigation,
of the impo
n the oven
ature and sen
mm thicknes
n. The time
bility coeffici
K
Kair is air pe
f the concre
c viscosity of
3.14: Determ
ods
mination of t
ability
, the air perm
ortant effect
until cons
nt to air per
ss is fixed in
at which a u
ent can be o
tA
VK f
air .
rmeability c
ete sample (
f air in N.s/cm
mination of a
the water pe
meability of
t of moisture
stant weigh
meability de
n the device.
unit volume
obtained usin
pt
h
a .
..
coefficient (c
cm), A: cros
m2.
air permeab
enetration d
concrete ha
e content on
t. Then, th
evice. In this
. Air flow un
of the gas p
ng the Hagen
cm2), Vf: flow
s section are
bility of conc
depth (moist
as been mea
n air permea
he specimen
test, a conc
nder pressur
passes throu
n‐Poiseuille f
w volume (c
ea of the sa
crete accord
t concrete b
asured accor
ability, the sa
ns were co
crete specim
re is applied
gh the speci
formula [Din
cm3), ta: pass
mple (cm2),
ding to TGL
being darker
rding to TGL
amples have
ooled down
en of 50 mm
on one surf
imen is mea
nku, 1996]:
sing time (se
p: pressure
21094-12
49
r)
21094‐12.
e been first
n to room
m diameter
face of the
asured. The
(3.3)
econds), h:
N /cm2, η:
Material
3.4.3.3
A standa
water is
containe
pulls wa
determin
the incr
coefficie
Figure 3
15148
3.4.3.4
The test
chloride
or morta
applicati
determin
penetrat
diffusion
depth of
The follo
ls and metho
Absorption
ard method
included in
er of water s
ater up into
ned over va
rease in ma
ent of concre
3.15: Determ
Chloride d
t to determ
to be deter
ar specimen
ion, the spe
ned by mea
tion depth,
n coefficient
f chloride th
owing equat
ods
n
of evaluatin
n DIN EN ISO
such that th
o the specim
rious period
ass versus
ete can be ca
mination of
diffusion tes
mine the ch
rmined with
under the i
cimen is spl
ns of indicat
the applie
t was meas
rough the co
ion was use
ng the water
O 15148. Th
e immersion
men is the c
ds of time u
the square
alculated.
water abso
st
loride migra
in a short p
influence of
lit and the p
tor solutions
ed voltage,
sured accor
oncrete spe
d to determ
r uptake of a
e method in
n depth of t
capillary suc
p to 24 hou
root of tim
rption coeffi
ation coeffic
eriod of tim
f an electrica
penetration
s. The chlori
and other
ding to BAW
cimen was d
mine the diffu
a concrete sa
nvolves plac
the specime
ction. The in
rs. Then a s
me. From t
icient of con
cient enable
me. The pene
al field is exa
depth of the
ide diffusion
parameters
W Merkblat
determined
usion coeffic
ample which
cing a concre
n is 5 mm. T
ncrease of t
straight line
this relation
ncrete acco
es the resis
etration of c
amined. At t
e front of th
n coefficient
s. In this re
tt [BAW, 20
after 7 days
cient:
h partially im
ete specime
The primary
the specime
is fitted to t
nship, the a
ording to DIN
stance of co
chlorides into
the end of t
he free chlor
is calculate
esearch, th
012]. The p
s of beginnin
50
mmersed in
en within a
force that
en mass is
the plot of
absorption
N EN ISO
oncrete to
o concrete
the voltage
ride ions is
d from the
e chloride
enetration
ng the test.
Material
With
Where:
Dcl: Z: F: U: R: T: h: xd: t: erf ‐1: cd: co:
Figure 3[BAW, 20
3.4.4 C
3.4.4.1
The effe
water di
weight s
constant
ls and metho
2
migration cvalency, forFaraday conabsolute pogas constanabsolute mheight of thmean peneduration ofinverse errochloride cochloride co
3.16: Determ12]
Concrete m
Effective p
ective porosi
isplacement
should be m
t weight. Fr
ods
coefficient (mr chloride ionstant, F = 9otential diffent, R = 8.315ean temperhe test specitration deptf the test (s) or function ncentration ncentration
mination of c
microstructu
porosity
ity which is
t. The sampl
easured. Th
om the kno
12
m2/s) ns z = 1 9.649*104 J.erence (V)5 J* (K*mol)‐
ature of themen (m)th of the chl
at which thof the potas
chloride diff
ure
accessible b
es must be
hen, the satu
owledge of t
(Volt.mol)‐1
1
e solutions d
oride ions in
e colour chassium hydro
fusion coeffi
by water has
saturated u
urated samp
the weight i
uring the te
n each half o
anges, cd = 0oxide solutio
cient
s been meas
under water
ples are dried
in both dry
(3
(3
st (K)
of the test sp
0.07 (mol.l‐1)on (mol.l‐1)
sured using
at least for
d in oven at
(mdry) and s
3.4)
3.5)
pecimen (m)
)
the simple
24 hours an
t 105 °C with
saturated st
51
)
method of
nd the wet
h dry air to
tates (msat)
Material
and the
equation
3.4.4.2
The heliu
inside th
Concrete
concrete
pycnome
the open
Where ε
sample b
Figure 3
3.4.4.3
The prin
the pore
ls and metho
weight und
n:
o
Helium py
um pycnom
he pores is s
e specimen
e pieces we
etry (microm
n porosity ca
ε is the tota
by its volum
3.17: Helium
Mercury in
nciple of this
es of a dried
ods
der water (m
sat
sat
m
m
ycnometry
etry is a dev
substituted
is dried at
ere finely gr
metrics) to
an be calcula
(1
al porosity,
e), ρs is the s
m pycnometr
ntrusion po
s technique
d and evacu
msub), the ef
sub
dry
m
m
vice used to
by helium a
105 °C with
round (< 0.
measure dir
ated by the f
)s
b
ρb is the b
specific den
ry device us
rosimetry (
is based on
ated porous
ffective por
measure th
and the amo
h dry air to
063 mm). T
rectly the sp
following eq
ulk density
sity, (determ
sed to meas
(MIP)
n penetratin
s medium. T
osity (εo) ca
e specific de
ount of the i
constant w
Then the sa
pecific dens
quation:
(calculated
mined by usi
sure the spe
g a non‐rea
The dried sa
an be calcul
(3
ensity of por
inert gas is d
weight. Samp
amples wer
ity. By know
(3
by dividing
ng helium p
ecific densit
cting liquid
mple is plac
ated by the
3.6)
rous materia
detected [Kr
ples of abou
e sent to t
wing the bu
3.7)
g the dry m
pycnometer)
ty of concret
such as me
ced into a d
52
e following
als. The air
rus, 1997].
ut 5‐7 g of
the helium
ulk density,
mass of the
.
te
ercury, into
ilatometer
Material
and evac
(Porosim
used to
expresse
Where:
applied
measure
Figure 3concrete
3.4.4.4
It is a the
measure
phenom
provide
ls and metho
cuated. The
meter 2000 W
calculate th
ed as:
r(
r is the rad
pressure (b
ements proc
3.18: Mercue
Thermal g
ermal analys
ed as a func
mena, such a
informatio
ods
pressure is
WS ) where
he porosity.
mp
cos..2(
ius of the in
bar), and θ
cedures can
ry intrusion
gravimetric
sis method i
ction of inc
as phase tra
on about c
then raised
the pressur
The relation
)
ntruded por
is contact a
be found in
porosimetr
analysis (T
in which cha
creasing tem
ansitions inc
chemical ph
to atmosph
re is monito
nship betwe
re (nm), γ is
angle betwe
[Gluth, 2011
ry to measu
TGA)
anges in phy
mperature. T
cluding vapo
henomena
eric pressure
ored automa
een the pore
surface ten
een mercur
1].
ure the poro
ysical and ch
TGA can pro
orization an
including c
e before it is
atically. The
e size and th
(3.8)
nsion of me
ry and the
osity and po
emical prop
ovide inform
nd desorptio
chemisorpti
s fitted to th
Washburn e
he exerted p
rcury (N/m)
pore walls.
ore size dist
perties of ma
mation abou
on. Likewise
on dehydra
53
he machine
equation is
pressure is
), pm is the
Details of
tribution of
aterials are
ut physical
e, TGA can
ation and
Material
decomp
and the
measure
(TherMa
and afte
Figure 3
ls and metho
osition. As t
weight pe
ement proc
ax 700) is us
r autoclavin
3.19: Therm
ods
the tempera
ercentage of
edures can
sed to meas
ng for 50 cyc
ogravimetry
ature increa
f each resu
be found
ure the CH
les.
y to measur
ses, various
ulting mass
in [Ramac
content of d
re the weigh
component
change can
chandran, 2
different cem
ht loss of co
ts of the sam
n be measu
2001]. In th
ment pastes
oncrete sam
mple are de
ured. More
his investiga
s at normal
ple with hea
54
ecomposed
details of
ation, TGA
conditions
ating
Optimizing a high dense concrete mixture 55
4. Optimizing a high dense concrete mixture
4.1 Introduction
When a concrete wall subjected to hydrothermal cycles, water and vapour try to penetrate the wall.
The penetration rate depends mainly on the temperature and pressure of the water and vapour as
well as on the microstructure, durability and porosity of concrete. The aggregate, the matrix, and
the interface between them affect concrete porosity, microstructure and durability. The matrix
depends not only on water/cement ratio but also on the granulometry and reactivity of the
cementitious material. Therefore, in this research, concrete mixture optimization is primarily based
on three fundamental mechanisms:
1‐ Maximizing the packing density of solid particles.
2‐ Designing a dense cement matrix.
3‐ Densifying the interfacial transition zone.
Unlike normal concrete, it is no longer sufficient to base the mix composition on the principle of
compressive strength and w/c ratio relationship. For the sake of developing high dense concrete,
the above mechanisms has been optimized. In this chapter, detailed description of these
mechanisms and their influence on concrete performance and properties will be introduced.
Moreover, explanation of how these mechanisms can be optimized will be given. In addition, the
design and composition of 23 different mixes will be presented. The packing density of all concrete
mixes has been calculated using Rene LCPC software which based on the compressible packing
model (CPM). For these calculations, the packing density of all concrete constituents has been
measured and used as input for this model. At the end of this chapter, the measured properties of
fresh concrete including workability, air content and density will be presented and discussed.
4.2 Maximizing the packing density of solid particles
Excellent concrete can be made with a wide range of aggregate grading. Obviously, there are limits
of grading outside which it is not possible to make good concrete, but by choosing homogeneously
graded mixtures, it is possible to achieve the desired concrete mix within the desired borders. The
concrete mixture volume composed generally of about 65 – 80 % of aggregate and about 15 – 30 %
of water and binder [Rached, 2009]. The importance of aggregate gradation can be clarified by
considering concrete as a softly compacted cluster of aggregate particles bonded together with
cement paste [Mindess, 2003]. The properties of aggregate have crucial effects on the performance
of fresh and hardened concrete. The chemical composition of the aggregate is usually less important
than the physical characteristics, such as volume, shape, size, and grading. Therefore, the aggregate
should be chosen mainly on the base of its physical properties and to a lesser extent on its chemical
Optimizing a high dense concrete mixture 56
characteristics. The proper sieve distribution and packing of aggregate particles, together with other
particles in the mix, is the direct and systematic way to ensure the high density of hardened
concrete. Spherically shaped grains are considered as more advantageous compared to the angular
shaped aggregates. The porosity increases from 40 to 60 % when the angularity factor of aggregate
is doubled [Nehdi, 1998]. Round materials like gravel give a denser concrete than broken stone
[Fuller, 1907]. The maximum grain diameter should be accurately chosen to improve workability and
to reduce stress concentrations. Increasing the maximum aggregate size is considered as an
advantage for some concrete properties and a disadvantage for some others. Increasing the
maximum aggregate size reduces the paste requirement for the mix. Moreover, the smaller the
average size of aggregate, the lower the packing of aggregate [Powers, 1968; Mindess, 2003].
However, large aggregate sizes increase the internal stresses and this tends to reduce the strength.
Nevertheless, Larrard stated that with an aggregate size of 25 mm it is possible to produce high
performance concrete with compressive strength up to 130 MPa at 28 days [Larrard, 1999]. Results
of studies on the effect of the maximum aggregate size on the strength of HPC are mixed. Large size
aggregates can reduce the water demand, which leads to a considerable increase in concrete
strength. On the other hand, the use of small size can eliminate internal defects in aggregate
particles and results in a smaller cement paste/aggregate transition zone, which enhances the
concrete mechanical properties. However for HPC, the aggregate/cement paste bonding must be
strong enough to transfer significant stress to the aggregate. The failure going through the
aggregate particles are commonly observed on the surfaces of HPC specimens. Hence, the aggregate
can become the weak link, and may represent the limiting factor for the strength of the concrete.
On the other hand, concrete durability can also be improved with increasing the maximum aggregate
size because there will be less paste subjected to the chemical or physical attack [Mindess, 2003].
In this research, the concrete mixture proportioning is based on the granular optimization of solid
content by means of the Ideal Fuller curve (Figure 4.1). Compared to the well‐known Fuller parabola
for the highest density of aggregate, the Ideal curve has a higher content of fines and a lower coarse
aggregate content as can be observed in Figure 4.1. The packing density and the concrete mixture
proportioning will be calculated on the basis of the grading of all concrete constituents, not only the
aggregate grading. Brouwers stated that whilst the packing of the aggregate plays a major role, the
packing of all solid particles in the concrete mix should be the basis for the mix design [Brouwers,
2005]. In this investigation, in order to reduce the water demand and cement content, and at the same
time to hold the micro‐cracks as low as possible, the maximum grain size was taken as 16 mm. According
to the Ideal Fuller curve, the required aggregate volume (d > 125 µm) is 85.13 %, whereas the fine
materials content (d < 125 µm) is 14.87 % by volume.
Optimizing a high dense concrete mixture 57
Figure 4.1: The grading curve of aggregates and binder according to Ideal Fuller curve According to [Fuller, 1907]
Figure 4.2: Comparison of Ideal Fuller with the standard grading lines of aggregate According to DIN 1045-2
Figure 4.2 shows the grading of aggregate according to Ideal Fuller curve compared to standard
areas A, B, and C according to DIN 1045‐2. It is clear that, the curve has a little bit higher coarse
aggregate content than the grading line A (from 4 to 16 mm), however, at lower sizes, the curve has
higher fine material content (< 2 mm). These fines are needed to maintain good cohesion and to
prevent segregation. In the fresh state, high powder content is necessary for a stable fresh concrete
that does not segregate during installation and in which the coarse aggregate does not settle after
compaction [Nischer, 2007]. The better the particle size distribution of concrete mixture, the lesser
the required powder for a stable fresh concrete. The increase in powder will improve the stability of
fresh concrete only when it does not adversely alter the particle size distribution in the powder
9.53 12.0114.87
18.5423.29
29.1435.22
44.47
62.98
4.49 6.25 8.8412.5
17.6825
35.36
50
70.71
100
0
10
20
30
40
50
60
70
80
90
100
0.03125 0.0625 0.125 0.25 0.5 1 2 4 8 16
Passing % (volume)
Size (mm)
Ideal Fuller curve
Fuller parabola
88
74
62
49
34
18
7
76
56
42
32
20
85
60
36
2112
832
100
3030
30
56.5
34.77
23.916.769.9
4.3130
10
20
30
40
50
60
70
80
90
100
0.0625 0.125 0.25 0.5 1 2 4 8 16
Passing % (Volume)
Size (mm)
C
B
A
U16
Ideal Fuller
Optimizing a high dense concrete mixture 58
range. However, high amounts of particles smaller than 0.001 mm (e.g. micro silica) in concrete
frequently do not lead to an improvement in fresh concrete stability, because in this case, large
amount of water and/or superplasticizer is required.
In this investigation, to get a good size distribution, the skeleton of aggregate size fractions should
be viewed as a whole rather than two separate entities; coarse and fine aggregate. The combination
of well graded coarse aggregate and well graded fine aggregate considered separately does not
necessarily result in a well graded aggregate mix. Coarse and fine aggregate as they come from the
quarry do not normally have size distributions that fit the dense packing curve. So, the addition of
“correcting” aggregates could help to reduce excesses or deficiencies in some sizes [Quiroga, 2003].
Because of the bad grading of the natural aggregates, it is difficult to achieve the highest packing
density as can be seen in Figure 4.3. It is obvious on the curve that there are some gaps between the
concrete mixture and the Ideal Fuller curve. Sometimes the mixture is higher as in the range of 0.5 ‐ 2
mm, therefore in the mixes preparation, sieve analysis of aggregate was done and the required amount
of each size has been taken. On the other hand, the mixture has lower content of particles in the size
range 0.063 ‐ 0.25 mm, therefore, quartz sand and quartz powder has been added to close this gap.
Figure 4.3: The grading curve of non-optimized concrete mixture and the Ideal Fuller curve
4.3 Designing a dense cement matrix
4.3.1 Introduction
Concrete can be considered as a composite material whose microstructure is randomly arranged.
It consists mainly of aggregate and cement paste and in between the interfacial transition zone
0
10
20
30
40
50
60
70
80
90
100
0.03125 0.0625 0.125 0.25 0.5 1 2 4 8 16
Passing % (volume)
Size (mm)
Ideal Fuller curve
Mixture without optimization
Optimizing a high dense concrete mixture 59
(ITZ). Similarly, cement matrix can also be considered as a random composite material, made up
of unreacted cement, C‐S‐H, CH, capillary pores, and other chemical phases [Hilsdorf, 1995].
Properties of cement matrix, particularly porosity and microstructure have a great influence on
the durability and strength of concrete. All transport processes depend primarily on the properties
and structure of the hydrated cement paste [Neville, 2004], which are related mainly to its
porosity and pore size distribution. The latter relies on the packing density of the cement particles
and fine materials as well as on the filling ability of the hydration products. The reduction in pore
size results in a significant decrease in transport properties like water permeability and ionic
diffusion, which are often the rate limiting properties in chemical attack. In addition to the
durability, the strength of concrete is fundamentally a function of the volume of voids in it
[Neville, 2004]. The strength of the cement matrix is governed by the packing density and the
homogeneity of the cement particles and fine materials; an increase of 40 % in strength could be
obtained just by adjusting the particle size distribution of the cement [Nehdi, 1998]. The strength
and durability of concrete depend essentially on the dense packing of cement matrix as well as on
the hydration products characteristics. The effect of these two parameters on cement and
concrete properties will be explained in the following sections.
4.3.2 Dense packing of cement matrix
Understanding the filling mechanism of particles can help to design durable high performance
concrete mixture with high density. The packing density of cement powder alone is relatively low
because of its narrow particle size distribution which makes the inter‐particle voids bigger. Systems
with the same particle sizes have high porosity and low density. The use of various fine materials
with different particle size distributions such as quartz powder, fly ash and silica fume largely affects
the voids content within the cementitious materials mixture. The efficiency of these materials in
filling up the voids or in improving the packing of the system is dependent mainly on their fineness
and particle shape. In general, a broader range of particle size distribution would yield higher
packing density. This is because with a broader range of particle size distribution, the medium
particles would fill up the voids between the large particles, and the fine particles would fill up the
voids between the medium particles and the very fine particles would fill up the voids between the
fine particles and so on, leading to the removal of more voids by the successive filling effect. Particle
system with a larger range of particle sizes can pack together in more efficient way than one with a
smaller range and as a result less space for water is remained [Moosberg, 2004]. Furthermore, the
improved gradation of the binder particles provides a lubrication effect through decreasing
aggregate interlocking.
Optimizing a high dense concrete mixture 60
On the other hand, the addition of too much filler may have a reveres effect on the system due to
the reduction of the packing density. The reason for that lies in the high surface area of these fillers
which need more water to maintain the required workability. However, in order to prevent the
flocculation and reduce the amount of mixing water, superplasticizer which has dispersing
properties shall be used. Superplasticizer is more efficient in a dense particulate system with high
surface area, and has only limited effect in a porous low‐density system. A combination of an
appropriate superplasticizer dosage to ensure optimal dispersion of fine particles and an
appropriate filler content to fill up the voids between bigger particles, can dramatically enhance the
packing and densify the microstructure of HPC.
4.3.3 Hydration products characteristics
The structure of hardened cement paste is created after the transition from a fluid to a rigid phase
with the progress in hydration of cement components. It is a continuous process that starts after
mixing cement with water and lasts a long time with a decreasing rate. Hardened cement paste is
the product of the hydration process which fills the voids between aggregate grains and binds all
elements of the concrete microstructure together. During the hydration process, the size and the
continuity of the pores control the permeability of the hardening concrete. The hydration of
Portland cement produces generally about 50 to 70 per cent by volume of calcium silicate hydrates
(C‐S‐H) which are very good binding materials at normal temperature. In addition, calcium hydroxide
crystals (CH, also called portlandite) constitute about 20 to 25 per cent of the volume of solids in the
hydrated paste. In contrast to the C‐S‐H, calcium hydroxide is a compound with a definite
stoichiometry, Ca(OH)2. It tends to form as thin long crystals of hexagonal plates with size of tens of
µm across [Ramachandran, 1996]. The morphology usually varies from nondescript to stacks of
large plates, and is affected by the available space, temperature of hydration, and impurities
present in the system. Compared to C‐S‐H, the strength‐contributing potential of calcium hydroxide
is limited as a result of a considerably lower surface area. It is a very weak material that adds no
structural strength to concrete. The presence of large calcium hydroxide crystals reduces the
adhesion capacity, not only because of the lower surface area and correspondingly weak van der
Waals attraction forces, but also because they serve as preferred cleavage sites owing to their
tendency to form an oriented structure [Mehta, 2006]. Because of its increased crystallinity degree
and the high density, calcium hydroxide contains an extensive network of capillary pores. It is the
major factor responsible for the poor strength of the interfacial transition zone in concrete and the
initiation of micro‐cracks. Its presence contributes to increased porosity, efflorescence, decreased
aggregate/cement paste bond and decreased concrete durability [Lamond, 2006]. Calcium
hydroxide is a highly soluble material, thus, pastes that have a high content of calcium hydroxide are
likely to be more prone to leaching and efflorescence and to have a greater potential for
Optimizing a high dense concrete mixture 61
deterioration in severe environment [Mindess, 2003]. Leaching of calcium hydroxide provides a
point of entry for aggressive agents by increasing permeability and diffusivity, as well as weakening
the matrix. This leaching out creates several channels available for the ingress and penetration of
water and deleterious substances inside the concrete [Siddique, 2011]. Under severe continued
conditions, depletion of the calcium hydroxide destroys and breaks down the normal structure
of the hardened cement paste, resulting in softening of the mortar and poor strength of
concrete [Hewlett, 2003]. Regarding mechanical properties and durability, reducing the calcium
hydroxide content is considered as an advantageous because it has several detrimental effects
as mentioned above.
4.3.4 Optimizing a dense cement matrix
From the above discussion, it is clear that most of concrete problems come from cement paste.
Therefore, concrete durability can be improved significantly by using low amount of cement in the
mix. This can be achieved by applying packing density theory in the mix design. Using low cement
content helps to reduce the chemical contraction, and reduces the generation of hydration heat,
which could cause thermal cracking in the structural elements. More enhancements can be attained
by the use of cements containing blast furnace slag. These cements, in contrast to ordinary Portland
cement, show lower permeability, lower hydration heat, lower effective alkali content, and lower
steel corrosion. The beneficial effects of blast furnace slag arise from the significant decrease in CH
content. The slag retains the alkali and CH in its hydration products (i.e. C‐S‐H) which in turn lead to
formation of denser microstructure of hydrated cement paste. That mean more of the pore space
being filled with C‐S‐H than in Portland‐cement paste [Siddique, 2011]. Furthermore, the hydration
process of slag cement is very slow compared to ordinary Portland cement. Thus, the formed C‐S‐H
phases are strong and thick and the hydration heat is low, however, in the case of Portland cement,
the hydration heat is high, causing thermal cracking, and the formed C‐S‐H phases are long and thin.
Generally, the use of slag results in a hardened cement paste with denser microstructure and
smaller pore sizes than equivalent OPC paste, thus durability aspects; porosity, permeability and
ionic diffusivity, are notably reduced [Virgalitte, 1995].
The use of fine materials basically enhances the durability and strength of concrete. They affect the
concrete microstructure in different ways. On the physical level (filler effect), when the added
particles fill the voids between cement particles and thus improve the compactness of concrete
mixture. On the chemical level, the fine particles may provide nucleation sites for the growth of
hydration products. Consequently, the microstructure of concrete will be more homogenous and
denser. Further improvement could be gained if the filler itself is pozzolanic. Mineral admixtures
with pozzolanic activity such as fly ash and silica fume are used extensively for improving concrete
Optimizing a high dense concrete mixture 62
properties. The improvements in durability and mechanical properties result from the reduction in
calcium hydroxide content and changes in pore structure. The pozzolanic materials modify the
microstructure of hydrated cement matrix perfectly. It produces excess amount of the strength‐
forming hydrates, C‐S‐H. The increased content of C‐S‐H leads to more homogeneous and denser
microstructure. Moreover, in the pozzolanic reaction, the capillary water and the calcium hydroxide
are largely consumed, therefore, further reduction of capillary porosity occurred and hence more
densification of microstructure is achieved. In addition to fly ash and silica fume, quartz can be
considered an inert material, but finely ground quartz could also react if it has a very high surface
area. The solubility of quartz depends mainly of the temperature, particle size and the alkalinity of
the medium. It is reported that the dissolution rate of quartz is approximately 2 ‐ 3 times higher at
pH value of 12 compared to pH value of 7 [Moosberg, 2004].
In this investigation, in order to achieve dense and homogeneous cement matrix, it is suggested to
use CEM III/B 32.5 N‐LH/HS/NA with slag content of about 68 %. To evaluate the performance of this
cement compared to ordinary Portland cement, OPC with two different strength classes have been
used, CEM I 42.5 N, CEM I 32.5 R. Furthermore, to study the influence of slag content on the
behaviour and properties of concrete, slag cement CEM/III A 32.5 N‐LH/NA with lower slag content
(about 50 %) has been used. On the other hand, in order to enhance the packing density of cement
matrix, different fine materials have been implemented. Several pozzolanic materials with different
particle sizes, shapes, and reactivity including fly ash, fine fly ash (M10 and M20) and silica fume
have been implemented. Quartz sand and quartz powder were used as fillers to densify the matrix
and to close the gaps between cement and aggregates.
4.3.5 Optimization of water/binder ratio
The durability of concrete cannot be characterized with a uniform value, but the impermeability of
concrete against water and gases is always of the most crucial aspects. The transports of liquids and
gases, which can be harmful to concrete, occur exclusively through the capillary pore system of the
cement matrix. Accordingly, minimizing the volume of capillary pores is of vital importance for
concrete impermeability and durability. It is theoretically known that, capillary pores begin to form
at a water/cement ratio higher than 0.42 [Neville, 2004]. On the other hand, the added water should
be sufficient to achieve the required consistency class. Therefore, in this research, the water/binder
(w/b) ratio has been chosen in the range of 0.27 to 0.42. The effectiveness factor (k factor) is
assumed to be 0.4 and 1 for fly ash and silica fume respectively.
Optimizing a high dense concrete mixture 63
4.4 Densifying the interfacial transition zone
The interface is known as the region of direct contact between two materials or two phases [Brandt,
2009]. In general, interfacial transition zone is a region up to 50 µm wide around each aggregate,
containing higher porosity and larger pores than the bulk cement paste. According to Neville, the
microstructure of the interface zone consists of a thin layer of CH crystals, about 0.5 µm thick,
covers the surface of aggregate, behind which there is a layer of C‐S‐H with the same thickness
[Neville, 2004]. Moving further away from the aggregate, there is the main interfacial zone, with 50
µm thick. The properties of the interface are related mainly to the texture and roughness of the
particles surfaces, their purity, the ability of wetting of material with the other, volume fraction of
all components, type of aggregate, maximum and minimum size of aggregate, and the particle size
distribution of the constituents [Brandt, 2009]. The transition zone is the weakest link in concrete
under mechanical action, and the first micro‐crack starts in it before propagation from aggregate to
aggregate. It is also the favourite place for penetration of aggressive components. Therefore,
chemical and microstructural characteristics of the interfacial zone between paste and aggregate
have important influences on the durability and mechanical properties of concrete. The interface
zone occupies one‐third to one‐half of the total volume of hardened cement matrix in concrete and
its microstructure is totally different from that of the bulk hydrated cement paste [Neville, 2004]. It
has less unhydrated cement, lower density, high porosity. The pores are generally larger than those
formed in the bulk paste. It was also observed that, this region contains less C‐S‐H, large oriented
crystals of CH, and high concentration of ettringite [Mindess, 2003]. The morphology of the
transition zone in normal concrete includes large and continuous voids formed around the coarse
aggregate. The porosity of the transition zone is higher than that of the bulk cement matrix, it is
about 3 times higher than the bulk porosity. Within the interface zone, the porosity is higher near
the aggregate and decreases with increasing distance from the aggregate down to the bulk cement
porosity. The aggregate concentration plays a crucial role on the properties of the transition zone.
At low aggregate concentration, transport properties are dominated by the bulk cement matrix
properties. However, increasing the aggregate content tends to bind interfacial zone close together
and they become interconnected, which create continuous channel for gas and liquid movement. In
this case, the transition zone may act as short circuit for diffusion of ions.
The weakness and high porosity of this ITZ can be attributed to different reasons. One of these
reasons is the low packing density at this region. The particles cannot pack together in an efficient
way as in the case of free space. Since the aggregate is many times larger than cement particles,
aggregate surface appears locally flat to the surrounding particles. This inefficient packing causes
less cement and high porosity to be presented initially near the aggregate surface, and this
condition exists so even after hydration. The width of the interfacial transition zone depends then
Optimizing a high dense concrete mixture 64
mainly on median particle size of cement [Hilsdorf, 1995]. So, the use of coarse cement will increase
the thickness of the transition zone and also result in the presence of large pores in this region.
During mixing, dry cement particles are unable to pack efficiently around the aggregate surfaces.
Thus, less cement is present to hydrate and fill the original void in this zone. Therefore, the interface
zone has much higher porosity than the hydrated cement paste [Neville, 2004]. It is also observed
that, high concentration of large crystals of CH are found closed to the aggregate surfaces, where
local bleeding is considered to have been likely [Taylor, 1997]. Within the consolidation process,
large particles, depending on their size, shape, and surface texture prevent the homogeneous
distribution of water and lime in fresh concrete. Because of this localized wall effect, some water
tends to accumulate at the surface of coarse aggregate particles, as bleed water. Then, the local w/c
ratio in interfacial zone becomes higher than the w/c ratio in the bulk cement paste [Aïtcin, 2004]. It
contains products of cement hydration with larger crystals of CH but without any unhydrated
cement. The complete hydration of cement can be considered as an indication of the high w/c ratio
at the interface more than elsewhere, this supports the wall effect hypothesis [Neville, 2004]. In
addition to the poor packing density of particles on the aggregate surfaces, the one sided growth of
hydration products can be considered as one of the reasons for existence of this zone. In this zone,
the available porosity is filled with the hydration products, growing from one direction only, unlike
the bulk paste where the products grow inward from all directions. Although composed of the same
components and hydration products, the microstructure and properties of the transition zone are
different from the bulk cement paste. In fresh compacted concrete, water films cover the surfaces
of large aggregate particles. This is due to the high w/c ratio closed to the large aggregate than that
away from it. Therefore, ettringite and CH owing to form at the high w/c ratio. These crystalline
products in the vicinity of the coarse aggregate exist as relatively large crystals, which in turn form a
more porous microstructure than in the bulk cement paste [Mehta, 2006]. The aggregate grading
also plays an important role on the properties of the transition zone. During the compaction of fresh
concrete, segregation may occur in mixtures with poorly graded aggregate, accordingly, a thick
water film can be formed on the aggregate surfaces especially beneath the particles [Mehta, 2006].
Accordingly, a transition zone with high porosity is produced and consequently high concentration of
CH crystals aligns uniformly towards the aggregate surfaces.
The interfacial transition zone (ITZ) is generally weaker than either of the two main components of
concrete, namely, the aggregate and the bulk hydrate cement paste. Therefore, it has a greater
effect on the mechanical behaviour of concrete than it is reflected by its size [Mehta, 2006]. Because
of the high porosity of the ITZ, the strength is very weak and it represents the position where micro‐
cracks begin to appear [Neville, 2004]. It is also found that concrete toughness depends mainly on
the fracture toughness of aggregate‐cement paste interface and is less affected by the fracture
Optimizing a high dense concrete mixture 65
toughness of the hydrated cement paste [Hillemeier, 1977]. The differences between the
microstructures of transition zone and bulk cement matrix play an important role in determining the
mechanical properties of concrete [Aïtcin, 2004]. In ordinary concrete, the ITZ has less crack
resistance than either hydrated cement paste or the aggregate due to high concentration of large
crystals of calcium hydroxide which makes this zone as the weakest link in concrete. In addition, this
zone subjects to the greatest stress due to differences in elasticity and Poisson ratio between bulk
cement matrix and aggregate, thus the fracture occurs preferentially in this zone. Therefore, it has
the largest content of pores and micro‐cracks which affects the overall performance of concrete.
The effect of mineral admixtures on enhancing the microstructure of interfacial transition zone
depends substantially on their reactivity and particle size distribution, assuming an efficient
dispersion of fine particles [Hilsdorf, 1995]. The small sized pozzolanic mineral admixtures can
basically offset the wall effect whereas they have not any influence on the one‐sided growth
phenomena. Moreover, they offer an additional benefit by converting CH into larger volume of
pozzolanic C‐S‐H. The filler effect is assumed to be the result of the fine and spherical shape of fine
particles. These particles eliminate bleeding and can be packed efficiently at aggregate surfaces.
Thereby, they can prevent the formation of water filled voids around the aggregate. By substituting
cement with SF, slag, fine fly ash, a smaller transition zone with lower CH content can be formed.
The incorporation of fine pozzolanic materials modifies the microstructure of the transition zone to
be like that of the bulk cement matrix. By the addition of pozzolanic materials, the reaction with
calcium hydroxide starts very quickly and additional C‐S‐H is formed making the ITZ denser. It
increases also the internal cohesion of fresh concrete; reducing the bleed water and the
accumulation of bleed water beneath the coarse aggregate particles. As a result, CH concentration
at the paste aggregate interface is significantly reduced. In addition, the thickness of ITZ is reduced
as the amount of fine pozzolans increases.
In this research, in order to produce high performance concrete with dense interfacial zone, several
supplementary materials have been used and tested. Fly ash and fine fly ash (M10 and M20) have
been used as pozzolanic materials to strengthen the transition zone and to reduce its porosity. In
addition, silica fume was also used for the same target and to compare its influence with that of fly ash
and fine fly ash. As mentioned before, fine materials can enhance the packing at the aggregate
surfaces, but it does not have any role to modify the one‐sided growth of the hydration products.
Therefore, to reduce this effect, a certain sequence of adding the concrete constituents into the mixer
has been used as can be seen in figure 3.8. It is suggested that, after adding the aggregate, it is useful
to add some water (about 30 % of the mixing water) to moisten the aggregate surfaces and then adding
the fine materials. By this sequence, the fine materials stuck well to the aggregate surfaces and reduce
Optimizing a high dense concrete mixture 66
the porosity of ITZ and as a result the concentration of calcium hydroxide in this area will be
considerably reduced.
4.5 Mix design and mixes composition
Based on the above discussions, several mixes have been designed and tested. The following steps
have been applied in concrete mix design.
1. Determination of the maximum aggregate size considering its effect on water and binder
content as well as on the hardened concrete properties (in this research 16 mm).
2. Calculating the solid materials fractions using the Ideal Fuller curve (Figure 4.1) which applied for
both aggregate and binder (for 16 mm, aggregate content is 85.13 % and binder content is 14.87
% by volume).
3. Choosing the aggregate grading that fit the curve in order to achieve the maximum packing
density.
4. Selecting the cement type to control chemistry of the hydration products (CEM III/B was chosen,
and for comparison, CEM I and CEM III/A were also applied).
5. Optimization of the binder proportioning (< 0.125 mm) by using various supplementary
materials, type and content, in such a way that maximum packing can be attained
(granulometric viewpoint), meanwhile, dense and durable cement matrix microstructure as well
as thin and dense interfacial transition zone can be achieved (chemical viewpoint).
6. Determination of the required fillers addition (quartz sand and quartz powder) to fill the gaps
between the mixture and the targeted curve and to make the mixture fit the curve as exact as
possible.
7. Calculating the water content from rheological, physical and chemical points of view (w/b
0.42, in order to reduce the capillary porosity as low as possible).
8. Adapting the superplasticizer dosage, that is compatible with the used cement, to get the
required consistency, and to enhance the packing density of fine materials.
In order to achieve the target of this part, produce high dense concrete and compare the effect of
different cementitious materials on the properties of concrete, 23 mixes have been prepared. Table
4.1 shows the composition of all concrete mixes.
Optimizing a high dense concrete mixture 67
Table 4.1: Composition of concrete mixes
Mix
Cementitious materials composition (wt.%)
SP (wt.%)
Aggregatekg/m3
QP kg/m3
QS kg/m3
w/b ratio
Cement FA M20 M10 SF
Type %
1 CEM III/B 100 0.7 1854 46 84 0.42
2 CEM III/B 70 30 1 1854 46 84 0.42
3 CEM III/B 70 30 1 1854 46 84 0.42
4 CEM III/B 70 30 1 1854 46 84 0.42
5 CEM III/B 70 15 15 1 1854 46 84 0.42
6 CEM III/B 70 20 5 5 0.9 1854 46 84 0.42
7 CEM III/B 90 10 0.7 1854 46 84 0.42
8 CEM III/B 65 25 10 1.1 1854 46 84 0.42
9 CEM III/B 65 12.5 12.5 10 1 1854 46 84 0.42
10 CEM III/B 65 15 5 5 10 1 1854 46 84 0.42
11 CEM I 42.5 N 100 0.87 1854 46 84 0.42
12 CEM I 42.5 N 70 20 5 5 1 1854 46 84 0.42
13 CEM I 42.5 N 70 15 15 1.8 1854 46 84 0.42
14 CEM I 42.5 N 65 12.5 12.5 10 2.2 1854 46 84 0.42
15 CEM I 42.5 N 65 15 5 5 10 1.9 1854 46 84 0.42
16 CEM I 42.5 N 90 10 1.2 1854 46 84 0.42
17 CEM III/A 65 12.5 12.5 10 1.7 1854 46 84 0.42
18 CEM I 32.5 R 100 0.87 1854 46 84 0.42
19 CEM I 32.5 R 65 12.5 12.5 10 1.4 1854 46 84 0.42
20 CEM III/B 67 12.5 12.5 8 1.8 1887 45 86 0.36
21 CEM III/B 67 12.5 12.5 8 4 1947 48 88 0.27
22 CEM III/B 70 15 15 3 1885 47 86 0.36
23 CEM III/B 70 15 15 4 1947 48 88 0.27
FA: fly ash M20: fine fly ash M10: fine fly ash SF: silica fume SP: superplasticizer QS: quartz sand QP: quartz powder W/b: water/binder ratio
Optimizing a high dense concrete mixture 68
4.6 Measuring the packing density
In order to ensure the high density of concrete, the compressible packing model (CPM) developed
by Larrard has been used to predict the packing density of the concrete mixes in the dry state
[Larrard, 1999]. This model is based on the concept of virtual packing density and compaction index.
The virtual packing density is the maximum possible density which occupies the minimum space if
the particles have been placed one by one (ideal case). However, in practice it is impossible to
achieve this density, usually the particles are randomly placed depending of the applied compaction
energy. For example, the virtual packing density of a system of monodisperse spheres equals 0.74,
while the actual packing density that can be measured in a random mix is close to 0.60/0.64.
Therefore, the compaction index K is introduced. If K tends to infinity, the real packing density αj
tends to the virtual packing density. The compaction index (K) depends mainly on the type of
compacting and is independent on the properties of the tested material (table 4.2). Two interaction
effects have been considered in this calculation: the wall effect exerted by coarser grains and the
loosening effect exerted by the finer particles. The effect of particle shape and texture is indirectly
included via measuring the actual packing density experimentally. Rene LCPC, commercially
available software based on the compressible packing model, has been used to determine the
maximum density or the porosity of the dry mixture. This software can calculate the compaction
index for any mixture at a given porosity, or calculate the porosity of any mixture at a given
compaction index. According to Larrard, after measuring the packing density of many samples, the
error provided by this model is generally less than 1 % [Larrard, 1999]. The general equation of the
compressible packing model which represents the virtual packing density of a mixture of n number
of size classes with category i being the dominant is expressed as follow [Fennis‐Huijben, 2010]:
jj
iij
n
ijjj
iiji
i
j
iti
rarb ]1[)]1
1(1[11
1
1
(4.1)
Where:
ti = calculated virtual packing density of a mixture when size class i is dominant.
i = virtual packing of size class i.
rj = volume fraction of size class j.
n = number of size classes in a mixture.
j = the virtual packing density of size class j.
For a single size particle class i with actual packing density αj, which can be experimentally
determined (section 4.7), j can be calculated by the following equation:
)1
1/(kjj
(4.2)
Optimizing a high dense concrete mixture 69
The loosening effect aij and the wall effect bij can be calculated from the following equations:
02.1)1(1i
jij d
da
(4.3)
50.1)1(1dj
db i
ij (4.4)
Where
di is the diameter of dominant size class i.
dj is the diameter of particle class j.
tit
iinii
ni
rKK
/1/1
/11
(4.5)
The packing density of the mixture αt is determined indirectly from equation 4.5. Based on the
above equations, this model has been used to calculate the packing density and porosity of
polydisperse mix, from the knowledge of three parameters: packing density of monosized classes,
particle size distribution of the all components and compaction index (K). The particle size
distribution of fine and coarse aggregate has been determined using sieve analysis. However, the
particle size distribution of the fines has been measured using laser granulometry as discussed in
chapter 3. In addition, to calculate the packing density of the mixture it is required to determine the
actual packing density of each concrete component individually (αj).
Table 4.2: Compaction index (K) for different compaction methods according to [Larrard, 1999]
Implementation Loose Striking
with a rod
vibration Wet
packing
Vibration with
Comp. 10 kPa
Virtual
K 4.1 4.5 4.75 6.7 9 infinity
4.7 Measuring the actual packing density αj
The maximum packing density of dry particles can be determined according to EN 1097‐3 for loose
bulk density (which incorporates the shape and surface texture effects). External loads such as
consolidation and vibration can be also implemented in this method to determine the packing
density at a certain compaction level [Fennis‐Huijben, 2010]. This method is acceptable for coarse
and fine aggregates, where the gravitation forces and shear forces between particles are dominant.
However, for powders (< 125 µm), the inter‐particle forces become increasingly important. These
forces can cause agglomeration of particles, and lowering the packing density. Therefore, it is
important to measure the packing density under the same conditions as when the particles would
be used in concrete, with water. On the other hand, the addition of superplasticizer alters the
Optimizing a high dense concrete mixture 70
microstructure in two main ways [Larrard, 1999]. First, it deflocculates the fine particles and
enhances the packing density of the system. Also, it can lubricate the solid surface, thus reduce the
friction forces between particles. In this investigation, two methods were used to measure the
packing density of fine materials: thick paste method developed by Larrard as well as Puntke
method for measuring the water demand of fine materials. Details of these methods can be found in
[Larrard, 1999; Puntke, 2002]. After determining the water demand, the following equation is used
to calculate the maximum packing density αj for each material:
p
wj
M
M
1000
1000
(4.6)
Where, Mw is the mass of water (kg), Mp is the mass of the powder (kg) and ρ is the powder density
in kg/m3.
4.8 Results of packing density
4.8.1 Packing density of fine materials.
The measured packing densities of all materials (αj) were used as input for Rene LCPC software to
calculate the packing density of all mixtures. Figure 4.4 shows the results of the maximum packing
density measurements for fine materials according to Larrard (thick paste method). The wet packing
densities of all materials were measured twice; once without superplasticizer and once with
superplasticizer. The packing densities of all materials depend basically on shape, surface texture,
fineness and particle size distribution. Certainly, the addition of superplasticizer increases the
packing density for all materials as can be seen in Figure 4.4. This is attributed to the role of
superplasticizer in dissolving flocks and dispersing the particles, which results in a looser but more
homogenous particle packing. Due to the high inter‐particle forces, the particles cannot fill the
spaces of their own classes without excess of water or superplasticizer. Through its action on the
surface, superplasticizer can partially liberate the water that adsorbed as a surface layer, but does
not decrease the amount of free water. Thus, the dispersion influence of superplasticizer is more
manifest in dense particulate systems with high surface area, while in a porous low‐density system it
has a limited efficiency [Moosberg, 2004]. Compared to the results of the wet measurement, the dry
packing density is lower for all fine materials. The reason for that lies mainly in the influence of
inter‐particle forces which become higher as the particle sizes reduce. These forces can create
agglomeration of particles and as a result the packing density is reduced. This effect is more visible
in silica fume which consists of particles in the size range of 0.1 to 0.5 µm. In the dry state, silica
fume has the lowest packing density which is 20 %. In spite of its spherical shape, the packing
density of silica fume is not as high as that of fly ash. This can be explained probably by the
Optimizi
differenc
particle
because
nearly th
differenc
(M20) ha
the inter
superpla
the fine
prove fo
and silica
Figure 4
4.8.2 P
The pac
The inpu
packing
the max
packing
packing
attribute
10
20
30
40
50
60
70
80
Packing den
sity %
ing a high de
ces in the p
forces. On
of its partic
he same pro
ce is the pa
as lower pac
r‐particle for
asticizer, bec
particles fro
or that are th
a fume (SF);
4.4: Dry and
Packing de
king density
ut data for
density resu
imum packi
densities. T
density. Mi
ed to the ba
0
0
0
0
0
0
0
0
CEM I32.5 R
ense concret
articles size
the other
cle size and s
operties as th
article size. M
cking densit
rces are very
cause it cann
om lying clos
he results of
in which all
d wet packin
ensity of dry
y of all mixe
this softwa
ults of differe
ng density w
The addition
ix 2 with 30
all bearing e
CEM I42.5 N
CE3
Wet P.D
te mixture
s. It is thoug
hand, norm
spherical sha
hose of norm
Moreover, f
ty. Indeed, it
y strong. The
not totally d
se together
f the packing
l particles ha
ng densities
ry concrete
es was meas
re is in mas
ent mixes m
was 87.3 %.
n of normal
0 % fly ash
effect exerte
EM III A32.5 N
CEM 32.
D Wet P.D
ght that the
mal fly ash h
ape. The sam
mal fly ash b
fine fly ash
t is thought
ese forces ca
disperse all fi
in the dry s
g densities o
ave a spheric
(P.D) of the
e mixtures.
sured using
ss ratio for
made with bla
However, m
fly ash app
has the hig
ed by fly ash
IIIB.5
FA
D with superp
e lower the
has the high
me trend can
but with quit
(M10) with
that there i
ause a poor
ine particles
tate as well
of fly ash, fin
cal shape.
e used fine
Rene LCPC
all substanc
ast furnace s
mixes 2, 3, 4,
pears to be
ghest packin
h particles w
M 10
plasticizer
particle size
hest packin
n be observe
te lower pac
higher fine
s a particle
packing den
s. The inter‐p
as in water
ne fly ash (M
materials (s
software as
ces classes.
slag cement
, 5, and 6 w
more effec
ng density o
which reduc
M 20 S
Dry P.D
e, the bigger
g density, a
ed for fine f
cking density
eness than f
size limit be
nsity, even w
particle forc
‐fines suspe
M20), fine fly
size < 125 µ
s previously
Figure 4.5
t (CEM III B).
ith fly ash h
ctive in enha
of 88.4 %. T
ces the part
SF QP
71
r the inter‐
and this is
ly ash with
y. The only
ine fly ash
elow which
when using
es prevent
ension. The
ash (M10)
µm)
discussed.
shows the
. For mix 1,
ave higher
ancing the
his can be
icles inter‐
Optimizi
locking [
10 % silic
clumping
used [Ta
forces b
[Larrard,
even wit
more ef
variation
Figure 4
Figure 4
86.0
86.5
87.0
87.5
88.0
88.5
89.0
Packing den
sity %
8
8
8
8
8
8
8
Packing density %
ing a high de
[Hüsken, 201
ca fume rep
g of fine ma
aylor, 1997]
ecome impo
, 1999]. Sim
th fly ash ad
ffective than
n in the surfa
4.5: Packing
4.6: Packing
Mix 1
86.0
86.5
87.0
87.5
88.0
88.5
89.0
Mix 1
III
I
ense concret
12]. Howeve
placement ha
terials whic
. Silica fume
ortant and o
milarly, mixe
dition. Com
n fine fly as
ace area and
g density of
g density of
Mix 2 M
1 Mix 12
III‐FA III‐
I‐FA
te mixture
er, the additi
ad the lowes
h is favoured
e particles h
overcome th
es 7, 8, 9 an
paring the r
sh in enhan
d particles si
concrete m
concrete m
Mix 3 Mix
Mix 13
‐M20 III‐M1
I‐M20/10 I‐M
ion of silica f
st packing de
d to occur in
have sizes lo
he natural te
nd 10 made
esults of mix
cing the pa
izes.
ixes made w
ixes made w
x 4 Mix 5
Mix 14 Mix
10 III‐M20/10
M20/10‐ SF I‐FA‐M
fume reduce
ensity which
n pastes wit
ower than 1
endency of
with silica
xes 2, 3, 4 an
cking densit
with CEM II
with differen
Mix 6
x 15 Mix 1
III‐FA‐M20/10
M20/10‐SF I‐SF
ed the packi
h is 86.4 %. T
h SF even w
1 µm and at
spherical pa
fume have
nd 5 showed
ty. This can
I/B
nt cement
Mix 7 M
16 Mix 17
III‐SF III‐F
IIIM20/10‐SF
ing density.
This may be
when superpl
this level t
articles to pa
low packing
d that norma
n be attribut
Mix 8 Mix
Mix 18
FA‐SF III‐M20/10
I I‐
72
Mix 7 with
due to the
lasticizer is
he surface
ack closely
g densities
al fly ash is
ted to the
x 9 Mix 10
Mix 19
0‐SF III‐FA‐M20/
‐M20/10‐SF
/10‐SF
Optimizing a high dense concrete mixture 73
Figure 4.6 shows the results of packing density of the second series of mixes (11‐19) made with
different cements. For mixes 11‐16 made with the CEM I 42.5, the addition of normal fly ash
improves the packing density, while the mixture containing silica fume (mix 12) has lower packing
density. As mentioned for the first series, normal fly ash is more effective in packing than fine fly
ash. In this group, the poor compactability of silica fume affects the packing density of concrete
mixes. Cement type also has an important effect on the packing density of concrete mixture. Mix 11
made with CEM I has a higher packing density than mix 1 with CEM III/B. Both mixes have the same
aggregate and cement volume content. The differences are the particle sizes and surface areas of the
cements. So, it can be said that, at a given aggregate content and grading, particle size distribution and
particle shape of the binders govern the packing density of concrete mixtures.
4.8.3 Results of fresh concrete properties
4.8.3.1 Air content
The air content of concrete has an important influence on determining the concrete mechanical
properties and durability. In non‐freezing environment, the presence of air voids in concrete has
harmful effects on its properties. In case of high dense concrete, high resistance to freezing and
thawing may be achieved automatically (no need for air voids) because of the low amount of
freezable water inside the concrete and because of the high resistance to water penetration
[Hilsdorf, 1995]. So, for high performance concrete it is important to keep the air content as low as
possible, below 2 ‐ 3 % with regard to strength and permeability [Larrard, 1999]. After hardening,
the air bubbles form a large volume of coarse voids inside concrete microstructure. Like other voids,
these voids affect the pore system and make it continuous and vulnerable to penetration of water
and aggressive materials. Furthermore, the presence of these voids deteriorates the mechanical
properties of concrete. Every increase of 1 % of air content reduces the compressive strength by
about 5 % [Neville, 2004]. Modulus of elasticity is also decreased by the same degree as strength
with increasing the air content [Ramachandran, 1996]. The existence of air inside concrete is
basically a result of an incomplete consolidation. In addition, the air content is affected by the mixer
speed, the compaction and the amount of concrete being mixed [Mindess, 2003]. Moreover, mix
proportions, sand content, fine materials content, aggregate shape and texture, and grading has a
crucial effect on the air content. Cement content and fineness also have a notable influence on air
content; lean mixes have higher air than rich ones.
In this investigation, the air content test has been performed according to DIN EN 12350‐7. Results
of air content of all mixes can be found in Table 4.3. The experimental results showed that the
addition of fly ash has an important role in reducing the air content [Ramachandran, 1996].
However, the addition of silica fume to slag cement results in an increase in air content (mix 7). This
Optimizing a high dense concrete mixture 74
may be due to the high surface area of silica fume and slag cement which need more water or
superplasticizer to completely disperse. On the other hand, mixes with fine fly ash exhibited higher
air content than mixes with normal fly ash at a given cement type. This can be also attributed to the
quite large size of normal fly ash particles compared to that of fine fly ash, which in turn enhances
the compactability and packing of particles. For most mixes, the results of air content are in good
agreement with the results of packing density measured with Rene LCPC. Generally, it can be said
that all mixes have air contents lower than 3 % and the differences between air contents for most
mixes are small. The main reason for that could be the high packing density of all mixes due to
applying the Ideal Fuller curve.
4.8.3.2 Workability
Concrete workability can be considered as an indicator for the behaviour or performance of
concrete in fresh state. The ACI defined the workability as “that property of freshly mixed concrete
or mortar which determine the ease and homogeneity with which it can be mixed, placed,
consolidated, and finished” [Neville, 2004]. Several factors affect the concrete workability but the
water content is the most important [Neville, 2008]. In addition, other parameters such as maximum
grain size, aggregate grading, texture and shape, cement fineness and content, and admixtures have
important influences on concrete workability. In this investigation, the flow table test according to
DIN EN 12350‐5 has been used to measure the workability. The experimental results of all concrete
mixes are presented in Table 4.3. The measured flow diameters of all mixes are in the desired range
(F3 ‐ F4) according to DIN EN 206‐1. Regarding superplasticizer content, mix 1 with CEM III/B needed
around 2.2 kg/m3 of superpalsticizer to achieve flow diameter of 53 cm, whereas, mix 11 with the
same proportions but with CEM I needed 2.72 kg/m3 to get 49 cm. This increase in admixture
dosage (about 23 %) may be attributed to the presence of slag which improves the workability and
makes the mix more flowable and cohesive. Slag particles are smooth and therefore absorb little
water during mixing and thereby leave more water for enhancing the workability [Neville, 2004]. This
effect is repeated in all mixes with slag cement when they are compared to mixes with Portland
cement.
Due to its spherical shape and its high compactability, normal fly ash mixes have high flowability
even with low superplasticizer dosage and water content. In spite of taking the effective factor as 1
and 0.4 for silica fume and fly ash, mixes with silica fume required more superplasticizer to achieve
the required consistency class. This is because the very large surface area of silica fume particles
needs a lot of water to be wetted and therewith increase the water demand and superplasticizer
amount. Nehdi explained the effect of silica fume on the workability on two opposite effects [Nehdi,
1998]. First, it works as filler because of its spherical shape and very small particles. The fine
Optimizing a high dense concrete mixture 75
particles fit into the void spaces between the relatively coarser cement grains and liberate the water
which fill this voids. Now this water participates to fluidize the concrete. On the other hand, as
mentioned above, silica fume particles tend to adsorb water because of their high fineness which
increases the water demand. Besides this explanation, another effect can be added that is the low
packing ability of silica fume particles which also increases the water demand. The experimental
results indicate that mixes with higher packing densities exhibit better workability. This is because of
the efficient packing of particles with different sizes. The successive filling of different classes make
the particles to displace the water molecules, thus the captured water between flocculated cement
particles can be released and participate in fluidizing the mix.
4.8.3.3 Density of fresh concrete
The density of fresh concrete has been determined by weighing a compacted known‐volume of
concrete according to European standards DIN EN 12350‐6. As the water is the lightest component
in concrete, the density is controlled basically by the water content. In addition, the density and
contents of other components have also important influences on fresh concrete density. It is clear
from the results that mixes 20 ‐ 23 with lower water content have the highest densities. On the
other hand, because of the higher bulk density of Portland cement (3.17 t/m3) compared to slag
cement (2.96 t/m3), mixes composed of OPC have higher density. However, mixes with silica fume
have the lowest density. This may be explained by the poor compactability of silica fume as
discussed before. In general, from the experimental results of concrete density, all mixes have a fresh
density higher than 2.4 t/m3. This can be explained by the high packing density of all solid materials
as a consequence of applying the Ideal Fuller curve. In addition, according to this curve, a high
content of aggregate is required and a lower amount of cement paste is needed to achieve the
maximum packing density. Thereby, the resulting mixes have high densities because of the relatively
high density of aggregate (about 2.61 t/m3) and the comparatively low density of the paste (about 2
t/m3). Furthermore, the reduction of the paste volume reduces the water demand which is one of
the major factors determining the concrete density. Finally, it can be said that the results of the
fresh concrete density agree well with the results of the packing density measured with Rene LCPC.
Optimizing a high dense concrete mixture 76
Table 4.3: Results of fresh concrete properties
Mix SP content (Kg/m3) Flow diameter (cm) Air content % Fresh density (t/m3)
1 2.2 53 1.5 2.43
2 2.19 52 1.3 2.45
3 3 48 1.6 2.45
4 3 51 1.4 2.46
5 3 51 1.3 2.46
6 2.6 54 1.3 2.44
7 2.54 48 2.3 2.42
8 3.1 50 2 2.44
9 2.8 50 2.2 2.45
10 3 50 2 2.44
11 2.72 49 1.4 2.46
12 2.19 50 1.6 2.48
13 3.94 50 1.9 2.47
14 4.47 48 1.3 2.46
15 3.86 49 1.3 2.46
16 3.36 49 1 2.43
17 3.52 54 1.45 2.46
18 2.68 52 1.5 2.45
19 3.01 46 1 2.46
20 3.83 49 1.2 2.47
21 8.78 44 1.5 2.50
22 6.75 49 1.5 2.47
23 8.83 48 1.4 2.49
Results and discussion of the optimized concrete properties 77
5. Results and discussion of the optimized concrete properties
5.1 Introduction
In this chapter, mechanical properties, porosity and durability of the optimized concrete mixes are
presented and discussed. Experimental results of mechanical properties including compressive
strength, splitting tensile strength and modulus of elasticity are given. The results indicated that
most concrete mixes exhibited compressive strength higher than 60 MPa which reflected the
important role of enhancing the packing density. Moreover, the modulus of elasticity was higher
than 40 GPa for all mixes which demonstrates the high efficiency of concrete mixture optimization
in strengthening the interface zone between cement paste and aggregate and reducing the
probability of micro‐cracking. A modulus of elasticity of about 50 GPa has been attained with low
w/b. In addition, the concrete porosity was measured using three different methods; water porosity,
helium pycnometry and mercury intrusion porosimetry (MIP). Furthermore, the MIP method has
been used to study the pore size distribution and to calculate the capillary porosity which is
responsible for the transport properties of concrete. The porosity of concrete made with blended
cement is lower and the pores are finer than those made with ordinary Portland cement. The results
of porosity pointed out that concrete made with fine fly ash showed very low porosity. However, at
low w/b ratio, combination of fine fly ash with silica fume resulted in the lowest porosity, about 3 %,
which is comparable to that of UHPC. Moreover, the capillary porosity was very low (about 2 %)
which is advantageous with regard to concrete durability.
The durability of concrete has been evaluated via measuring the transport properties of concrete
which related directly to its resistance to aggressive attack. Transport of contaminants into concrete
can take place through three mechanisms; permeation, diffusion and absorption. Therefore, the
resistance of concrete against these mechanisms were measured and assessed. The experimental
results of water penetration depth indicated that most of concrete mixes have a very low
penetration depth. On the other hand, the use of fine pozzolanic materials resulted in concrete with
more dense and homogeneous microstructure due to both filler and pozzolanic effects. As a result,
the resistance to chloride attack is significantly increased. Additionally, the transition zone between
aggregate and cement matrix which is the locus of coarse pores became denser due to the
consumption of calcium hydroxide crystals by the pozzolanic reaction. The capillary suction results
also showed very low absorption coefficient especially for mixes with pozzolanic materials and low
w/b ratio. Compared to literature, the optimized concrete showed desirable performance
concerning durability and permeability. Because of the much data from the experimental
investigation, some results are presented and discussed in this chapter, while other data and tests
results are given in the appendices.
Results a
5.2 M
5.2.1 C
The com
ages of 2
concrete
is the w/
MPa at
mixes. In
especial
ages is h
becomes
days, the
was 62 M
Figure 5
The add
dependin
cement
results o
addition,
has com
ash, conc
ages of 2
2
4
6
8
10
12
Compressive stren
gth (MPa)
and discussio
Mechanical
Compressi
mpressive str
28 and 91 d
e mixes. It is
/b ratio. Mix
28 days and
n addition,
ly at early a
higher than
s to be nea
e compressi
MPa. Howev
5.1: Compre
ition of poz
ng on their
enhances th
f mixes 9 an
, the use of s
pressive stre
crete made w
28 and 91 da
0
20
40
60
80
00
20
Mix 1
Fc 2
Fc 9
III
on of the op
l propertie
ive strength
rength of th
days accordin
s clear on th
xes 21 and 2
d 99 and 94
the cement
ges (28 days
the strengt
rly the sam
ve strength
er, at 91 day
essive stren
zzolanic mate
type, conten
he strength o
d 19 which h
silica fume r
ength of 78 M
with silica fu
ays. The stren
Mix 2
28
91
III‐FA
ptimized con
es
h
he concrete
ng to DIN EN
e figure tha
23 with w/b
4 MPa at 91
t type has a
s). It is well
h of slag ce
e. The resu
of mix 1 wi
ys both mixe
gth of differ
erials has an
nt and prop
of concrete
have compre
esulted in an
MPa which is
ume or fine f
ngth develop
Mix 5 MIII‐M20/10
ncrete prope
samples ha
N 12390‐3. F
t, the main
ratio of 0.27
1 days respe
also an imp
known that
ment, while
lts of mixes
th slag ceme
s exhibited r
rent concret
n important
perties. Comb
more than
essive streng
n improveme
s higher than
fly ash or a c
pment of mix
Mix 7 Mix
III‐SF III‐M20
erties
ve been de
Figure 5.1 sh
factor that c
7 exhibited c
ectively, wh
ortant role
the develop
e at later ag
s 1 and 18 c
ent was 52
roughly simil
e at 28 and
t influence o
bination of p
with slag ce
gth of 71 and
ent in compr
n mix 1 by ab
combination
x 2 with norm
x 9 Mix 18
0/10‐SF I
termined us
hows the te
controls the
compressive
hich are the
on the dev
pment of str
ges the final
confirmed t
MPa, while
lar strengths
91 days
on concrete
pozzolanic m
ement as ca
d 82 MPa at 9
ressive stren
bout 15 %. C
of both sho
mal fly ash is
8 Mix 19
I‐M20/10‐SF
sing 100 mm
st results fo
compressiv
e strength of
highest am
velopment o
rength of OP
compressiv
his assumpt
for mix 18 w
s (70 ± 2 MPa
compressive
materials wit
n be noticed
91 days resp
ngth as expec
Compared to
wed higher
s very slowly
Mix 21
III‐M20/10‐SF
78
m cubes at
or different
ve strength
f 82 and 80
mong other
of strength
PC at early
ve strength
tion. At 28
with OPC it
a).
e strength;
th Portland
d from the
pectively. In
cted. Mix 7
o normal fly
strength at
y compared
Mix 23
III‐M20/10
Results a
to other
Figure 5.
compres
only at t
exhibited
5.2.2 S
In spite
valuable
The expe
w/b rati
results o
exhibited
tensile s
0.42 and
Figure 5
Accordin
strength
Where ft
shows th
obvious t
Splitting tenslie stren
gth M
Pa
and discussio
mixes with
1. At low w/
ssive strength
he same w/b
d similar com
Splitting ten
of the defin
e especially r
erimental re
io, packing
of tensile str
d higher te
trength of c
d reached 6
5.2: Splitting
ng to Nevill
h is governed
t is the splitti
he experimen
that, the rela
0
1
2
3
4
5
6
7
Mix 1
III
on of the op
different po
/b ratio (0.27
h of mix 21
b ratio (0.27
mpressive stre
nsile streng
nitive impor
regarding th
esults showe
density, cem
rength mea
ensile streng
concrete. The
MPa for mix
g tensile stre
e [Neville, 2
d by the follo
ft = 0.3 fc
ing tensile st
ntally deduce
ationship bet
Mix 2
III‐FA II
ptimized con
ozzolanic ma
), silica fume
with silica fu
). However,
ength as mix
gth
rtance of co
he cracks dev
ed that like c
ment type,
sured at ag
gth. Howev
e tensile stre
xes with w/b
ength of diff
2004], the
owing formu
c 2/3
trength and f
ed relationsh
tween the m
Mix 5 M
I‐M20/10 I
ncrete prope
aterials, part
e looked to b
ume and fine
at w/b ratio
x 5 with fine f
mpressive s
velopment a
compressive
and supple
e of 91 day
er, the add
ength range
b ratio of 0.2
ferent concr
relationship
ula:
fc is the com
hip between
measured resu
Mix 7 Mix
II‐SF III‐M20/
erties
icularly at ea
be more effec
e fly ash is h
o of 0.42, mix
fly ash only.
strength, kno
and failure m
e strength, te
mentary ma
ys. It is clear
dition of po
es from 3 to
27.
rete at age o
p between t
mpressive stre
tensile stren
ults agree wi
9 Mix 18
10‐SF I
arly ages as
ctive in enha
higher than m
x 9 with fine
owing the t
modes of co
ensile streng
aterials. Figu
r that mixes
ozzolanic ma
5 MPa for m
of 91 days
tensile stren
(5.1)
ength of con
ngth and com
ith theoretica
Mix 19
I‐M20/10‐SF
can be clea
ncing the str
mix 23 with f
e fly ash and
ensile stren
oncrete [Nev
gth depends
ure 5.2 illus
s with lower
aterials enh
mixes with w
ngth and co
ncrete (MPa)
mpressive str
al ones to lar
Mix 21 M
III‐M20/10‐SF II
79
arly seen in
rength. The
fine fly ash
silica fume
ngth is also
ville, 2004].
s mainly on
strates the
r w/b ratio
hances the
w/b ratio of
ompressive
. Figure 5.3
rength. It is
rge extent.
Mix 23
II‐M20/10
Results and discussion of the optimized concrete properties 80
Figure 5.3: Relationship between compressive strength and splitting tensile strength
5.2.3 Modulus of elasticity
From structural point of view, measuring the elastic modulus of concrete is very important in order
to design concrete elements to resist structural loads, moments and deflection. Although concrete is
non‐elastic material, determination of the elastic modulus is important to predict the stresses
generated by strains due to environmental effects. The elasticity of any material depends mainly on
the fractions and properties of its components. Aggregate content and properties, cement matrix
properties and transition zone features are the main factors influencing concrete elasticity. In this
research, the modulus of elasticity has been determined according to DIN 1048‐5 at age of 91 days.
The experimental results of elasticity modulus are found in Figure 5.4. It is obvious that, all mixes
have modulus of elasticity of more than 40000 MPa. Mix 21 with w/b ratio of 0.27 has the highest
elasticity, about 51000 MPa. Mix 1 and mix 18 showed roughly the same elasticity modulus (about
43000 MPa), that mean slag cement and OPC have the same effect on concrete elasticity as
mentioned by [Virgalitte, 1995].
Modulus of elasticity of concrete is related directly to its compressive strength as can be seen in
Figure 5.5. Both are affected by the porosity and density of concrete although not to the same
degree. At low w/b ratio, with the addition of fine materials, the porosity of concrete was decreased
while the strength and elasticity are increased. Moreover, the transition zone between cement
paste and aggregate becomes denser which results in more improvement in strength and elasticity.
According to Mehta et al. [Mehta, 2006], the relationship between compressive strength and
modulus of elasticity is governed by the following formula for normal weight concrete:
0
2
4
6
8
10
50 60 70 80 90 100 110
Splitting tensile stren
gth (MPa)
Compressive strength (MPa)
Experimental
Theoretical
Results a
Where fc
Figure 5
modulus
compres
Figure 5
Figure 5
10
20
30
40
50
60
Modulus of elasticity (MPa)
and discussio
cm and Ec are
5.5 shows t
s of elastici
ssive strengt
5.4: Modulus
5.5: Relations
0
0000
0000
0000
0000
0000
0000
Mix 1
10
20
30
40
50
60
Modulus of elasticity (MPa)
III
on of the op
Ec =2.15 *
e the averag
he relations
ty. It is cle
h and modu
s of elasticit
ship betwee
1 Mix 2
0
0000
0000
0000
0000
0000
0000
60
III‐FA
ptimized con
104 (fcm/10)1
ge compressi
ship betwee
ear that the
lus of elastic
ty of differen
en compress
Mix 5
70
III‐M20/10
ncrete prope
1/3
ive strength
en theoretic
e relationsh
city agreed w
nt concrete
sive strength
Mix 7 M
80
Compressiv
III‐SF III‐M2
erties
and modulu
cal and mea
hip between
well with the
at age of 91
h and elastic
Mix 9 Mix 1
90
ve strength (M
E
T
20/10‐SF I
(5
us of elasticit
asured com
n the exper
theoretical
1 days
modulus of
18 Mix 19
100
MPa)
Experimental
Theoretical
I‐M20/10‐SF
5.2)
ty in MPa re
pressive str
rimentally d
relationship
f concrete at
Mix 21
110
III‐M20/10‐SF
81
espectively.
rength and
determined
.
t 91 days
Mix 23
III‐M20/10
Results a
5.3 Po
5.3.1 P
Figure 5
21 and 2
Howeve
fine fly a
to mix 1
about 9.
about 9
porosity
Figure 5
5.3.2 W
In this m
realistic.
Figure 5
that the
pycnome
the dive
overall r
pycnome
0
2
4
6
8
10
12
Total porosity %
and discussio
orosity
Porosity me
.6 presents
23 with w/b
r, mix 18 wi
ash and 10 %
18 with OPC
.8 %. More r
%. Similarly
as can be se
5.6: Total po
Water poro
method, wat
. In this test
5.7 illustrate
porosities m
etry. This m
erse in the s
results. The
etry method
Mix 1
III
on of the op
easured wi
the experim
b ratio of 0
ith OPC only
% silica fume
C, the use of
reduction in
y, the incorp
een from the
orosity of co
osity (effect
er was used
method, co
s the exper
measured wi
may be due t
size of speci
porosity res
d.
Mix 2 M
III‐FA III‐M
ptimized con
ith helium p
mental result
.27 have ve
y has the hig
e (mix 19), th
f slag ceme
n the porosit
poration of
e results of m
oncrete mea
tive water p
d to calculat
ncrete speci
imental resu
ith water sat
to the differ
mens. Gene
sults of all co
Mix 5 Mix
M20/10 III
ncrete prope
pycnometry
ts of total po
ery low poro
ghest porosi
he total poro
nt (mix 1) le
ty has been
silica fume
mix 9.
asured with
porosity).
e the poros
imens were
ults of the t
turation are
rences in th
erally, these
oncrete mix
x 7 Mix 9
I‐SF III‐M20/
erties
ry
orosity of co
osities which
ty which is
osity is signif
eaded to a
achieved by
together w
helium pycn
ity of concre
cured unde
total porosit
quite highe
e methodol
differences
es have the
9 Mix 18
10‐SF I
oncrete mixe
h are 3.6 an
11 %. By rep
ficantly redu
quite decre
y the additio
with fine fly
nometry at 9
ete, which m
r water unti
ty at age of
er than that
ogies of the
s are small a
same trend
Mix 19
I‐M20/10‐SF
es. As expec
nd 4.2 % re
placing OPC
uced to 7 %.
ase in the p
on of fly ash
ash reduced
91 days
make the re
l the day of
f 91 days. It
measured w
e two tests
and did not
d as that in t
Mix 21
III‐M20/10‐SF
82
cted, mixes
spectively.
with 25 %
Compared
porosity to
(mix 2) to
d the total
sults more
testing.
is noticed
with helium
along with
affect the
the helium
Mix 23
III‐M20/10
Results a
Figure 5
5.3.3 P
Figure 5
at age o
concrete
on concr
tradition
w/b rati
[Teichma
and mic
capillary
framewo
sheet of
Figure 5
and 23 w
On the o
0
2
4
6
8
10
12
14
Total porosity %
and discussio
5.7: Total por
Porosity an
.8 presents
of 91 days. T
e. In additio
rete porosity
nal concrete
o (21 and 2
ann, 2004].
crostructure
y porosity is
ork. Therefo
f MIP measu
.9 shows the
with w/b rat
other hand m
Mix 1
III
on of the op
rosity of con
nd pore siz
the experim
The results c
n, concrete
y. Compared
e which lies
23) exhibite
Undoubtedl
of concret
of most con
ore, the cap
rements. It
e experimen
tio of 0.27 h
mix 18 with w
Mix 2 M
III‐FA III‐M
ptimized con
ncrete measu
ze distributi
mental resul
confirmed t
component
d to literatu
between 15
d porosity i
ly, measurin
te. Howeve
ncern. Most
illary porosi
is assumed
ntal results o
have very low
w/b of 0.42
Mix 5 M
M20/10 III‐
ncrete prope
ured with eff
ion measur
ts of the tot
hat w/b rat
ts proportio
ure, most of
5 to 20 % [T
n the range
ng the poros
er, regarding
transport m
ity of concre
to be in the
of capillary p
w capillary p
has the high
ix 7 Mix
‐SF III‐M20/
erties
fective water
red with M
tal porosity
io is the ma
ons and prop
these mixes
Teichmann,
e of UHPC w
ity gives a g
g durability
mechanisms
ete mixes ha
range of 30
porosity of d
porosity whi
hest capillary
9 Mix 18
10‐SF I
r method at
IP
of concrete
ain factor co
perties have
s have lowe
2004]. More
which is in t
ood indicati
y and deter
take place
as been calc
0 nm to 10 µ
different con
ich is 1.9 an
y porosity w
8 Mix 19
I‐M20/10‐SF
91 days
e specimens
ontrols the p
e important
r porosity th
eover, mixe
the range of
ion of the po
rioration of
via the capi
culated from
µm [Teichma
ncrete mixes
nd 2.96 % re
which is 5.6 %
Mix 21
F III‐M20/10‐SF
83
measured
porosity of
influences
han that of
s with low
f 4 to 6 %
ore system
concrete,
llary pores
m the data
ann, 2007].
s. Mixes 21
spectively.
%.
Mix 23
III‐M20/10
Results a
Figure 5
concrete
Figure 5
the size
5.4 D
5.4.1 P
5.4.1.1
The wate
Figure 5
revealed
concrete
0
2
4
6
8
10
12
Total porosity %
0
1
2
3
4
5
6
Capillary porosity %
and discussio
5.8: Total po
e mixes at a
5.9: Capillar
range of 30
urability
Permeabili
Water pen
er penetrati
5.10 illustra
d that all m
e can be con
Mix 1
Mix 1
III
III
on of the op
orosity of c
age of 91 da
ry porosity
0 nm to 10 µ
ity
netration de
on depth ha
tes the exp
mixes exhibit
nsidered imp
Mix 2
Mix 2
III‐FA II
IIIII‐FA
ptimized con
concrete me
ay
of concrete
µm
epth
as been mea
perimental
ted low per
permeable i
Mix 5 M
Mix 5 M
II‐M20/10 II
II‐M20/10 III
ncrete prope
easured with
e measured
asured accor
results of w
rmeability (
if the penet
Mix 7 mix
Mix 7 mix
I‐SF III‐M20/
‐SF III‐M20
erties
h mercury i
using the m
rding to DIN
water pene
depth < 20
ration depth
x 9 Mix 1
x 9 Mix 18
/10‐SF I
0/10‐SF I
intrusion po
mercury int
EN 12390‐8
etration dep
0 mm). Acco
h is lower th
8 Mix 19
8 Mix 19
I‐M20/10‐SF
I‐M20/10‐SF
orosimetry o
rusion poro
8 at the age o
pth tests. T
ording to N
han 50 mm,
Mix 21
Mix 21
III‐M20/10‐SF
III‐M20/10‐SF
84
of different
osimetry in
of 91 days.
The results
Neville, the
and if the
Mix 23
Mix 23
III‐M20/10
III‐M20/10
Results a
penetrat
aggressiv
permeab
penetrat
other ha
volume
penetrat
depth of
and whi
show th
penetrat
Figure 5
5.4.1.2
The tran
several p
type and
the conc
permeab
penetrat
properti
air perm
four tim
1
1
2
2
3
Water pen
etration dep
th (mm)
and discussio
tion is lowe
ve conditio
bility of con
tion depth w
and, the cem
and connec
tion depth o
f 18 mm. At
ch have pen
hat slag cem
tion depth o
5.10: Water
Air perm
nsport of ai
parameters.
d pozzolanic
crete age, cu
bility measu
tion depth,
es. It is obv
meability (3.4
es due to re
0
5
10
15
20
25
30
Mix 1
III
on of the op
er than 30
ns [Neville,
ncrete is th
which is abo
ment type an
ctivity whic
of 8 mm wh
the same ti
netration de
ment concre
of mix 1 was
penetration
meability
r via concre
The air per
materials co
uring, entrai
urements o
the results
ious that mi
4 x 10‐17 m2)
educing w/b
Mix 2
III‐FA
ptimized con
mm, then
2004]. The
he w/b ratio
ut 3 mm. Ho
nd mineral a
h control t
hich is lowe
me, mix 5 h
epths of 11 a
ete showed
15 mm, whe
n depth of th
ete occurs t
meability of
ontent and p
ned air cont
of concrete
reflected th
ix 21 prepar
compared t
b ratio from
Mix 5
III‐M20/10
ncrete prope
the concre
e results sta
o. Mix 21 w
owever, mix
admixture pr
he water p
er than mix
as lower de
and 13 mm
d higher res
ereas mix 18
he concrete
through the
f concrete d
properties. F
tent and tem
specimens
he major rol
red with w/b
to other mix
0.42 to 0.27
Mix 7 M
III‐SF III‐M2
erties
te can be
ated also th
with w/b r
x 23 has a pe
roperties ha
penetrability
2 with norm
pth than mi
respectively
sistance to
8 exhibited p
at age of 9
e connected
epends on w
Furthermore
mperature. F
at age of
le of w/b ra
b ratio of 0.
xes with w/b
7. However,
ix 9 Mix 1
0/10‐SF I
regarded as
hat the mai
atio of 0.27
enetration d
ave crucial in
y. Mix 5 wi
mal fly ash
xes 7 and 9
y. The result
penetration
penetration
1 days
pore syste
w/b ratio, ag
e, the air pe
Figure 5.11 s
91 days.
atio on dete
27 and silica
b ratio of 0.4
, mix 23 mad
18 Mix 19
I‐M20/10‐SF
s impermea
in factor go
7 showed t
depth of 5 m
nfluences on
th fine fly
and with p
made with
ts of mix 1 a
n than OPC
depth of 18
em which de
ggregate typ
rmeability d
hows the re
Similar to
ermining the
a fume has
42. It is redu
de with the
Mix 21
III‐M20/10‐SF
85
able under
overns the
the lowest
mm. On the
n the pores
ash has a
enetration
silica fume
and mix 18
C mix. The
8 mm.
epends on
pe, cement
depends on
esults of air
the water
e transport
the lowest
uced about
same w/b
Mix 23
III‐M20/10
Results a
ratio but
other ha
concrete
10‐17 m2
replacem
shown f
relatively
Figure 5
5.4.2 A
The capi
concrete
absorpti
increase
of mass
Figure 5
concrete
Where:
(from th
of calcu
0
2
4
6
8
10
12
14
16
Air permeability x 10‐17 (m
2)
and discussio
t without sil
and, the inco
e made with2) is around
ment of OPC
rom the res
y twice the a
5.11: Air per
Absorption
illarity of co
e. In this inv
on coefficie
e in the mass
was applied
.12 present
e mixes. The
absorpK
mtf is the v
he fitted line
lated absor
Mix 1
III
on of the op
lica fume ha
orporation o
h normal fly a
d two folds
C with silica
sult of mix 1
air permeab
rmeability of
n (capillary
ncrete has a
vestigation,
ent according
s of the spe
d at certain p
s the exper
e following e
ption
m
value of incr
on the figu
rption coeff
Mix 2
IIIII‐FA
ptimized con
as a little bit
of fine fly as
ash. The res
higher than
fume and
9. The air p
bility of mix 1
f different co
suction)
a very impor
the capillar
g to DIN EN
ecimen due t
periods of tim
imental mea
quation was
f
otf
t
mm
reased mass
re), and tf is
ficient of di
Mix 5 M
III‐M20/10
ncrete prope
higher perm
sh improved
istance of m
n mix 2 wit
fine fly ash
ermeability
19 (7.2 x 10‐
oncrete mea
rtant influen
ry suction te
ISO 15148.
to the rise o
me; at the b
asurements
s used to cal
s at the end
s the testing
ifferent con
Mix 7 Mix
III‐M20I‐SF
erties
meability (3.
the imperm
mix 5 with fin
th normal f
significantly
of mix 18 w17 m2).
asured at 9
nce on the in
est has bee
. The main i
of water by
beginning, 20
of the mas
lculate the w
of the test
period (hou
ncrete mixes
9 Mix 18
0/10‐SF I
.9 x 10 ‐17 m2
meability of
ne fly ash to
fly ash (9.7
y reduced t
was about 14
1 days
ngress of agg
en used to m
dea of this t
capillary for
0 minutes, 1
s increase w
water absorp
(5
(kg), mo is
urs). Figure 5
s. The rate
8 Mix 19
I‐M20/10‐SF
2) than mix
concrete co
air permeab
x 10‐17 m2
he air perm
4.3 x 10‐17 m
gressive mat
measure the
test is to me
rce. The mea
, 2, 4, 8, and
with time fo
ption coeffic
5.3)
the m at 0
5.13 shows
of water a
Mix 21
III‐M20/10‐SF
86
21. On the
mpared to
bility (4.8 x
). Partially
meability as
m2 which is
terials into
e concrete
easure the
asurement
d 24 hours.
or different
cient:
0 time (kg)
the results
absorption
Mix 23
III‐M20/10
Results a
depends
cementit
of water
hr0.5. Ho
0.32 kg/
concrete
mixes, t
OPC, mix
reductio
Figure 5
Figure 5
Increase in
mass per unit area (kg/m
2)
Water absorption coefficien
t (kg/m
2 hr0
.5)
and discussio
s on w/b ra
toius mater
r. Mix 21 m
wever, for m
/m2 hr0.5. It i
e mixes with
he absorptio
x 19 with re
n of absorpti
5.12: The inc
5.13: Absorp
0
0.5
1
1.5
2
0
Increase in
mass per unit area (kg/m
)
0
0.1
0.2
0.3
0.4
0.5
Mix 1
III
on of the op
atio, age, c
ials compos
ade with w/
mix 18 with w
s about 4 fo
h slag cemen
on coefficie
placing part
ion coefficien
crease in co
ption coeffic
1
Mix 1 (IIMix 5 (IIMix 9 (IIMix 19 (IMix 23 (I
1 Mix 2
III‐FA
ptimized con
uring, comp
ition and pr
/b ratio of 0
w/b ratio of
olds higher t
nt have lowe
nt ranges b
of cement w
nt to 0.1 kg/m
oncrete mas
cient of conc
1
Square ro
II)II-M20/10)II-M20/10-SF)I-M20/10-SF)III-M20/10)
Mix 5
III‐M20/10
ncrete prope
paction and
roperties hav
0.27 has the
f 0.42 and w
than that of
er absorptio
between 0.1
with 25 % of
m2 hr0.5.
ss with time
crete at age
2
oot of time (ho
Mix 2 Mix 7 Mix 1Mix 2
Mix 7 M
III‐SF III‐M2
erties
d aggregate
ve also an im
e lowest abs
with OPC, the
mix 21. It is
on than that
to 0.2 kg/m
f fine fly ash
e due to cap
e of 91 days
3
ours)
(III-FA)(III-SF)8 (I)1 (III-M20/10)
Mix 9 Mix
20/10‐SF I
properties
mportant eff
sorption coe
e water abso
s obvious fro
of mix 18 w
m2 hr0.5. Com
h and 10 %
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18 Mix 19
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[Hilsdorf, 1
fect on the a
efficient of 0
orption coeff
om the resu
with OPC. Fo
mpared to m
silica fume e
on
Mix 21
SF III‐M20/10‐S
87
1995]. The
absorption
0.08 kg/m2
ficient was
ults that all
or all these
mix 18 with
exhibited a
5
Mix 23
III‐M20/10F
Results a
5.4.3 C
Diffusion
Differen
investiga
2012]. T
Figure 5
chloride
chloride
m2/sec,
OPC wit
alone, it
ash exhi
alone (6
m2/sec).
is twice
chloride
(mixes 5
With w/
reductio
which ha
Figure 5
0
5
10
15
20
25
30
35
40
45
50
Chloride pen
etration dep
th (mm)
and discussio
Chloride di
n takes place
t methods
ation the m
This test me
5.15 and Fig
diffusion c
diffusion th
whereas for
th silica fum
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However, m
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as chloride d
5.14: Chlorid
0
5
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at 91 days
ix 9 Mix 1
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e result of co
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8 x 10‐13 m2/
tion of fine f
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Mix 21
III‐M20/10‐SFF
88
n gradient.
te. In this
lied [BAW,
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depth and
sistance to
f 9.2 x 10‐13
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with OPC
with fine fly
silica fume
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Mix 23
III‐M20/10F
Results a
Figure 5
5.5 D
5.5.1 M
Mechan
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the mech
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The add
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1
1
2
2
3
3
4
Chloride diffusion coefficient x 10
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and discussio
5.15: Chlorid
iscussion
Mechanica
ical propert
ur of concre
o predict th
r in this st
cy of concre
h have been
ssive strengt
t 312 kg/m3
asured mod
nal concrete
ge of about
es of the op
packing den
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te content r
ical propertie
dition of su
es from sev
ch tightens
0
5
10
15
20
25
30
35
40
Mix 1
III
on of the op
de diffusion
al propertie
ies are the
ete element
he performa
tudy, becau
te members
n studied. B
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. At the sam
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Mix 2
III‐FA
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By having a
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me time, the
icity are hig
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ture compa
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Firstly, the p
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Mix 5
III‐M20/10
ncrete prope
of concrete
tors that giv
ferent loads
ncrete when
mportance
rength and
close look
than 60 MPa
e tensile stre
gher than 4
the compres
respectively.
red to conve
keleton due
he volume fr
and bleedin
s has an im
pozzolanic re
aggregate‐
Mix 7 M
III‐M2III‐SF
erties
at 91 days
ve a good p
s. Usually co
n subjected
of determi
modulus of
to the resu
a at 91 days
ength of all
40 GPa for a
ssive strengt
. This signifi
entional con
e to applying
raction of co
g, which ha
mportant in
eaction turn
paste interf
Mix 9 Mix 1
20/10‐SF I
ossibility to
ompressive s
to differen
ning the th
elasticity al
ults, it can
s with total c
mixes range
all concrete
th and modu
icant enhan
ncrete can be
g the Ideal F
ncrete comp
as positive in
fluence on
ns CH into a
face, and t
18 Mix 19
I‐M20/10‐S
predict the
strength is c
nt loading c
hermal and
ong with co
be observed
cementitious
es between
e mixes. How
ulus of elast
cement in m
e attributed
uller curve.
ponents. The
nfluences on
concrete m
new pozzol
therefore m
Mix 21
III‐M20/10‐SFF
89
e structural
considered
conditions.
structural
ompressive
d that the
s materials
3 ‐ 6 MPa.
wever, for
ticity are in
mechanical
directly to
As known,
e increased
n concrete
mechanical
lanic C‐S‐H
modulus of
Mix 23
F III‐M20/10
Results and discussion of the optimized concrete properties 90
elasticity and late strength are markedly improved. Secondly, it enhances the packing density which
results in better compactness, thus the strength also increases [Peng, 2009]. Thirdly, fly ash addition
reduces the water demand which contribute to enhance the strength development. In addition, it
enhances the concrete microstructure through reducing the distances between the particles, which
leads to improving the mechanical properties of concrete. Moreover, the reduction of CH content
due to pozzolanic reaction makes the transition zone denser and stronger. Thus, the mechanical
properties, especially, elastic modulus are significantly improved. These effects are more noticeable
with using fine fly ash and silica fume. Fine fly ash is more reactive than normal fly ash, therefore,
mechanical properties are more enhanced [Maibaum, 2004; Chindaprasirt, 2005; Bentz, 2011].
Furthermore, the addition of fine materials reduces the micro bleeding and prevents the formation
of coarse pores in the transition zone and as a result the mechanical properties are significantly
improved [Erdem, 2012]. On the other hand, the strength of concrete is controlled by the strength
of the weakest zone, the interface between cement paste and aggregate [Popovics, 2011]. So,
strengthening the transition zone by adding fine materials leads to considerable increase in
mechanical properties. The results of modulus of elasticity, compressive strength and tensile
strength confirm the aforementioned explanation. The mechanical properties of mixes made with
fine materials (silica fume, fine fly ash or both) are superior to those with cement only or cement
with coarse fly ash. Because of its bigger size, the pozzolanic reaction of coarse fly is very slow which
reduces the strength development rate. On the other hand, the use of a low water content along
with the addition of fine particles prevent the internal bleeding beneath the aggregate particles that
after drying make the ITZ weaker and locus of micro‐cracks. As a result, the ITZ and microstructure
become denser and stronger which engender better mechanical properties. The compressive
strength of mix 21 reached 99 MPa while the modulus of elasticity was more than 50 GPa. This
enhancement in mechanical properties can be attributed directly to high density of the system.
In fact, it should be pointed out here that at different w/b ratio the behaviour of fine materials is
somewhat different. At w/b ratio of 0.42, the comparison of mix 5 and 9 showed that compressive
strength, tensile strength and modulus of elasticity of mix 5 with fine fly ash only was a little bit
higher than that of mix 9 with both fine fly ash and silica fume. While, at low w/b ratio (0.27), the
situation is totally reversed, the addition of both silica fume and fine fly ash enhanced the
mechanical properties more than the case of fine fly ash alone (mixes 21 and 23). The reason for
that may be the inefficient dispersion of silica fume in the first case because of the high content of
fine materials compared to the added superplasticizer dosage. However, in the other case (mix
21), higher dosage of superplasticizer was added which probably ensured better dispersion of fine
materials in the system. Therefore, the mechanical properties were significantly improved at the
same w/b ratio level. On the other hand, although the cement content is low, 312 kg/m3, (can be
Results and discussion of the optimized concrete properties 91
said lean mixes), the mechanical properties of mixes with fine fly ash are as high as that of high
strength concrete which need more cement, more silica fume and more superplasticizer content
per cubic meter. This can be reasoned by the higher packing density of the system, because the
strength depends fundamentally on the porosity and pore size distribution. The voids between
each particle classes are filled with the particles from the smallest class. Especially at the micro
scale, the gap between cement particles with average diameter of about 30 µm and the silica
fume with average diameter of 0.5 µm are filled with fine fly ash with diameter in the range of 1‐
10 µm, thus the packing density is notably enhanced. The improved packing density increases the
strength indirectly via improvement of workability, cohesion and compaction at fresh state as well
as reduction of porosity and increase of the matrix density at the hardened state. Furthermore,
the high filling ability of fine fly ash spheres enhances the transition zone strength which is the
locus of weakness and micro‐cracks. As a consequence, the bond between aggregate and cement
paste increases which results in the considerable improvement of mechanical properties as the
experimental results revealed.
5.5.2 Porosity
Pore structure of concrete has been studied for a long time as it strongly affects the concrete
durability and strength. Because of its major influence on concrete properties, three different
methods have been used to measure the porosity using different media: helium gas, mercury and
water. The results of the measured porosities with different methods were in the same trend. Indeed,
it should be pointed out here that the porosity measured with MIP was a little bit lower than the
porosities yielded via the other two methods. This is perhaps due to the pores shape and geometry,
which prevent the mercury molecules to penetrate and reach all voids, known as bottle neck
phenomena [Diamond, 2000]. Furthermore, the porosity measured using water is normally higher
because of the drying process during the specimens’ preparation which in addition to evaporating the
water in the voids, probably some of the inter‐layer water of C‐S‐H can be also evaporated. In this
part, only the experimental results of concrete porosity measured with MIP will be discussed.
The experimental results of concrete porosity measured with MIP indicated that the maximum
porosity was 10 % for mix 18 with OPC and w/b ratio of 0.42 and without supplementary materials,
which is comparable to conventional concrete. In order to evaluate the experimental results of
porosity in this investigation, a small comparison with traditional, high performance and ultra‐high
performance concrete will be made. It is reported that the total porosity of normal concrete, HPC,
and UHPC are in the range of 15, 8.3 and 6 % by volume respectively. It is reported also that the
capillary porosity contents (0.03 – 10 µm) are 8.3, 5.2 and 1.5 % by volume respectively [Teichmann,
Results and discussion of the optimized concrete properties 92
2004]. Results of mix 18 which can be considered as an optimized normal concrete showed that the
total and capillary porosities were 10 % and 5.6 % respectively, which are comparable to normal
concrete. These results significantly manifest the influence of enhancing the packing density on
concrete porosity. On the other hand, by maximizing the packing density of aggregate, the volume
of cement paste (cementitious materials and water) required to fill the voids between the aggregate
is reduced to about 23 %. However, for traditional concrete it is larger than about 30 %. So, if both
cement pastes have the same porosity, then the total porosity of the densely packed concrete will
be lower by about 25 %.
The use of supplementary materials appeared to reduce the porosity of concrete depending on their
type and content at w/b ratio of 0.42. The use of blended cement (slag cement), with higher fineness
than OPC, reduces the total and capillary porosities to about 9 % and 4.5 % respectively. More
reduction of porosities was attained by the addition of normal fly ash. The total and capillary porosities
of mix 2 with normal fly ash were reduced to about 7.8 and 3.9 % respectively. Similarly, mix 5 with
fine fly ash showed lower porosity; about 7 and 3.5 % for total and capillary porosities respectively,
which are comparable to the aforementioned porosities of HPC according to [Teichmann, 2004]. This
can probably be attributed to the efficient packing of fine fly ash particles which have small size (< 10
µm), spherical shape and smooth texture [Sinsiri, 2010]. The addition of silica fume to slag cement
reduces the porosity but not by the same way of fine fly ash. This may be due to the inefficient
dispersion and the possibility of agglomeration of the very fine particles of silica fume. On the other
hand, mix 19 made with OPC, fine fly ash and silica fume exhibited about 6.3 and 4.5 % for total and
capillary porosities respectively which are much lower than mix 18 without pozzolanic materials. At
low w/b ratio, the situation is clear and the porosity is significantly reduced. For mix 23 with w/b ratio
of 0.27 and with fine fly ash, the total and capillary porosities were 4.9 and 2.9 % respectively. More
reduction was gained at the same w/b ratio by the addition of silica fume to the system. Mix 21
exhibited around 1.9 % capillary porosity and about 3 % total porosity. These values are in the range of
UHPC which need more fines, cement, silica fume and fillers and more superplasticizer and special
mixing tools. The comparison of the measured porosity of mixes 21 and 23 with mixes 9 and 5
respectively emphasis the aforementioned assumption, that silica fume is more efficient in systems
with low w/b ratios than those with high w/b ratio.
To explain the previous results of total and capillary porosity of different mixes, it is basically worth
to repeat that all of these mixes prepared roughly with similar volume fractions of aggregate and
cementitious materials. The concrete mixture can be considered as a unit volume model that has to
be filled with the maximum well graded solid materials and at the same time to keep the produced
concrete as workable as possible. So, the aggregate content and grading has been optimised
Results and discussion of the optimized concrete properties 93
according to Ideal Fuller curve which exhibited the lowest voids content. These voids should be also
filled with dense cement paste. In addition to the cement paste, the transition zone between
cement paste and aggregate should be also as dense as possible. Cement particles with sizes of
about 30 µm cannot achieve this target alone. Therefore, another material with smaller size which
can fit in the voids between cement particles should be implemented. Fine fly ash is the ideal in
these conditions because it has a smaller size, a spherical shape, a smooth texture and pozzolanic
reactivity [Droll, 2004]. Going deeper, similarly, the voids between fine fly ash should be filled with
smaller size particles. Silica fume with average particle size of about 0.1 ‐ 0.5 µm could be the best
material that can fill the voids between fine fly ash. For more optimization, two main problems face
this model; the first one is how the efficient dispersion of these fine materials can be ensured. The
second one is how much the optimum content of each material is required to achieve the highest
packing density, taking into account all parameters such as the water demand, inter‐particle forces,
etc…
The role of fine fly ash in reducing the porosity and enhancing the pore size distribution can be
interpreted basically from several aspects. Firstly, the enhancement of the packing density as
mentioned above, which is responsible for reducing the porosity of the mixture [Droll, 2004].
Secondly, fine fly ash enhances the packing density at the aggregate surfaces, or by other words,
reduces the transition zone thickness. Thirdly, it reacts with CH in the transition zone, therefore, the
transition zone become denser and the pores become finer [Chindaprasirt, 2005]. Fourthly, the
pozzolanic reaction with CH produces pozzolanic C‐S‐H which granted more gel for densifying and
strengthening the matrix and the transition zone. Compared to normal C‐S‐H gel from OPC
hydration, pozzolanic C‐S‐H has lower porosity; the porosity of C‐S‐H gel is about 28 %, whereas
pozzolanic one has about 19 % [Bentz, 2000]. Additionally, the pozzolanic reaction takes place within
the capillary pores, and the hydration products blocks and reduces the size of capillary pores and
prevents its connectivity. Furthermore, the pozzolanic reaction takes some water of the free water
that is found in the system, which indirectly helps to reduce the porosity. Fifthly, it enhances the
cohesion of fresh concrete and reduces the amount of bleed water beneath the aggregate, and as a
result the transition zone becomes denser. Sixthly, because of its spherical shape and smooth
texture, it reduces the water demand and makes the microstructure more homogenous and denser.
Finally, because of its low hydration rate compared to cement, the hydration heat is low which
result in smaller thermal stresses at early ages. On the other hand, the only difference between fine
and normal fly ash is the particle size. Because of its relatively big size (most particles > 10 µm),
normal fly ash cannot fit between cement particles with the same particle size [Droll, 2004] which
results in poor packing density in the size level of 10 µm. Moreover, the transition zone is more
porous and the pores are coarser in the case of normal fly ash compared to fine fly ash. However the
Results and discussion of the optimized concrete properties 94
use of silica fume alone with cement (binary system) result in low packing density also because of
the high inter‐particle forces and the possibility of agglomeration. Silica fume should be uniformly
and homogeneously dispersed in order to achieve its pozzolanic and filler effects [Marchuk, 2004].
Agglomeration of the particles occurs with very fine substances which provoke poor packing density.
Therefore, the use of adequate cementitious materials with optimum composition, with the use of
appropriate superplasticizer that is sufficient to efficiently disperse the fine particles will lead to concrete
with dense microstructure and with very low porosity.
5.5.3 Durability
Durability is of major concern in the nowadays concrete mix design. Practically, the interest has
gradually shifted from the compressive strength towards other properties of the materials, such as
high modulus of elasticity, high density and durability. Concrete durability cannot be measured with a
uniform value, but the resistance of concrete to the ingress of water and gases is always of the most
crucial aspects. According to ACI committee [Virgalitte], durability of concrete is defined as its ability
to resist weathering action, chemical attack, abrasion or any other process of deterioration. The
transport of liquids and gases, which can be harmful to any concrete structure, occur exclusively through
the capillary pore system of the hardened cement matrix. In this investigation in order to assess the
durability of concrete; permeability, diffusion, and capillary suction tests have been implemented.
The transport of liquids and gases take place through the continuous pore system inside concrete.
So, enhancing the packing density reduces the penetration of contaminates into concrete. The
increased volume of aggregate close the transport passes and makes it longer. The experimental
results of penetration and air permeability tests clarify the important role of the increased packing
density on transport mechanisms. All concrete mixes exhibited water penetration depth lower than
20 mm which can be classified as impermeable concrete under aggressive conditions (< 30 mm)
according to Neville [Neville, 2004]. Because of its higher fineness, the use of slag cement reduces
the permeability more than OPC concrete. This result agrees with [Virgalitte, 1995; Güneyisi, 2008].
This is attributed to the dense microstructure and the lower content of CH crystals in the transition
zone in the case of slag cement concrete.
The addition of fine fly ash and silica fume notably reduces the concrete permeability and diffusivity
[Thomas, 2012]. The main effect of these fine materials is the enhancement of transition zone
properties and making it denser. This zone is known as the locus of micro‐cracks which influence not
only the mechanical properties but also the permeability and durability [Mehta, 2004]. Due to its
high pozzolanity, fine fly ash and silica fume increase the homogeneity of the microstructure by
replacing CH crystals with excess of C‐S‐H gel. Therefore, the probability of micro‐cracking is reduced
and the transition zone becomes thinner. Moreover, the size and content of capillary pores, which
Results and discussion of the optimized concrete properties 95
are responsible for transport as well as the CH‐crystal concentration, are reduced with progress of
the pozzolanic reaction. Furthermore, the produced C‐S‐H gel blocked the pores and reduced its size
and interrupted its connectivity. On the other hand, due to the high fineness and small particle size,
fine materials fill the space between cement particles and therefore refine the microstructure and
densify the matrix (filler effect). In addition, it reduces the wall effect around the aggregate surfaces,
thus allowing better packing of cement particles at the interface between cement paste and
aggregate. This filler effect makes the pores finer. The influence is clear with using different classes
of fine materials. The filler effect is greater the wider the differences between fine materials and
cement [Reschke, 2000]. These factors together lead to very positive influences on concrete
properties, particularly result in significant reduction in the permeability and considerable
enhancement in durability of concrete.
The incorporation of fine fly ash or both fine fly ash and silica fume with low w/b ratio result in an
effective reduction in the transport of contaminants into concrete. The results of absorption and
chloride diffusion confirm this influence. The water absorption coefficient of mix 23 was about 0.09
kg/m2 h0.5. However, a combination of fine fly ash and silica fume along with low water content
leaded to a much lower water absorption coefficient, which equals 0.07 kg/m2 h0.5. Similar results
were obtained for chloride penetration. The chloride penetration into concrete is considered to be
the most important factor that can be used to evaluate the concrete durability. The chloride
penetration of concrete without fine materials was about 42 mm. However, the use of blended
cement reduced the penetration to around 15 mm (mix 1). The use of fine fly ash at the same w/b
ratio of 0.42 reduced the penetration to about 7 mm. Mix 21 with w/b ratio of 0.27 showed the
lowest chloride penetration (about 3 mm) which is in the range of UHPC [Teichmann, 2004]. The
experimental results of mixes 5, 9, 21 and 23 confirm that silica fume is more effective in reducing
the transport of gases and fluids into concrete at low w/b ratio more than at high w/b ratio. Similar
conclusion has been emphasized by Bentz who reported that silica fume is more efficient for
reducing diffusivity in low w/c ratio concretes [Bentz, 2000]. The high resistance of concrete to
chloride penetration can be interpreted by several reasons; high packing density, optimization of
cementitious materials and low w/b ratio. The role of high packing density in reducing the chloride
diffusion coefficient can be clarified by comparing the experimental results from this investigation
with the results reported by Brandenburger [Brandenburger, 2006]. He studied the effect of fine fly
ash on chloride diffusion of concrete and found that fine fly ash concrete exhibited a chloride
diffusion coefficient of 1.5 x 10‐12 m2/sec. However the optimized mixes in this investigation showed
higher resistance to chloride diffusion than these values by using the same materials. For example,
the chloride diffusion of mix 5 made with the same w/b ratio and with the same fine fly ash content
is 3.8 x 10‐13 m2/sec which is 4 times lower than Brandenburger concrete with fine fly ash. This small
Results and discussion of the optimized concrete properties 96
comparison accurately elucidated the important effect of packing density on concrete durability. On
the other hand, the high resistance of concrete with supplementary materials to chloride ingress is
attributed to many parameters as discussed in the above sections. In addition to the
aforementioned parameters, the C/S ratio of the produced pozzolanic C‐S‐H has an important role.
The C‐S‐H from the pozzolanic reaction has a C/S ratio of about 1 which is much lower than that of
C‐S‐H gel from OPC hydration. It is stated that the lower the C/S ratio, the lower the chloride binding
[Droll, 2004]. It was found also that C‐S‐H with low C/S ratio has lower porosity than C‐S‐H with high
C/S ratio [Bentz, 2000]. Therefore, the pozzolanic C‐S‐H has important role in improving the
durability and reducing the porosity of concrete.
5.6 Porosity & mechanical properties relationship
In order to understand the interdependence between the measured properties of concrete in the
present investigation, the relationships between different properties have been studied. In general
the strength of most materials is increased when decreasing the porosity. An optimum addition of
fine materials helps to reduce the porosity and to improve the mechanical properties at the same
time. However, too much addition of fine materials increases the shrinkage which causes micro‐
cracking. The microstructure which is the main factor controlling the mechanical and chemical
properties depends mainly on the particle size distribution of the starting raw materials [Lange,
1997]. In addition, the properties of interface zone, porosity and micro‐cracking fundamentally
affect the mechanical properties. Figure 5.16 illustrates the mechanical properties and total porosity
relationship. It is clear that the relationship between porosity and mechanical properties is positively
correlated to a certain extent. Contrary to durability, all pores (open and close pores) affect the
mechanical properties of concrete [Beaudoin, 1979]. Strictly speaking, mechanical properties of
concrete are affected by the volume of all voids in concrete: entrapped air, capillary pores, gel
pores, and entrained air if present. Generally, from fracture mechanics point of view, at a given
porosity, smaller pores lead to a higher strength of the cement paste. Additionally, decreasing the
porosity and making the microstructure denser and more homogeneous results in beneficial effects
with respect to strength, resistance to crack propagation and stiffness. Besides, reducing the
porosity especially in transition zone makes the transition zone denser and enhances the bond
between cement paste and aggregate which has a direct influence on concrete elasticity and
strength. The concentration of CH crystals, which is a very weak material that weakens the
concrete, is reduced by minimizing the porosity in the TZ, thus mechanical properties of concrete
is more enhanced.
Results and discussion of the optimized concrete properties 97
Figure 5.16: Relationship between total porosity and modulus of elasticity and compressive
strength of different concrete mixes at age of 91 days
5.7 Permeability & capillary porosity relationship
The entrance of aggressive substances into concrete takes place via the pore system within concrete
microstructure and transition zone. The porosity of any material can be divided into two categories;
close and open. The open porosity can be also subdivided to two classes. The first type is the pores
that start from the surface and reach to the interior of the body and then stop. These pores do not
participate in transport properties. The second type is continuous pores from one side to the other
side permitting the passage of liquids and gases [Därr, 1973]. It is proved that the permeability of
concrete is well correlated to the average pore size and porosity measured with MIP [Hamami,
2012]. Figure 5.17 shows the relationship between the measured water penetration and air
permeability with capillary porosity. It is obvious from the figure that a clear relationship existed
between permeability and capillary porosity of concrete. The addition of fine pozzolanic material
which refine the pores and make it denser have a positive effect on permeability. On the other
hand, the experimental results showed that most concrete mixes have very low capillary porosity. It
is stated that at lower porosities (< 20 %), the capillary pores became discontinuous and the
transport is controlled by the properties of nano‐pores in C‐S‐H microstructure [Bentz, 2000].
10000
20000
30000
40000
50000
60000
2 4 6 8 10 12
Modulus of elasticity (MPa)
Total porosity %
0
20
40
60
80
100
120
2 4 6 8 10 12
Compressive stren
gth (MPa)
Total porosity %
Results and discussion of the optimized concrete properties 98
Figure 5.17: Relationship between capillary porosity measured with MIP in the range of 30 nm to
10 µm and the air permeability and water penetration depth at age of 91 days
5.8 Absorption & capillary porosity relationship
The absorption coefficient which represents the capillary suction effect has been determined using
the water absorption test. The dependence of absorption on capillary porosity is presented in
Figure 5.18. Certainly, as the capillary porosity increases, the capillary suction also increases.
Nevertheless, experimental results of both measurements do not exactly fit the line. This might be
due to the differences of the measuring media; water and mercury. Additionally, beside the size, the
shape and geometry of the pores play important roles in determining the transport of fluids and
gases through concrete. Furthermore, the measuring period of the water absorption affects the
results because it is continued for 24 hours.
Figure 5.18: Water absorption coefficient and capillary porosity relationship at age of 91 days
0
2
4
6
8
10
12
14
16
1 2 3 4 5 6
Air permeability 10‐17 (m
2)
Capillary porosity %
0
5
10
15
20
25
1 2 3 4 5 6
Water pen
etration depth (mm)
Capillary porosity %
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
1 2 3 4 5 6
Water absorption coefficient
(kg/m
2hr0
.5)
Capillary porosity %
Results and discussion of the optimized concrete properties 99
5.9 Chloride diffusion & capillary porosity relationship.
Chloride ions diffusion is most effective when the pores are totally saturated, but it occurs also in
partially saturated ones [Neville, 2004]. Figure 5.19 presents the relationship between chloride
diffusion coefficient and the capillary porosity. It is clear that the relationship between capillary
porosity and chloride diffusion is positively correlated; as the capillary porosity increases the
diffusion coefficient increases. Similar relationship between capillary porosity and diffusion has been
documented by Bentz [Bentz, 2000]. On the other hand, the addition of fine pozzolanic materials
modifies the pore structure of the cement paste. The pozzolanic reaction takes place within the
capillary pores and the products may fill and block some of these pores and make them
discontinuous. Such pore modification and blocking are more pronounced in the case of very fine
materials. As a result of this refinement, the chloride penetration is considerably reduced.
Figure 5.19: Chloride diffusion coefficient & capillary porosity relationship at 91 days
0
1
2
3
4
5
6
7
8
9
10
1 2 3 4 5 6
Chloride diffusion coefficien
t x 10‐13 (m
2/sec)
Capillary porosity %
Results and discussion of the optimized concrete properties 100
Effect of hydrothermal conditions on the properties of densely packed concrete 101
6. Effect of hydrothermal conditions on the properties of
densely packed concrete
6.1 Introduction Although the behavior of normal concrete at high temperature and fire is intensively studied in the
literature, there is a lack of information about the influence of elevated temperature on the
properties of high performance concrete containing mineral admixtures. Most investigations
concentrated only on the residual mechanical properties and a little information is available on
concrete durability which controls the service life of different structures. In addition, the available
information about the effect of hydrothermal treatment on properties of already cured concrete is
very rare. When the concrete is subjected to elevated temperature, changes in durability and
strength take place [Xu, 2001]. However, the mechanism causing these changes is complex as a
result of large number of physical and chemical processes in concrete microstructure. The literature
review about the behavior of concrete at high temperature give widely varying results which make it
difficult to draw definite conclusions. For example, the residual strength after exposing to 200 °C
could vary from a decrease of 50 per cent to an increase of 50 percent [Bažant, 1996]. The reasons
for that include the differences in moisture content, in exposing time, in concrete composition, and
in aggregate properties [Neville, 2004].
As one of the main targets of this investigation is to develop hot water tank to store solar thermal
energy at 200 °C and pressure of 15.5 bars, then the optimized concrete should be tested under
these hydrothermal conditions. Two aspects should be considered in this concern; the first is the
structural design including thermal stresses, geometry of the tanks and walls as well as the
structural behavior of concrete under hydrothermal cyclic loads (fatigue). The second aspect is the
behavior of concrete itself under hydrothermal conditions which is the main focus of this
investigation. The used concrete should be water‐tight at high temperature, durable and sustainable
for long working period. The principal goal of this chapter is to evaluate the effect of hydrothermal
conditions on properties of the densely packed concrete. Contrary to the case of the pure heat
exposure, where the concrete specimens are subjected to pressure gradient which may lead to
spalling, in the case of hydrothermal exposure (temperature and pressure), the pressure gradient is
not so aggressive like the first case. Additionally, in the case of heat only, the concrete suffers
dryness because it loses its pore water due to heating [Bažant and and Prasannan, 1986], whereas,
in the studied case (hydrothermal exposure), the pores are completely saturated with water. In this
investigation, in order to study the properties and microstructure of the optimized HPC under
different thermal conditions, a series of experimental tests have been performed.
Effect of hydrothermal conditions on the properties of densely packed concrete 102
This chapter presents the experimental results of the optimized concrete mixes after hydrothermal
exposure to a temperature of 200 °C and a pressure of 15.5 bars for several cycles up to 50.
Mechanical properties including compressive, tensile strength and hardness of concrete using
rebound number are introduced. Furthermore, porosity measurements using MIP will be also given.
In addition, the durability indicators including measurement of different transport phenomena;
diffusion, permeation and capillary suction are presented. At the end of this chapter, detailed
analysis and discussions of the experimental results are included.
6.2 Methods
In real situation of the hot water concrete tank, because the tank is totally closed, increasing the
temperature above 100 °C will generate water and steam pressure on the concrete walls. So, the
concrete will subject to temperature and pressure from one side while the other side is kept at
ambient conditions. However, due to the lack of information about the behaviour of the developed
densely packed concrete under hydrothermal conditions, it is favoured to study first the properties
of concrete after hydrothermal exposure from all sides. Therefore, in this experimental work, the
autoclave has been used to load the concrete specimens with temperature of 200 °C and pressure of
15.5 bars as seen in Figure 6.1. The height of the autoclave is about 1120 mm and the outer
diameter is about 550 mm with a pressure vessel from inside with volume of approximately 7.8
liters. The autoclave contains two heating units; bigger and smaller with capacity of 1600 and 400
watt respectively. A pressure gauge that enables setting the desired pressure value and pressure
valve are located on the enclosure. Additionally, a cooling fan is included in order to cool down the
pressure vessel if required. The pressure vessel has a diameter of about 170 mm and height of about
350 mm which makes it approximately suitable for 1 standard cylinder (300 x 150 mm) as a
maximum. The hydrothermal loading was applied for several autoclaving cycles, each one needs of 3
hours heating at a constant heating rate of 1 °C/min, and 6 hours cooling at constant rate of 0.5
°C/min for cooling down to the room temperature (20 ± 1 °C) as can be seen in Figure 6.1. Because
of the limited size of the used autoclave, either three cubes with edge length of 100 mm of each mix
or one cylinder (150 x 300 mm) were subjected to several hydrothermal cycles; 5, 10, 15 or 50 times.
Thereafter, the specimens were cooled down to ambient conditions and then tested at normal
temperature to study the variation in their properties due to autoclaving.
Effect of
Figure 6
6.3 M
6.3.1 C
The com
the plan
different
of some
showed
(strength
reduced
decrease
of norm
to reduc
was abo
compare
compres
quite di
reduced
both fine
only, mi
resistanc
slag cem
bit decre
f hydrotherm
6.1: High pre
Mechanical
Compressi
mpressive str
nned curing
t autoclavin
concrete m
that OPC a
h retrogress
to 61 % of
e of strength
al fly ash ap
ce. Neverthe
out 136 % of
ed to other
ssive strengt
fferent perf
to approxim
e fly ash and
ix 19 with p
ce to strengt
ment, fine fly
ease of abo
mal conditio
essure auto
l propertie
ive strength
rength has b
period at 2
g cycles wit
ixes, while t
and slag ce
sion). The st
f the origina
h to about 7
ppeared to i
eless, the fin
f its original
r mixes. M
th was abou
formance. T
mately its or
d silica fume
partial repla
th retrogres
y ash and sili
out 2 % can
ns on the pr
oclave and a
es results
h
been measu
20 ± 1 °C u
h 200 °C an
the results o
ment concr
trength of O
al strength.
8 % of its or
ncrease the
nal compress
l value, whic
ix 5 with f
ut 130 % of
The strength
riginal value
e is about 1
acement of
ssion after ex
ica fume ma
be noticed
roperties of
a schematic
red for all m
under water
d 15.5 bars.
of other mixe
rete exhibite
OPC concret
Similarly, s
riginal value
e strength un
sive strengt
ch represen
fine fly ash
the origina
h is increas
after 50 cyc
26 % of its
OPC with f
xposure to 5
anifested an
due to incr
0
50
100
150
200
250
0Temperature °C
densely pac
c diagram fo
mixes using
r, the concr
. Figure 6.2
es can be fou
ed decrease
te (mix 18)
lag cement
due to auto
ntil 15 cycle
h of mix 2 w
ts the maxi
showed s
l strength. M
sed with au
cles. Howeve
original valu
fine fly ash
50 cycles. At
increase of
reasing the
5
ked concret
or hydrother
100 mm edg
rete specim
presents the
und in the a
e of strengt
after autoc
concrete (m
oclaving for 5
es, after whi
with normal
mum increa
imilar trend
Mix 7 with s
utoclaving fo
er, the final
ue. Compare
and silica f
t low w/b ra
strength wi
autoclaving
10
Time (hours)
e
mal loading
ge length cu
ens were e
e experimen
ppendices. T
th due to a
laving for 5
mix 1) also
50 cycles. Th
ch the stren
fly ash afte
ase due to a
d, however,
silica fume
or 5 cycles
strength of
ed to mix 18
fume exhibit
atio (0.27), m
ith autoclavi
g cycles from
0 1
103
g period
ubes. After
exposed to
ntal results
The results
autoclaving
0 cycles is
suffered a
he addition
ngth began
r 50 cycles
autoclaving
, the final
revealed a
then it is
mix 9 with
8 with OPC
ted higher
mix 21 with
ing. A little
m 15 to 50
15
Effect of hydrothermal conditions on the properties of densely packed concrete 104
cycles. Nevertheless, the final compressive strength is about 112 % of its original value (without
autoclaving). On the other hand, mix 23 with w/b ratio of 0.27, with slag cement and fine fly ash
showed a negligible strength retrogression at all levels of autoclaving. The final compressive
strength was about 117 MPa which represents about 129 % of its original value.
6.3.2 Rebound number
The aim of this test is to measure the effect of autoclaving with various cycles on the hardness and
strength of concrete, on the same cube. After the designed curing period, the samples were
surface dried and then tested to determine its hardness in the original state without autoclaving.
Then, the specimens were put in the autoclave for different cycles. After autoclaving, the concrete
specimens were surface dried and tested again. In order to apply the rebound number test, the
specimens were fixed in compressive strength machine under a certain load with a certain loading
rate as can be seen in Figure 3.11. All samples are tested by the same way in order to get fair
comparison of the results. The experimental results of rebound number test on concrete
specimens are presented in Figure 6.3. It is not difficult to observe that the results of rebound
number are in good agreement with the results of compressive strength. The strength decrease
can be observed significantly in mixes 1 and 18 with slag cement and OPC concrete respectively. It
is clear that w/b ratio has a major effect on strength of concrete before and after autoclaving.
Furthermore, the results indicated that the addition of pozzolanic materials considerably
enhances the strength of concrete after hydrothermal exposure for different cycles; depending on
its type and content. It can be also indicated that mixes with fly ash continuously gain strength
with increasing the autoclaving cycles. However, mixes with silica fume gained high strength
quickly and then the strength is constant or slowly increases with autoclaving. The results of mix
18 showed that the strength is aggressively decreases with autoclaving for 50 cycles which is
typically the case in the compressive strength test results.
Effect of hydrothermal conditions on the properties of densely packed concrete 105
Figure 6.2: Compressive strength of concrete mixes at normal conditions and after autoclaving.
40
50
60
70
0 10 20 30 40 50Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 18 (III)
50
60
70
80
90
100
110
0 10 20 30 40 50Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 2 (III‐FA)
50
60
70
80
90
100
0 10 20 30 40 50Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 5 (III‐M20/10)
50
60
70
80
90
100
0 10 20 30 40 50
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 7 (III‐SF)
50
60
70
80
90
100
0 10 20 30 40 50Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 9 (III‐M20/10‐SF)
40
50
60
70
80
90
0 10 20 30 40 50
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 18 (I)
60
70
80
90
100
110
0 10 20 30 40 50Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 19 (I‐M20/10‐SF)
80
90
100
110
120
0 10 20 30 40 50
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 21 (III‐M20/10‐SF)
80
90
100
110
120
0 10 20 30 40 50
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 23 (III‐M20/10)
Effect of hydrothermal conditions on the properties of densely packed concrete 106
Figure 6.3: Results of rebound hammer for concrete at normal conditions and after autoclaving
for several cycles
30
35
40
45
50
0 10 20 30 40 50
Rebound number
Number of autoclaving cycles
Mix 1 (III)
35
40
45
50
55
0 10 20 30 40 50
Rebound number
Number of autoclaving cycles
Mix 2 (III‐FA)
30
35
40
45
50
55
0 10 20 30 40 50
Rebound number
Number of autoclaving cycles
Mix 5 (III‐M20/10)
30
35
40
45
50
55
0 10 20 30 40 50
Rebound number
Number of autoclaving cycles
Mix 7 (III‐SF)
30
40
50
0 10 20 30 40 50
Rebound number
Number of autoclaving cycles
Mix 9 (III‐M20/10‐SF)
35
40
45
50
0 10 20 30 40 50
Rebound number
Number of autoclaving cycles
Mix 18 (I)
35
40
45
50
55
0 10 20 30 40 50
Rebound number
Number of autoclaving cycles
Mix 19 (I‐M20/10)
40
45
50
55
0 10 20 30 40 50
Rebound number
Number of autoclaving cycles
Mix 21 (III‐M20/10‐SF)
40
45
50
55
0 10 20 30 40 50
Rebound number
Number of autoclaving cycles
Mix 23 (III‐M20/10)
Effect of
6.3.3 S
Cylindric
the desig
the test
week. Th
autoclav
tested.
conditio
at w/b ra
mix 19 i
and 5 ex
hand, m
addition
with 10
autoclav
fine fly a
same lev
Figure 6
6.4 Po
The mai
concrete
in the c
0
1
2
3
4
5
6
7
Splitting tensile stren
gth (MPa)
f hydrotherm
Splitting ten
cal specimen
gned curing
was perfor
he autoclav
ving, the sam
Figure 6.4 p
ns and after
atio of 0.42,
n which the
xhibited a sl
mix 1 reveale
of silica fu
0 % silica f
ving. At low
ash and silic
vel without a
6.4: Splitting
orosity me
in target of
e samples af
concrete mi
Mix 1
Normal
15 cycle
III
mal conditio
nsile streng
ns with dime
g period. Bec
med after 1
ing process
mples were
presents the
r hydrotherm
, most concr
e tensile stre
light decrea
ed the highe
me has a n
ume replac
w/b ratio, a
ca fume. How
any changes
g tensile stre
easured w
this test is
fter hydroth
crostructure
Mix 2 M
es
III‐FA III‐
ns on the pr
gth
ensions of 1
cause of the
15 cycles of
was perfor
allowed to c
e results of
mal exposur
rete mixes s
ength increa
se in tensile
est strength
egligible eff
cement exh
a little bit de
wever, only
s due to auto
ength at nor
with MIP
s to determ
ermal expos
e due to au
Mix 5 Mi
‐M20/10 III‐
roperties of
150 x 300 m
e limited vol
autoclaving
med one we
cool down t
f splitting te
e for 15 cycl
uffer a decr
ased by abou
e strength; a
reduction d
fect on prev
ibited abou
ecrease of st
y mix 23 wit
oclaving.
rmal conditio
ine the por
sure which c
utoclaving. A
ix 7 Mix
‐SF III‐M20/1
densely pac
m were sub
ume of the
g only, wher
eek before
to the room
ensile streng
les at age of
ease in tens
ut 13 % com
about 7 and
due to autoc
venting the
ut 40 % re
trength can
h fine fly as
ons and afte
re size distr
can help to
After curing
9 Mix 18
10‐SF I
ked concret
bjected to au
autoclave (1
re each cylin
the test, at
temperatur
gth of conc
f 91 days. Th
sile strength
mpared to it
d 10 % respe
claving, whi
tensile stre
duction of
be observed
sh held the t
er autoclavi
ibution and
better unde
g, the samp
8 Mix 19
I‐M20/10‐SF
e
utoclaving c
17 x 35 cm,
nder needs
age of 83 d
re (20 ± 1°C
crete mixes
he results ind
. The only ex
s original va
ectively. On
ch is about
ngth reduct
the strengt
d for mix 21
tensile stren
ing for 15 cy
the total p
erstanding th
ples were e
Mix 21
III‐M20/10‐SF
107
cycles after
7.8 liters),
about one
days. After
C) and then
at normal
dicate that
xception is
alue. Mix 2
n the other
41 %. The
tion. Mix 7
th due to
1 with both
ngth at the
ycles
porosity of
he changes
exposed to
Mix 23
III‐M20/10
Effect of
autoclav
the test
Figure 6
hydrothe
increase
OPC wit
porosity
pozzolan
result of
5.34 % d
very sma
porosity
conditio
Figure 6
figure re
autoclav
reduced
with poz
50 cycle
remaine
for 50 cy
reduced
Figure 6
autoclav
f hydrotherm
ving for 50 cy
ing device.
6.5 illustrat
ermal expo
ed from 10.3
th fine fly a
is still high
nic materials
f mix 5. The
due to autoc
all reduction
with autoc
n was 4.9 %
6.6 shows th
evealed that
ving for 50 c
from 3.5 to
zzolans exhi
s. At low w
d approxim
ycles. On th
from 2.96 %
6.5: Total
ving for 50 c
0
2
4
6
8
10
12
14
16
Total porosity %
mal conditio
ycles. After
Detailed ex
tes the tot
sure for 50
3 to 13.3 %
sh and silic
her than th
s seemed to
porosity of
claving for 50
n in porosity
claving for 5
, and it was
he experime
t mix 18 exh
cycles, 5.6 %
o 1.74 % aft
bited a decr
w/b ratio, the
ately withou
e other han
% at normal
porosity of
cycles
Mix 5
III‐M20/10
ns on the pr
cooling dow
planation o
tal porosity
0 cycles. Th
after autoc
a fume (mix
he original o
o have bette
mix 5 made
0 cycles. At
y to 2.98 % a
50 cycles wa
reduced to
ental results
hibited the h
% and 9.26 %
er hydrothe
rease in the
e capillary p
ut change, 1
nd, the capil
conditions t
f concrete
Mix 18
I
roperties of
wn to room t
n the meas
of concre
he results in
laving for 50
x 19), the in
one (from 6
er performan
e with slag ce
low w/b rat
after autocla
as clear for
2.65 % after
s of capillar
highest capi
% respectiv
ermal treatm
capillary po
porosity of m
1.9 % at amb
lary porosity
to 1.44 % aft
measured
Mix 1
I‐M20/1
densely pac
temperature
uring proce
ete mixes a
ndicated th
0 cycles. Ho
ncrease in p
6.2 to 7.9 %
nce concern
ement and f
io, mix 21 w
aving for 50
mix 23, wh
r hydrotherm
ry porosity
illary porosit
ely. Howeve
ment. Mix 19
orosity from
mix 21 with
bient condit
y of mix 23
ter hydrothe
with MIP
19 Mix
10‐SF III‐M20
ked concret
e, the sample
dures is fou
at normal
at the tota
owever, by p
porosity is r
%). The use
ing porosity
fine fly ash w
with bulk por
cycles. How
here the tot
mal treatme
of different
ty at norma
er, the capil
9 with partia
4.5 to 2.4 %
both fine f
tions and 1.8
with fine fly
ermal treatm
at normal
x 21 M
N
5
0/10‐SF III‐
e
es were tran
und in sectio
conditions
al porosity
partial repla
reduced, bu
of slag cem
y as can be s
was reduced
rosity of 3 %
wever, the re
tal porosity
nt for 50 cyc
t concrete m
al conditions
lary porosit
al replaceme
% after auto
fly ash and s
87 % after a
y ash was si
ment for 50 c
conditions
Mix 23
Normal
0 cycles
‐M20/10
108
nsferred to
on 3.4.4.3.
and after
of mix 18
acement of
ut the final
ment with
seen in the
d from 7 to
% showed a
eduction in
at normal
cles.
mixes. The
s and after
ty of mix 5
ent of OPC
oclaving for
silica fume
autoclaving
ignificantly
cycles.
and after
Effect of
Figure 6
6.5 D
When th
occur, pa
order to
conditio
properti
The mea
conditio
6.5.1 P
6.5.1.1
The wat
days. On
After au
were cut
applied f
device, t
measure
results o
autoclav
increase
value fo
f hydrotherm
6.6: Capillar
urability
he concrete
articularly d
o find out w
ns or not,
es of concre
asurements
ns and comp
Permeabili
Water pen
er penetrati
ne week bef
utoclaving, th
t and fixed i
for 72 ± 2 ho
they are sub
ed, the wett
of water pen
ving for 15
ed for all mix
r mix 1. It w
0
1
2
3
4
5
6
7
8
9
10
Capillary porosity %
mal conditio
ry porosity o
e is exposed
durability, wh
whether the
a series of
ete which giv
include pe
pare them w
ity
netration de
ion depth te
fore the test
he samples
n the testing
ours. Therea
bjected to sp
ted zone ap
netration de
cycles. The
xes, but cert
was increase
Mix 5
III‐M20/10
ns on the pr
of concrete a
d to hydrot
hich can red
ere was deg
f experimen
ve indicatio
rmeability,
with those at
epth.
est according
t, the cylind
were coole
g device as c
after, during
plitting by th
ppeared dar
pth of concr
test result
tainly not in
ed from 15 t
Mix 18
I
roperties of
at normal co
hermal con
duce the rem
gradation of
ntal tests h
ns about the
absorption
t normal con
g to DIN EN
rical sample
d down to t
can be seen
g 10 minutes
he machine.
rker [Neville
rete at norm
ts indicated
the same m
to 50 mm d
Mix 1
I‐M20/10
densely pac
onditions an
ditions, sign
maining serv
f the concre
has been pe
e durability
and diffusio
nditions.
12390‐8 ha
es were exp
the room te
in Figure 3.
s of removin
The depth
e, 2004]. Fig
mal condition
that the p
manner. It w
ue to autoc
19 Mi
0‐SF III‐M2
ked concret
nd after auto
nificant cha
vice life of th
ete durabilit
erformed. I
of concrete
on after exp
as been imp
osed to aut
emperature.
13. A pressu
ng the speci
of water pe
gure 6.7 sho
ns (without
penetration
as about thr
laving for 15
x 21
N
5
20/10‐SF
e
oclaving for
nges in its
he structure
ty after hyd
n this sect
have been
posure to a
lemented at
oclaving for
. Then, the
ure head of
mens from t
enetration w
ows the exp
autoclaving
depth is dr
ree folds of
5 cycles. Ho
Mix23
Normal
50 cycles
III‐M20/10
109
50 cycles
properties
rapidly. In
drothermal
tion, some
measured.
autoclaving
t age of 91
r 15 cycles.
specimens
5 bars was
the testing
was directly
perimental
) and after
ramatically
its original
owever, for
Effect of
mix 18 w
times its
imperme
several t
depths.
and 5 m
Figure 6
15 cycle
6.5.1.2
The co
section 3
diamete
20 mm.
thereaft
105 °C u
conditio
carried o
concrete
Contrary
imperme
permeab
0
10
20
30
40
50
60
70
80
90
Water pen
etration dep
th (mm)
f hydrotherm
with OPC o
s original v
eability of co
times of its o
Compared t
m to 24 and
6.7: Water p
es
Air perme
ncrete air
3.4.3.2. Afte
r of 50 mm
Then, the
er they were
until a consta
ns to avoid
out as expla
e in three dif
y to the res
eability of m
bility due to
Mix 1
III
mal conditio
nly, the pen
value (18 m
oncrete afte
original valu
to its origina
d 22 mm for
penetration
ability
permeabili
er curing for
were taken
samples we
e cooled dow
ant mass. Th
d any moist
ained in the
fferent case
ults of wate
most concre
o hydrotherm
Mix 2
III‐FA II
ns on the pr
netration de
m). The ad
er hydrother
ue. At low w
al values, th
mixes 21 an
depth of co
ity was m
r the planne
n. Afterward
ere exposed
wn to the ro
hen, the sam
ure uptake.
e section 3.4
s; normal, w
er penetratio
ete mixes w
mal cycling.
Mix 5 M
I‐M20/10 II
roperties of
epth reache
ddition of fl
mal exposur
w/b ratio, mix
he penetrati
nd 23 respec
oncrete at n
measured ac
ed period, w
s, the samp
to autoclav
oom temper
mples were
. Then, the
4.3.2. Figure
with autoclav
on depth, th
with autoclav
It has the s
Mix 7 Mix
II‐SF III‐M20/
densely pac
ed about 82
y ash show
re. Neverthe
xes 21 and 2
ion depth af
ctively.
normal cond
ccording to
with the help
les were cut
ving for the
rature. The s
cooled natu
measurem
e 6.8 shows
ving for 15 a
he results in
ving. Only m
ame trend a
x 9 Mix 18
/10‐SF I
ked concret
2 mm which
wed a quite
eless, the pe
23 showed q
fter autocla
ditions and a
o the proc
p of drilling m
t to slices w
e designed n
saturated dis
urally to 20 ±
ents and ca
the results
and with aut
ndicated en
mix 18 show
as that of w
8 Mix 19
I‐M20/10‐SF
e
h represents
improveme
enetration de
quite high p
ving increas
after autocl
cedure des
machine sam
with thicknes
number of
scs were ove
± 1 °C in mo
alculations h
of air perm
toclaving for
hancement
wed an incre
water penetr
Mix 21
F III‐M20/10‐SF
110
s around 5
ent in the
epth is still
enetration
sed from 3
aving with
scribed in
mples with
ss of about
cycles and
en dried at
oisture free
have been
meability of
r 50 cycles.
in the gas
ease in air
ration test.
Mix 23
Normal
15 cycles
III‐M20/10
Effect of
For othe
2 with fl
initial va
fine fly a
w/b ratio
permeab
1.4 and
Figure 6
15 and 5
6.5.2 A
In this i
Concrete
days). O
for 15 c
constant
Thereaft
to allow
increase
The abso
of concr
coefficie
increase
coefficie
0
5
10
15
20
25
Air permeability x 10‐17(m
2)
f hydrotherm
er mixes, larg
y ash, after
alue. On the
ash resulted
o, a significa
bility at norm
1.53 x 10‐17
6.8: Air perm
50 cycles
Absorption
nvestigation
e cubes wer
ne week be
ycles. After
t weight. T
ter, the circu
flow of wat
e with time o
orption coef
rete samples
nt of differe
d for most
nt before an
Mix 1
III
mal conditio
ge reduction
autoclaving
other hand
d in a reduct
ant decrease
mal conditio
m2 respectiv
meability co
n (Capillary
n, the capill
re cast, dem
fore the tes
cooling to
hen, the sa
umferences
ter in one d
of concrete m
fficient has b
s. Figure 6. 1
ent mixes aft
mixes with
nd after aut
Mix 2
IIIII‐FA
ns on the pr
n in permea
g for 50 cycle
d, replacing
tion in air p
e in air perm
ons exhibited
vely.
oefficient of
y suction)
ary suction
moulded and
st, some cub
room temp
amples wer
of the speci
irection only
mixes after a
been calculat
10 presents
ter hydrothe
h autoclavin
toclaving for
Mix 5 M
II‐M20/10 I
roperties of
bility can be
es, the air p
part of ordin
ermeability
meability can
d much redu
concrete at
has been d
cured unde
bes were cut
erature, the
re cooled d
mens were
y. Figure 6.9
autoclaving f
ted accordin
the effect o
ermal exposu
g. Mix 18 w
r 15 cycles, i
Mix 7 Mix
II‐SF III‐M20/
densely pac
e noticed. Th
permeability
nary Portlan
to 42 % of
n be observe
uction with a
t normal con
determined
er water at 2
t, polished a
e specimens
own natura
coated with
9 shows the
for 15 cycles
ng to equatio
of hydrother
ure. The res
with OPC s
it was increa
x 9 Mix 18
/10‐SF I
ked concret
he maximum
was reduce
nd cement w
its original v
ed. Mixes 21
autoclaving
nditions and
according t
21 °C until t
and then su
s were oven
ally at mois
transparen
experiment
s.
on 5.3 based
rmal treatm
ults indicate
howed the
ased by abo
8 Mix 19
I‐M20/10‐SF
e
m reduction
ed to about
with 10 % SF
value (mix 1
1 and 23 wit
for 50 cycle
d after autoc
to DIN EN I
the day of th
bjected to a
n dried at 10
sture free c
t paraffin wa
tal results o
d on the ma
ent on the
e that the ab
maximum
out 56 % of
Mix 21
N
1
5
III‐M20/10‐SFF
111
was in mix
27 % of its
F and 25 %
19). At low
th very low
es to about
claving for
SO 15148.
he test (91
autoclaving
05 °C until
conditions.
ax in order
f the mass
ss increase
absorption
bsorption is
absorption
its original
Mix 23
Normal
15 cycles
50 cycles
III‐M20/10F
Effect of
value. Th
in mix 1
plays a p
quite inc
cement a
15 cycles
with fine
Due to h
absorpti
Figure 6
Figure 6
for 15 cy
Increase in m
ass per unit area (Kg/m
2)
0.
0.
0.
0.
0.
0.
Absorption coefficien
t (kg/m
2hr‐0.5)
f hydrotherm
he use of ble
due to auto
positive role
crease in th
and pozzola
s resulted in
e fly ash is th
hydrotherma
on coefficien
6.9: Mass in
6. 10: Water
ycles
00.20.40.60.81
1.21.41.61.82
2.22.42.6
0
0
.1
.2
.3
.4
.5
.6
Mix 1
III
mal conditio
ended cemen
oclaving was
in determin
he absorptio
nic materials
an increase
he only mix s
al treatment
nt of about 9
crease of d
r absorption
1
Mix 1 (III)
Mix 5 (III‐M2
Mix 9 (III‐M2
Mix 19 (I‐M2
Mix 23 (III‐M
Mix 2
III‐FA
ns on the pr
nt reduced t
s 34 % of its
ning the cap
n coefficien
s (mixes 5, 7
e of absorpti
showing a de
t for 200 °C
92 % of its or
ifferent con
n coefficient
Squar
20/10)
20/10‐SF)
20/10‐SF)
M20/10)
Mix 5
III‐M20/10
roperties of
the increase
s original va
pillary suctio
t can be re
7 and 9). At l
on coefficien
ecrease in its
and pressur
riginal value.
crete mixes
t of concrete
2re root of time
Mix 2 (III
Mix 7 (III
Mix 18 (I
Mix 21 (I
Mix 7 M
III‐SF III‐M2
densely pac
in absorptio
lue. Howeve
n of concret
ecognized fo
low w/b rati
nt by about
s absorption
re of 15.5 ba
.
s after autoc
e at normal
3e in hours
‐FA)
‐SF)
)
II‐M20/10‐SF)
Mix 9 Mix
20/10‐SF I
ked concret
on due to aut
er, the use o
te after hyd
or mixes wit
o, the hydro
7 % for mix
coefficient t
ars for 15 cy
claving for 1
conditions
4
18 Mix 19
I‐M20/10‐S
e
toclaving. Th
of pozzolanic
rothermal e
h combinati
othermal tre
21. In contr
than the orig
ycles, mix 23
5 cycles
and after a
9 Mix 21
SF III‐M20/10‐S
112
he increase
c materials
xposure. A
ion of slag
atment for
ast, mix 23
ginal value.
3 exhibited
utoclaving
5
Mix 23
Normal
15 cycles
III‐M20/10SF
Effect of
6.5.3 C
The chlo
section 3
from the
cycles. A
been im
experim
hydrothe
maximu
penetrat
is higher
increase
Howeve
penetrat
Furtherm
exposure
cycles (a
current,
concrete
conditio
mix 18 is
m2/s aft
than tha
Figure 6
for 50 cy
f hydrotherm
Chloride di
oride diffus
3.4.3.4. Cyli
e core of sta
After natural
mplemented
ental result
ermal expos
m penetrat
ted water re
r than the p
e in diffusion
r, for mixes
tion depth
more, mix 2
e. The pene
about 7 mm
the chloride
e mixes. Fig
ns and after
s higher tha
er autoclavi
at of mix 18 a
6.11: Chlori
ycles
0
10
20
30
40
50
60
Chloride pen
etration depth
(mm)
mal conditio
iffusion
ion of conc
ndrical spec
andard concr
lly cooled do
to measure
ts of chlor
sure. The r
ion depth (
eached the o
presented va
n due to au
s with low w
of mix 21
3 exhibited
etration dep
m). From the
e diffusion c
gure 6.12 p
r autoclavin
an 3.7 x 10‐1
ing for 50 cy
after autocla
de penetrat
Mix 5
III‐M20/10
ns on the pr
crete has be
cimens with
rete cylinde
own to the
e the chlorid
ride penetra
esults revea
(> 50 mm).
other side o
alue. On the
utoclaving fo
w/b ratio, h
increased
a good resi
pth remained
e knowledg
coefficient ca
presents th
g for 50 cyc2 m2/s. How
ycles. That m
aving with 5
tion depth o
Mix 18I
roperties of
een measur
diameter o
rs. Then, the
room tempe
de penetrati
ation depth
aled that af
Hence the
f the sample
e other hand
or 50 cycles
high resistan
from 3 to
istance to c
d at the sam
e of penetr
an be derive
e results o
cles. The res
wever, the d
means the r
0 cycles.
of concrete
8 MixI‐M20
densely pac
red accordi
of 100 mm a
e samples w
erature, the
on depth of
h of concre
fter exposu
thickness o
e. So, the re
d, mix 5 wit
s. Similar tre
nce to chlor
4 mm du
hloride pen
me value be
ration depth
ed according
f chloride
sults reveale
iffusion coef
resistance o
at normal
x 190/10‐SF III‐
ked concret
ng to the m
and thicknes
were exposed
e rapid chlor
f concrete. F
ete sample
re to 50 cy
of the samp
eal value of
th slag ceme
end can be
ide migratio
ue to autoc
etration eve
efore and af
h, testing pe
g to the Fick
diffusion of
ed that the d
fficient of m
f mix 21 is a
conditions
Mix 21‐M20/10‐SF
e
methods de
ss of 50 mm
d to autoclav
ride migratio
Figure 6.11
s after 50
ycles, mix 1
ples was 50
penetration
ent showed
observed f
on was obse
claving for
en after hyd
fter autoclav
eriod and th
k’s laws of di
f concrete
diffusion coe
mix 21 was 2
about 15 tim
and after a
Mix 23
Normal
50 cycle
III‐M20/10
113
escribed in
m were cut
ving for 50
on test has
shows the
cycles of
8 had the
0 mm; the
n of mix 18
a little bit
or mix 19.
erved. The
50 cycles.
drothermal
ving for 50
he applied
iffusion for
at normal
efficient of
2.47 x 10‐13
mes higher
utoclaving
l
es
Effect of
Figure 6
for 50 cy
6.6 D
6.6.1 M
The expe
each co
strength
confirme
calcium
strength
pressure
chemica
C/S ratio
formed
strength
properti
after aut
which w
quartz p
The incr
particles
strength
Chloride diffusion coefficien
t
f hydrotherm
6.12: Chlorid
ycles
iscussion
Mechanica
erimental te
ncrete mix
h of mix 18,
ed the sam
silicate hy
h. When ex
e, C‐S‐H is
al and mecha
o of the mat
which has c
h [Bezerra, 2
ies at high t
toclaving fo
was perhaps
powder may
rease of stre
s with incre
h retrogress
0
5
10
15
20
25
30
35
40x 10 ‐1
3 (m
2/sec)
mal conditio
de diffusion
al propertie
est results o
has a distin
made with
me behavior
ydrate (C‐S‐
xposed to
converted
anical prope
trix. For mix
crystalline st
2011]. In spit
emperature
or 50 cycles.
not sufficie
y be limited
ength after
easing the t
ion is obser
Mix 5
III‐M20/10
ns on the pr
n coefficient
s.
of compress
nct pattern
OPC, can be
. Hydration
‐H) which i
high tempe
into severa
erties of con
x 18, becaus
tructure, hig
te of the ad
e, the compr
This could
nt to modify
to the first
5 cycles ma
emperature
rved. Bažan
Mix 18
I
roperties of
of concrete
ive strength
of strength
e significant
of Portlan
is the main
erature, pa
al other pha
ncrete. The
se of the hig
gh specific m
dition of qu
ressive stren
be due to t
y the C/S ra
stage of aut
ay be also d
e. However,
nt has notice
8 Mix
I‐M20
densely pac
e at normal
h after hydro
h loss or ga
tly observed
d cement p
n compone
articularly c
ases, which
produced p
gh initial C/S
mass, high p
uartz powde
ngth of mix
he low cont
tio of the w
toclaving, w
due to acce
with increa
ed similar b
x 19
0/10‐SF II
ked concret
conditions
othermal ex
in. A severe
d. The result
produced ca
nt respons
combined w
h markedly
hases depe
S ratio, lime
permeability
er, which ma
18 is reduce
tent of the a
whole matrix
where the str
lerating the
asing the au
behavior, at
Mix 21
I‐M20/10‐SF
e
and after a
xposure indi
e loss of th
ts of reboun
alcium hydr
ible of the
with saturat
change the
nd mainly o
e‐rich phase
y and low co
ay have the
ed from 72
added quart
x. The influe
rength was
e hydration
utoclaving c
t saturated
Mix 23
Norm
50 cy
III‐M20/10
114
utoclaving
cated that
he residual
nd number
roxide and
e concrete
ted vapor
e physical,
on the bulk
s could be
ompressive
pozzolanic
to 44 MPa
tz powder,
ence of the
increased.
of cement
cycles, the
steam. He
mal
ycles
Effect of hydrothermal conditions on the properties of densely packed concrete 115
found a decrease in compressive strength to about 50 % of the original strength [Bažant, 1996].
The residual strength depends mainly on the maximum temperature, bulk C/S ratio, exposure
period and concrete type. Ghosh and Nasser found a significant strength loss after exposure to
high temperature and pressure [Ghosh, 1996]. They attributed that to a gradual deterioration of
the binding matrix with the rise in temperature. At high temperature, chemical transformation of
the gel happened, the dense C‐S‐H gel is subjected to changes and form a weak matrix which
responsible for the loss of strength at high C/S ratio.
Partial replacement of OPC with fine fly ash and silica fume seemed to prevent the strength
retrogression to a certain degree. The results of mix 19 confirm this claim. The residual strength
after 50 cycles of autoclaving was increased from 82 to 95 MPa. The reason for that may be due to
the hydrothermal conditions which accelerate the pozzolanic reaction between quartz powder,
fine fly ash and silica fume with calcium hydroxide. As a result of this reaction, excess of C‐S‐H
phases were formed which is responsible for the strength of concrete. Furthermore, the produced
C‐S‐H has low C/S ratio because of the high silica content of the bulk materials. This is because
when exposed to hydrothermal treatment, silica‐rich phases are transformed to other phases with
higher strength. Poon et al. argued the strength increase to the formation of tobermorite (two or
three times stronger than normal C‐S‐H gel) which is formed by the reaction between fly ash and
lime at high temperature [Poon, 2001]. The results of mix 19 are in good agreement with Khan
who studied the effect of fly ash on the residual compressive strength after exposed to 200 °C. He
found that the residual compressive strength increases with raising the percentage of fly ash
[Khan, 2010]. Another reason could also explain the increased compressive strength. The
interfacial transition zone in concrete usually plays a major role in controlling the mechanical
properties. This is because the high concentration of calcium hydroxide and the high porosity of
this zone. By addition of pozzolanic materials and due to the hydrothermal conditions the
pozzolanic reaction is markedly accelerated in this zone. Thus, denser phases are formed on the
aggregate surfaces which enhance the bond strength between cement paste and aggregate. The
rebound number results for mix 19 showed approximately the same behavior of the compressive
strength results. After hydrothermal exposure, the rebound number increased to about 112 % of
its original value. Similar results were achieved by Lehmann [Lehmann, 2009]. He reported that
compared to ambient conditions, the autoclaved samples showed better mechanical properties.
This was attributed to the high degree of hydration and to the more homogeneous and denser
microstructure.
The use of slag cement revealed low resistance to strength retrogression, as can be shown from
the results of mix 1. However, some of the previous works showed that the use of slag cement
Effect of hydrothermal conditions on the properties of densely packed concrete 116
enhances the concrete resistance to fire and to elevated temperature [Khoury, 2000; Poon, 2001].
This contradictory of the results with literature may be due to several reasons. Most of the
investigations tested slag concrete after exposure to elevated temperature only without pressure.
However, the presence of moisture has a significant influence on the compressive strength. It is
believed that water in concrete soften the cement gel, or weaken the surface forces between gel
particles, thus reducing the strength [Cheng, 2004]. Moreover, most of these investigations tested
the slag concrete after exposure to one cycle only. In addition, the concrete composition is totally
different from that tested in literature which certainly affects the results. In this investigation, the
strength of mix 1 with slag cement dramatically reduced with increasing the autoclaving cycles.
The final residual strength of mix 1 after hydrothermal treatment for 50 cycles was about 78 % of
the original value without autoclaving. Similar observation has been found from the results of
rebound number. The final rebound number for mix 1 was reduced to about 87 % of its original
value. Similar conclusion was found by Xi [Xi, 1997]. He noticed a strength retrogression of about
50 % of the original value for autoclaved cement paste made with blended cement in which the
slag content was about 67 %.
Combination of slag cement with fine fly ash (mix 5) exhibited improvement in compressive
strength after hydrothermal exposure. This is in accordance with the results concluded by other
researchers [Bažant, 1996; Xu, 2001]. The explanation was the increased Van der Waal’s forces as
a result of the cement gel layers moving closer to each other. It can be also said that the addition
of 30 % fine fly ash as well as quartz powder along with the slag cement is sufficient to ensure low
C/S ratio of the matrix. Consequently, silica‐rich phases are formed which is associated with high
strength. Additionally, the autoclaving process encourage the dissolution of quartz grains which in
turn produces a better cohesion between fillers and cement paste [Lehmann, 2009].
Consequently, a significant increase in the compressive strength takes place. On the other hand,
the use of silica fume along with slag cement (mix 7) prevents the strength retrogression, but no
significant increase in the final strength has been observed. Despite the strength increase of silica
fume concrete after 5 autoclaving cycles, a gradual decrease in strength with further autoclaving
for 10, 15 and 50 cycles took place. The final compressive strength was about 103 % of its original
value. The reduction in strength of concrete is probably attributable to the high C/S ratio of the
bulk, owing to the low amount of the added silica, about 10 % of the cementitious materials.
Khoury attributed the relatively low performance of silica after temperature exposure to the
probability of micro‐cracks development [Khoury, 2000].
Effect of hydrothermal conditions on the properties of densely packed concrete 117
At low w/b ratio, interesting features can be observed. Even after exposing to 50 autoclaving cycles,
the compressive strength of mix 23 was continuously increased with increasing the autoclaving
cycles. The results of compressive strength and rebound number assured this conclusion. The
residual compressive strength of mix 23 was 117 MPa which represented 129 % of its original value.
The possible reason is the greater percentage of unhydrated fly ash and cement particles due to the
low w/b ratio. At high temperature and in the presence of moisture, the hydration of unhydrated
cement grains is increased. In addition, the pozzolanic reaction of fine fly ash with the generated
lime from the hydration of cement is accelerated. Thus, more C‐S‐H with low C/S ratio is formed
which enhances the final compressive strength. Additionally, the microstructure became denser due
to the replacement of CH with C‐S‐H. In addition, due to the low C/S ratio of the bulk, the
hydrothermal treatment resulted in silica‐rich calcium silicate hydrate phases which normally
associated with high strength. Moreover, because of the low w/b ratio, the porosity is very low.
Nevertheless, the additional pozzolanic C‐S‐H fills the micro‐cracks, if any, and blocks the small
pores, which results in more homogeneous microstructure. Due to all these reasons, the
compressive strength of mix 23 showed a significant increase with autoclaving. Compared to mix 23,
mix 21 made with silica fume and fine fly ash revealed similar performance after hydrothermal
exposure. These results agree with Lawson who reported that reducing the w/b ratio enhanced the
residual compressive strength after exposure to 200 °C, particularly in combination with silica fume
[Lawson, 2000]. It is interesting to note from the results of the compressive strength that the
maximum increase for mix 21 was after autoclaving for 15 cycles, while for mix 23 it was directly
after 5 cycles. This could probably explained by the high reactivity of silica fume compared to fine fly
ash. In the case of silica fume, it consumed the produced calcium hydroxide from the hydration of
cement before autoclaving or at the first stages of it. On the other hand, during the first 10 cycles of
autoclaving, the slag cement hydration began to accelerate and more calcium hydroxide was
produced, which consumed by pozzolanic materials in the latter stages of autoclaving. However, for
mix 23, excess of calcium hydroxide could be found in the matrix, and with autoclaving the
pozzolanic reaction was accelerated, which directly resulted in an increase in compressive strength
in the early autoclaving stages.
6.6.2 Porosity
At high temperature, it is difficult to measure the porosity of concrete because it needs special
techniques, but it can be measured easily after cooling down. So, the change in porosity and pore
size distribution due to hydrothermal conditions can only be determined if they have irreversible
changes on the concrete microstructure. Measurement of porosity gives a clear description of the
pore structure and its changes due to hydrothermal treatment. In this investigation, the mercury
Effect of hydrothermal conditions on the properties of densely packed concrete 118
intrusion porosimetry has been used to measure the porosity of concrete before and after
autoclaving for 50 cycles.
The results showed a noticeable increase in the porosity of mix 18 made with OPC after autoclaving
for 50 cycles as expected. The transformation of lime‐rich C‐S‐H phases at high pressure and
temperature resulted in weak and porous phases such as α‐C2SH, which leads to a large increase in
the porosity. In addition, the pozzolanic reaction between quartz powder and calcium hydroxide
which favored to happen at these hydrothermal conditions may resulted in phases with high C/S
ratio. This is because of the low amount of the added quartz powder which is not sufficient to
prevent the formation of the weak and porous C‐S‐H phases. The optimum content to prevent the
formation of these phases is about 40 % [Mindess, 2003; Neville, 2004], while the added content
was only about 15 %. However, partial replacement of OPC with pozzolanic materials (mix 19)
reduced the porosity after autoclaving for 50 cycles. This can be attributed to the probability of
reducing the C/S ratio of the bulk system by the addition of silica‐rich materials as well as the
accelerated pozzolanic reaction which consumes the calcium hydroxide crystals. Nevertheless, the
residual porosity of mix 19 after autoclaving for 50 cycles is still higher than the original one and
increased from 6.2 % to about 7.9 %. On the other hand, mix 5 with 30 % fine fly ash and slag
cement with slag content of about 68 % showed an interesting behavior. After hydrothermal
treatment for 50 cycles, the total porosity reduced from 7 % to 5.3 %. This can be explained as
follow; the hydration of slag cement is very slow and produces low amount of calcium hydroxide
which is one of the main sources for calcium ions in the pore structure. With hydrothermal
treatment, the hydration process of slag is significantly accelerated and resulted in generation of
much more C‐S‐H which densifies the microstructure and reduces the porosity volume and sizes. In
addition, the system contains high amount of silica‐rich materials because there are many sources
for silica; from slag, from quartz, and from fly ash. This high silica concentration in the system
ensured the formation of C‐S‐H phases with low C/S ratio either from pozzolanic reaction of silica
with calcium hydroxide or from the transformation of the existed amorphous phases to crystalline
phases due to hydrothermal treatment. The formed phases have low porosity because of their low
density. Similar trend can be clearly recognized for mix 23 with low w/b ratio. Mix 23 with the same
composition as mix 5 behaved in the same way. The total porosity reduced from 4.9 % to 2.65 %
with autoclaving for 50 cycles. However, mix 21 with both silica fume and fine fly ash showed
approximately no change in the total porosity due to autoclaving. The causes of these phenomena
are not easily explainable. In the next chapter, the effect of hydrothermal treatment on the
properties of cement paste and the transformation of different C‐S‐H phases will be explained in
details. From the above discussion and results it can be noticed that compared to pure heat
exposure, hydrothermal treatment leads to significant decrease or increase in concrete porosity
Effect of hydrothermal conditions on the properties of densely packed concrete 119
depending mainly on the chemical composition of the bulk system. However, when the concrete is
subjected to high temperature only, a significant increase in porosity occurs. The increase in
porosity may be due to the release of adsorbed water and the coarsening of pore structure. In the
case of pure heat, a strong temperature gradient could be generated. This temperature difference
encourages the moisture escape from the substance during heating which causes an additional
moisture gradient. If the heating rate is rather high, the generated moisture differences may lead to
additional stresses and micro‐cracking or explosive spalling as in the case of fire. This influence is
vanished with autoclaving process which maintains stable moisture content inside the specimen,
thus reduces the micro‐cracking and stresses due to combined moisture and temperature gradient
[Müller, 2008].
The experimental results of capillary porosity (30 nm ‐ 10 µm) reflected some interesting features.
The OPC concrete showed a large increase in the capillary porosity due to hydrothermal treatment
for 50 cycles. The main reason for that as previously discussed is the formation of lime‐rich C‐S‐H
phases. In contrast, notable reduction in the capillary porosity can be clearly observed from the
results of mix 19. In spite of the increase of the total porosity of mix 19 after autoclaving for 50
cycles, the capillary porosity is significantly reduced from 4.5 to 2.4 %. The addition of fine fly ash
and silica fume is responsible for this reduction. The hydrothermal treatment accelerated the
pozzolanic reaction of silica fume and fine fly ash with calcium hydroxide. And as a consequence of
this reaction the calcium hydroxide is replaced by additional C‐S‐H which densifies the
microstructure and modifies the pore size distribution. This result is in agreement with the results of
Shekarchi [Shekarchi, 2002], who found the volume of fine pores tend to increase with autoclaving.
Mix 5 with slag cement and fine fly ash showed approximately similar behavior. The capillary
porosity is reduced from 3.5 % to 1.7 % due to autoclaving for 50 cycles. The main factor responsible
for the porosity reduction is the pozzolanic reaction which resulted in pore size refinement, matrix
densification, paste aggregate interface refinement and the consumption of calcium hydroxide. With
addition of pozzolanic materials, large amount of calcium hydroxide was transformed into C‐S‐H;
while the remaining CH tends to form smaller crystals compared to those in the OPC concrete. The
pozzolanic reaction normally occurs in the capillary voids and the generated C‐S‐H fills the capillary
pores or reduces its size. On the other hand, fine fly ash revealed better behavior than silica fume at
low w/b ratio after hydrothermal exposure. Although the capillary porosity of mix 21 with both silica
fume and fine fly ash nearly remained the same after hydrothermal treatment (about 1.9 %), mix 23
showed remarkable reduction of capillary porosity to about the half (from 2.96 to 1.44 %). This may
be because of the developments of micro‐cracks in the case of silica fume. In both cases, the
capillary porosity was very low (< 2 %). This may be attributed to the low w/b ratio, where the
capillary porosity is low and a considerable part of cement grain remains unhydrated. At high
Effect of hydrothermal conditions on the properties of densely packed concrete 120
temperature and pressure, the hydration of cement particles as well as the pozzolanic reaction were
accelerated, which significantly resulted in more reduction in capillary porosity.
Additional comments should be made concerning the pore size distribution. Autoclaving process
generated an obvious change in concrete microstructure and pore size distribution. Figure 6.13
presents the pore size distribution of some concrete mixes at normal conditions and after
autoclaving for 50 cycles. It can be observed that concrete pore structure varied very much with
autoclaving for different concrete mixes. For mix 5, the volume of pores with size lower than 1 µm
was reduced significantly due to hydrothermal conditions. However, mix 18 showed an obvious
enlargement in all pore sizes. This is due to the transformation of C‐S‐H gel into crystalline products
with high density and smaller solid volume which leads to an increase in the porosity and shrinkage.
The presence of silica‐rich materials such as fly ash and silica fume promote the formation of silica‐
rich C‐S‐H phases with smaller change in the density. Additionally, as a result of the accelerated
pozzolanic reaction, the cracks and small pores were filled with the produced C‐S‐H, as can be seen
from the pore size distribution of mix 19. An apparent decrease in the volume of pores in the range
of 10 to 100 nm of mix 19 after hydrothermal treatment for 50 cycles occurred. For mix 21, although
the changes of total pore volume remain rather small, a significant change of the cumulative
distribution in comparison with normal conditions can be observed. Mix 21 showed an increase in
the volume of pores in the size range of about 50 nm to 0.8 µm (capillary range), which
fundamentally affects the transport properties through concrete. However a little bit decrease in
the size smaller than 60 nm took place. Mix 23 with low w/b ratio showed a quite increase in the
volume of pores with size larger than about 140 nm. However a considerable decrease of the pores
with sizes lower than about 140 nm can be significantly observed. The reason for that as explained
above may be due to the late hydration of non‐hydrated cement particles as well as the acceleration
of pozzolanic reaction which resulted in pore refinement and denser microstructure. These results
are in good agreement with those obtained by [Poon, 2001]. He reported that a significant decrease
in porosity and average pore diameter was observed by addition of pozzolans as compared to the
pure OPC concrete.
Effect of hydrothermal conditions on the properties of densely packed concrete 121
Figure 6.13: The pore size distribution at normal conditions (dotted) and after autoclaving for 50
cycles (continuous)
6.6.3 Durability
6.6.3.1 Permeability
Two methods were used to measure the permeability of concrete; water penetration depth and air
permeability. The results of water penetration showed a significant increase in the depth of
penetrated water for all mixes due to autoclaving. The penetration for mix 18 reached about 80 mm
after autoclaving for 15 cycles, whereas it was about 18 mm before autoclaving, more than 4 times.
This is due to the increase in total porosity and the modification of the pores connectivity. Similar
trends but with lower values of water penetration depth can be apparently observed for all mixes
0
5
10
15
20
25
30
35
0.001 0.01 0.1 1 10 100
Cumulative volume (m
m3/g)
Pore radius (micron)
Mix 5 (III‐M20/10)
0
10
20
30
40
50
60
70
0.001 0.01 0.1 1 10 100
Cumulative volume (m
m3/g)
Pore radius (micron)
0
5
10
15
20
25
30
35
40
0.001 0.01 0.1 1 10 100
Cumulative volume (m
m3/g)
Pore radius (micron)
0
2
4
6
8
10
12
14
0.001 0.01 0.1 1 10 100
Cumulative volume (m
m3/g)
Pore radius (micron)
0
2
4
6
8
10
12
14
16
18
0.001 0.01 0.1 1 10 100
Cumulative volume (m
m3/g)
Pore radius (micron)
Mix 18 (I)
Mix 19 (I‐M20/10‐SF) Mix 21 (III‐M20/10‐SF)
Mix 23 (III‐M20/10)
Effect of hydrothermal conditions on the properties of densely packed concrete 122
even with low w/b ratio after hydrothermal treatment for 15 cycles. An observation here should be
clarified; in spite of the reduction of porosity of mix 23 (for example) with autoclaving, the water
penetration depth was increased. For this mix, the penetration depth increased from 5 to 22 mm
after autoclaving for 15 cycles. This could be interpreted as follow; the surfaces of pores are
normally rough and narrow for penetration while the heating causes smoothening of these surfaces,
thus the surface energy is decreased. This makes the average width of the necks governing the flow
to increase many times, and in particular the necks of gel pores to be widened [Bažant, 1997]. This
influence simplifies the passage of water through the necks, meanwhile, the pore volume of necks
still remains negligible, and therefore, no remarkable influence of the increased width of the pores
necks on the total porosity can be noticed. Another physical explanation was reported by Bažant,
the low density C‐S‐H phases are transformed to relatively high density C‐S‐H which shrinks and
therefore opens free spaces for the water penetration [Bažant, 2005]. Though the water
penetration depth was significantly increased after autoclaving for 15 cycles, some mixes such as 5,
21 and 23 could be evaluated as impermeable concrete under aggressive conditions, since the
penetration depth is less than 30 mm according to Neville [Neville, 2004].
In the contrary to the results of water penetration, were the results for air permeability, while the
only exception was mix 18. Spite all mixes showed reduction in air permeability, mix 18 with OPC
showed a significant increase at all levels of autoclaving. The reason for that as mention in the
previous paragraph was the significant increase in porosity, in particular the capillary porosity.
Partial replacement of OPC with silica fume and fly ash resulted in a noticeable decrease in air
permeability. This may be due to pozzolanic reaction of fly ash and silica fume with CH which
produces new pozzolanic C‐S‐H. This C‐S‐H blocks the pores and tightens the aggregate‐paste
interface which leads to a reduction in air permeability. At low w/b ratio, in spite of the increase of
water penetration depth, very low air permeability has been detected after autoclaving for 15 and
50 cycles. This could be explained as follow; although the high penetration of water into concrete
happened, that does not mean a continuous passage of water from one side to the other side
existed. On the other hand, for air permeability measurement, the passage should be continuous
from one surface to the other face of the concrete specimens.
6.6.3.2 Absorption (Capillary suction)
The absorption of concrete is strongly depending on the size and connectivity of capillary pores in
the concrete microstructure [Hilsdorf, 1995]. It is stated that if the total porosity is higher than 20 %,
the capillary pores become connective, while at lower porosity the transport of fluids and gases into
concrete is governed by the nano‐pores in the C‐S‐H microstructure [Bentz, 2000]. Therefore, the
characteristics of the formed C‐S‐H phases have an important role in controlling the movements of
Effect of hydrothermal conditions on the properties of densely packed concrete 123
gases and liquids through concrete. The experimental results showed that most mixes with w/b
ratio of 0.42 suffered an increase in the absorption coefficient, however some of these mixes
exhibited significant decrease in capillary porosity with autoclaving. The results of capillary suction
test of mix 18 showed a large increase in the absorption coefficient after autoclaving for 15 cycles
from0.32 to 0.50 kg/m2 h0.50. This is due to the presence of high concentration of calcium hydroxide
in the pore structure which could participate in the transformation of C‐S‐H gel into lime‐rich C‐S‐H
phases with high porosity. In spite of the addition of pozzolanic materials, mix 19 showed an
increase in absorption coefficient after hydrothermal treatment for 15 cycles from 0.1 to 0.2 kg/m2
h0.50. On the other hand, mixes with slag cement showed a little bit increase in absorption
coefficient after hydrothermal exposure. The reason for that may be lying in the influence of
autoclaving process in altering the pores sizes and modifying their opening without increasing the
total porosity volume. At low w/b ratio, the results showed very small (negligible) changes in the
absorption coefficient due to exposing to autoclaving for 15 cycles. This is totally agreed with the
results of capillary porosity. The large number of unhydrated cement and pozzolanic materials
particles of mixes with low w/b ratio (mix 21 and 23) affect the capillary porosity and transport
properties intensively. At w/b of 0.42, the microstructure and interfacial transition zone contains
more capillary pores and less unhydrated materials than those with low w/b (0.27). By autoclaving,
the widening of pores opening is more dominant with w/b ratio of 0.42, however, the refinement
and blocking of pores by accelerated hydration of non‐hydrated particles is more meaningful with w/b
ratio of 0.27. In addition, the phases transformation has an important role in this concern as will be
seen in the following chapter.
6.6.3.3 Chloride diffusion
The resistance of concrete to chloride ion ingress is a crucial factor influencing the concrete
durability [Yang, 2002]. The chloride penetration measurement gives indirectly a good indication
about the permeability and pore structure of concrete. The diffusion of chloride took place mainly
through the porous system. The rate of diffusion depends mainly not only on the porosity volume
but also on the physical characteristics of the capillary pore structure [Stanish, 2000]. The
experimental results of chloride ingress into concrete after hydrothermal exposure showed an
increase of chloride diffusion coefficient of most mixes; the only exception is mix 23. As expected
and as has been found from aforementioned experimental tests, mix 18 showed the highest
degradation due to hydrothermal treatment. After autoclaving for 50 cycles, the penetration of
chloride increased and reached the other face of the samples, which mean high rate of diffusion.
Significant enhancement was observed by addition of fly ash and silica fume as can be seen from the
results of mix 19 in both cases; at normal conditions and after autoclaving for 50 cycles. The same
trend can be easily noticed for mix 5. Compared to mix 18 with OPC cement, the use of slag cement
Effect of hydrothermal conditions on the properties of densely packed concrete 124
combined with fine fly ash (mix 5) resulted in denser microstructure and formation of silica‐rich
phases or at least reduces the formation of lime‐rich phases to a certain extent, which can explain
the high resistance to chloride diffusion. In addition, hydrothermal exposure accelerated the
pozzolanic reaction with calcium hydroxide which resulted in formation of pozzolanic C‐S‐H phases
with lower porosity compared to normal C‐S‐H phases. Nevertheless, the chloride penetration depth
was increased for mixes 5 and 19, though the total porosity and capillary porosity were significantly
reduced. The reason for that as previously mentioned may be due to the enlargement of the pores
openings which has a negligible effect on the total porosity, but have an important influence on
penetration of water into concrete. At low w/b ratio, silica fume concrete (mix 21) exhibited a
marginal increase in chloride diffusion with autoclaving for 50 cycles. This may be attributed to the
generation of some micro‐cracks associated with the use of silica fume at high temperature. The
chloride diffusion coefficient of mix 21 is still very low after autoclaving, about 2.47 x 10‐13 M2/sec.
However, mix 23 with fine fly ash and without silica fume showed very high resistance to ingress of
chloride before and after autoclaving. This is basically due to the very low content of capillary pores
as well as the dense and homogenous interfacial zone. Due to its spherical shape and its small size,
fine fly ash enhances the packing of particles, particularly near the aggregate surfaces. With
autoclaving, the hydration of cement and the pozzolanic reaction are significantly accelerated and
resulted in much more dense microstructure and homogeneous interfacial zone. In addition, the
hydration of unhydrated cement particles consumes more water, thus the capillary porosity is
reduced, the pore sizes are lowered and the capillary pores connectivity is interrupted. As a result,
concrete with fine fly ash and w/b ratio of 0.27 showed very low chloride diffusion coefficient even
after hydrothermal treatment, it was 4.9 x 10‐13 M2/sec.
Studying the influence of autoclaving on the properties of cement paste 125
7. Studying the influence of autoclaving on the properties of cement paste
7.1 General
Until now, very little information is available concerning the behavior of HPC with mineral admixture
under hydrothermal conditions according to the author knowledge. In chapter 6, the influence of
hydrothermal conditions up to 200 °C and 15.5 bars on the mechanical properties, porosity and
durability of densely packed high performance concrete has been studied. However, to obtain a
widespread information regarding the concrete behavior in these conditions, one should test large
variety of concrete because the presence of aggregate. Subsequently, for fundamental
understanding of the concrete performance, at the first step, it is reasonable to focus on the
ingredients of concrete which is mostly affected by these conditions, namely cement paste. So, this
chapter is focus on the effect of autoclaving with a temperature of 200 °C and saturated vapor
pressure of 15.5 bars for several cycles on the properties of cement paste incorporating various
cementitious materials.
In this chapter, several systems comprising OPC, CEM III/B, silica fume, normal and fine fly ash and
quartz powder have been prepared and tested to analyze their performance after hydrothermal
exposure. Because of the sensitivity of the testing conditions to micro‐cracking formation due to
liberated heat from cement hydration, isothermal calorimeter was used to measure and control the
hydration heat development of all cement pastes at normal conditions. In addition, compressive
strength and porosity of cement pastes have been implemented in order to study the influence of
autoclaving on the paste properties. Moreover, to investigate the microstructural changes due to
the hydrothermal treatment, scanning electron microscopy (SEM) has been performed.
Furthermore, an attempt to understand the chemistry of autoclaving process was carried out by the
help of thermogravimetric analysis (TGA) and energy dispersive X ray spectroscopy (EDX).
7.2 Mixes and tests
In order to study the behavior of cement paste after hydrothermal exposure, 10 mixes with different
compositions have been prepared and tested. Table 7.1 shows the composition and proportions of
different cement pastes. All cement pastes were named with the same names of the concrete mixes
in the previous chapters with the same cementitious materials compositions. Details of the
materials properties and tests procedures were explained in chapter 3. The hydration heat flow of
all mixes has been determined using isothermal calorimeter. On the other hand, the pastes were
mixed and the moulds were cast. After 24 hours the specimens were demoulded and cured under
water at 20 ± 1 °C for 56 days. After the designed curing period, samples were exposed to
Studying the influence of autoclaving on the properties of cement paste 126
autoclaving for 50 cycles at temperature of 200 °C and saturated vapor pressure of 15.5 bars. In
addition to compressive strength, porosity of different mixes was measured using helium
pycnometry at normal conditions and after hydrothermal treatment for 50 cycles. Helium
pycnometry was used also to determine the changes in the pastes density due to autoclaving. SEM,
EDX, and TGA were also used to study the microstructure changes and calcium hydroxide content in
both cases; at normal conditions and after autoclaving with 50 cycles.
Table 7.1: Composition of cement pastes (%)
Mix Cement type Cement content FA Fine FA SF QP w/b SP
Mix 1 CEM III/B 90 10 0.42 0.7
Mix 2 CEM III/B 63 27 10 0.42 1.5
Mix 5 CEM III/B 63 27 10 0.42 1.4
Mix 7 CEM III/B 81 9 10 0.42 0.9
Mix 18 CEM I 90 10 0.42 0.87
Mix 19 CEM I 58.5 22.5 9 10 0.42 1.4
Mix 21 CEM III/B 60.3 22.5 7.2 10 0.27 4
Mix 23 CEM III/B 63 27 10 0.27 3
CEM I CEM I 100 0.30 0.8
CEMIII CEM III/B 100 0.30 0.4
7.3 Hydration of cement paste
7.3.1 Hydration heat
Cement hydration is accompanied with release of a considerable amount of heat and rise in
temperature (exothermic process). The rate and amount of hydration heat depend mainly on the
chemical composition of the mix. Because of the relatively low thermal conductivity of concrete, it
acts as insulator, a temperature gradient between inside and outside the concrete member may
exist. This could lead to thermal stresses and undesired thermal micro‐cracking [Wang, 2010]. In
addition, the significant heat liberation during cement hydration causes thermal shrinkage at early
ages. The thermal shrinkage is hindered by external restraints as well as by the internal restraint
which results from the difference in thermal expansion coefficient between cement and aggregate.
Thus, cracking possibility is very high because the low tensile strength of concrete and the high
thermal shrinkage [Liwu, 2006]. These detrimental effects associated with the release of hydration
heat have a crucial influence on durability and mechanical properties of concrete. It is also
responsible for loss of strength at latter ages and micro‐cracking [Sioulas, 2000]. The generated
micro‐cracks are very critical when concrete subjected to high temperature because it works as
cracks propagation. Therefore, it is important to exactly study the hydration heat development of
different cement mixes in order to select the appropriate mixture for a certain application.
Studying the influence of autoclaving on the properties of cement paste 127
In this investigation, isothermal calorimeter (MC‐CAL/100P) was used to determine the rate of
hydration heat flow as well as the cumulative heat of different cement pastes. A small amount of
each mix (about 10 g) was mixed for 90 seconds and immediately was put in the calorimeter at 20
°C. The measurement started directly after putting the specimen in the calorimeter and extended
for 7 days. Results of the hydration heat of all cement pastes are illustrated in Figure 7.1. It can be
observed that the trends of heat evolution of mixes with CEM I are similar. Two peaks can be
observed. The initial peak can be attributed to both exothermic wetting and the early reaction of
cement with water to form ettringite [Taylor, 1997]. A dormant period with very low heat evolution
followed the initial peak. Thereafter, the reaction is significantly accelerated and the released heat
was increased rapidly until it reaches the main peak, which attributed to the reaction of C3S with
water to form C‐S‐H and CH. After the main peak, the heat release is gradually decreased due to the
slow reaction at the late stage. Compared to CEM I, the addition of 10 % quartz to cement
postponed the peak of mix 18 for about 1.8 hours. The peak of mix 19 was a little bit higher than
that of CEM I and Mix 18. Nevertheless, the arrival time of the highest hydration exothermic rate
was markedly delayed by 3.56 hours due to the addition of 25 % of fine fly ash and 10 % silica fume.
It is also observed that, superplasticizer content caused a retardation effect on hydration. When
superplasticizer increases from 0.8 (CEM I paste) to 1.4 % (Mix 19), the dormant period was
extended by 4 hours. Cumulative heat hydration curves over a 7 days period are presented in
Figure 7.2. The total hydration heat of OPC pastes varied as supplementary materials added. It
reached about 350 J/g after 7 days for mix with neat OPC. Addition of 10 % quartz powder reduced
the total heat to about 306 J/g (mix 18). For mix 19, combination of 25 % fine fly ash and 10 % silica
fume resulted in additional decrease in the cumulative liberated heat to about 287 J/g.
Figure 7.1: The rate of hydration heat development of cement pastes
0
1
2
3
0 10 20 30 40
Heat flow (mW/g)
Time (hours)
CEMI
CEMIII
Mix 1
Mix2
Mix 5
Mix 7
Mix 18
Mix 19
Mix 21
Mix23 (III‐M20/10)
(III‐M20/10‐SF)
(I‐M20/10)
(I)
(III‐SF)
(III‐M20/10)
(III‐FA)
(III)
Studying the influence of autoclaving on the properties of cement paste 128
Figure 7.2: Cumulative hydration heat of different cement pastes
The measurement of hydration heat of slag cement pastes showed some interesting features as can
be observed from Figure 7.1. After the dormant period, the main peak of cement paste made with
pure CEM III/B was about 40 % of OPC. It was occurred approximately at the same time. Similar to
mix 18, the addition of 10 % quartz powder to slag cement (Mix 1) resulted in a decrease of the
height of the main peak, although it took place at the same time. Compared to mixes with fly ash
(mix 2 and mix 5), the addition of 10 % of silica fume (mix 7) accelerated the main peak and
significantly decrease the dormant period. Fly ash fineness seemed to have an important influence
on the hydration heat development. For mix 2 with normal fly ash, the main peak occurs earlier than
that of mix 5 with fine fly ash. Nevertheless, both mixes have approximately the same peak height.
At low w/b ratio, the hydration of cement is significantly retarded. In addition to the lack of water,
high dosage of superplasticizer has a crucial effect on retarding the hydration. The main peak of mix
21 and 23 was reached after about 21 and 27 hours respectively. The results of total liberated
hydration heat for slag cement pastes can be shown in Figure 7.2. The total heat of slag cement
paste after 7 days was 240 J/g which represents about 68 % of that of OPC. By partial replacement of
cement with quartz, silica fume and fly ash, gradual decrease of the cumulative heat was attained (mixes
1, 2, 5 and 7). Interestingly, mixes 21 and 23 showed very low cumulative heat after 7 days of hydration
(121 J/g), which represents only 35 % of that of OPC. These results agree with the conclusions reached
by some other researchers [Kolani, 2012; Merzouki, 2013].
7.3.2 Discussion
Predicting the potentiality of thermal cracking of cement‐based materials at early ages as well as the
development of thermal stresses due to hydration heat of cement requires a deep knowledge of
0
50
100
150
200
250
300
350
400
0 50 100 150 200
Cumulative heat (J/g)
Time (hours)
CEM I
CEM III
Mix 1
Mix 2
Mix 5
Mix 7
Mix 18
Mix 19
Mix21
Mix 23
(III‐M20/10)
(III‐M20/10)
(III‐M20/10‐SF)
(III‐SF)
(I)
(I‐M20/10‐SF)
(III‐FA)
(III)
Studying the influence of autoclaving on the properties of cement paste 129
thermal characteristics of cements. The hydration heat of cement depends mainly on the particle
size distribution, w/b ratio, temperature and the chemical composition of the mix [Taylor, 1997]. At
the first glance, the experimental results showed that the hydration heat of OPC is higher than that
of slag cement. The main peak of cement paste with 10 % quartz (Mix 18) is very close to that of
neat OPC. This may be attributed to the filler effect of quartz which may provide additional
nucleation sites for the hydrates from OPC (seeding effect) [Deschner, 2012]. However, partial
replacement of OPC with fine fly ash and silica fume (mix 19) resulted in a significant extension of
the dormant period and quite shifting of the main peak to the right side. For mix 19, the PH is
considerably decreased due to the absorption of calcium ions on both fly ash and silica fume
particles. Thus, the calcium concentration in the pore solution is reduced which retarded the
hydration, or by other words extended the dormant period. These results match the consequences
reported by [Langan, 2002]. Further explanation can be given by the increased amount of
superplasticizer for mix 19 which has significant retardation effect. Superplasticizer does not affect
the value of the peak, but it extended the dormant period, and thus the main peak is retarded,
shifted to the right direction. The total heat evolution of OPC pastes are approximately proportional
to the OPC content as can be clearly shown from Figure 7.2.
Compared to OPC, the blended cement hydration is more complex due to the presence of different
chemical and physical phenomena in addition to the hydration of cement such as filler effect and
pozzolanic reaction. Contrary to silica fume and fly ash, slag is a cementing material that can be
react by itself with water, but its hydration is very slow [Wang, 2010]. Because of its slow hydration
rate, slag is used in concrete mixes, mass concrete in particular, in order to alleviate the high early
strength and mitigate the risk of thermal cracking. The reactivity of slag depends basically on the
alkalinity of the pore solution [Lothenbach, 2011]. So, the presence of clinker with slag in CEM III/B
is of vital importance to produce suitable structural product. Because of the low reactivity of slag,
the hydration of the clinker portion in slag cement is accelerated due to the availability of sufficient
water for hydration [Merzouki, 2013]. The results of heat flow rate confirm this assumption. The
main peak of CEM III/B occurs roughly at the same time of that of OPC or even quite earlier. The
heat flow flux revealed that the length of dormant period is shortened and the main peak was
attained rapidly due to the addition of silica fume (mix 7) compared to CEM III paste. This may be
attributed to the very small size of silica fume particles which act as nucleation sites [Kadri, 2009].
However, by addition of fly ash, two main effects were coexisting. First, due to the spherical shape
of its particles, it works as excellent filler. Thus, more water liberated and available for accelerate
the hydration. The second effect is the low calcium ions concentration in the pore solution due to
the increased amount of water. Therefore, the dormant period is prolonged. Compared to fly ash
pastes, the main peak of silica fume paste is accelerated. The influences of all supplementary
Studying the influence of autoclaving on the properties of cement paste 130
materials in the first day are attributed to their filler effect only, because the pozzolanic reaction
with calcium hydroxide needs more time to take place [Lothenbach, 2011].
In the case of low w/b ratio, it is clear that the hydration rate is extremely reduced. This is to be
expected for several reasons. The free space for the growth of hydration products is limited because
of the low w/b ratio. Furthermore, due to the low w/b ratio, less water is available for hydration of
cement particles. Moreover, the use of pozzolanic materials along with low water content reduced
the contact area between cement particles and water, thus the hydration rate is decreased [Wang,
2010]. In addition, the use of low w/b ratio requires high amount of superplasticizer in order to
achieve desirable workability. This leads to notably retardation of the hydration. Results of mixes 21
and 23 with w/b ratio of 0.27 showed very long dormant periods and very low peaks. The low peaks
which mean low hydration rate can be attributed to the lake of water available for hydrating the
cement particles, whereas the extension of dormant period may be due to the increased amount of
superplasticizer as mentioned before. Compared to mix 23 with fine fly ash only, the dormant
period of mix 21 with both fine fly ash and silica fume was shortened. This may be due to the effect
of silica fume as discussed earlier. However, the main peak of mix 23 came very late, after about 27
hours. This is may be due to many parameters such as low w/b ratio, use of slag cement, high
amount of superplasticizer and the use of fly ash.
7.4 The influence of hydrothermal treatment on cement pastes
In this part, the effect of autoclaving for 50 cycles with temperature of 200 °C and saturated vapor
pressure of 15.5 bars on compressive strength, porosity, density and microstructure of cement paste
will be presented.
7.4.1 Compressive strength
Compressive strength tests were carried out on 20 mm cubes. After 24 hours, the cubes were
demoulded, and then cured for 91 days under water at temperature of 20 ± 1 °C. After 56 days of
adding the water to the pastes, 3 cubes from each mix were exposed to autoclaving for 50 cycles at
temperature of 200 °C and saturated vapor pressure of 15.5 bars. Then, the cubes were allowed to
naturally cool down. Thereafter, the compressive strength test was performed on the samples at
age of 91 days. Figure 7.3 shows the results of compressive strength of cement pastes without
autoclaving (Normal) and after autoclaving for 50 cycles. Without autoclaving, it is clear that all
mixes have compressive strength in the range of 70 to 80 MPa, the exception is mixes 21 and 23
with low w/b ratio which have high strength. At w/b ratio of 0.42, the addition of normal fly ash
reduces the compressive strength as can be seen for mix 2. On contrary, the addition of silica fume
significantly enhanced the compressive strength (mixes 7 and 19). Mix 21 with w/b ratio of 0.27 and
Studying
with bo
conditio
showed
After au
noticed.
dropped
hydrothe
OPC and
replacem
with aut
autoclav
made w
seemed
compres
large de
addition
strength
strength
same co
autoclav
Figure 7
for 50 cy
0
20
40
60
80
100
120
Compressive stren
gth (MPa)
g the influen
oth fine fly
ns (about 1
quite lower
toclaving fo
The compr
d (strength r
ermal treatm
d 10 % qua
ment of OPC
toclaving. It
ving on com
with neat CE
to be non‐
ssive strengt
ecrease in st
of fly ash,
h increase wa
h of mix 21
omposition b
ving (about 4
7.3: Compre
ycles at age
Mix 1
III
nce of autocl
ash and si
110 MPa). H
compressiv
r 50 cycles,
ressive stren
retrogressio
ment (abou
artz powder
C with fine f
t increased
mpressive str
M III was a
sufficient to
th reduced
trength with
either norm
as gained. A
was reduce
but without
4 %). It incre
essive stren
e of 91 days
Mix 2 M
III‐MIII‐FA
laving on the
ilica fume e
owever mix
ve strength, a
large chang
ngth of cem
on). It reduc
t 68 %). Sim
r, the reduc
fly ash and
from 83 to
rength is qu
bout 33 %.
o prevent th
from 74 to
h addition o
mal or fine,
At low w/b ra
d from 109
t silica fume
eased from 9
ngth of cem
s
ix 5 Mix 7
M20/10 III‐SF
e properties
exhibited th
x 23 with th
about 94 MP
ge in the valu
ment paste m
ced from 78
milar influen
ction was ab
silica fume
94 MPa. Fo
uite similar.
The additio
he strength
56 MPa wit
of silica fum
not only pr
atio, the situ
to 96 MPa
e exhibited
94 to 98 MPa
ment pastes
7 Mix 18
I I‐M
s of cement p
he highest
he same com
Pa.
ues of comp
made with p
8 MPa at no
nce can be r
bout 65 %.
showed an
or mixes wi
The strengt
on of 10 % o
retrogressio
th autoclavi
e (about 33
evented the
uation is a lit
with autoc
small increa
a.
at normal
Mix 19 M
M20/10‐SF III‐M
paste
compressive
mposition bu
pressive stre
pure OPC (C
ormal condit
recognized f
In contrast
increase in
ith slag cem
th retrogres
of quartz po
on as can b
ng for 50 cy
3 %). Contra
e strength r
ttle bit confu
laving. How
ase in comp
conditions
Mix 21 Mix 2
M20/10‐SF I‐M20
e strength
ut without s
ength can be
CEM I) was
tions to 25
for mix 18 m
t, mix 19 w
compressiv
ment, the in
ssion in cem
owder to sla
e seen for m
ycles. Mix 7
ary to silica
retrogression
used. The co
wever, mix 2
pressive stre
and after a
23 CEMI
No
Au
0/10‐SF
131
at normal
silica fume
e obviously
extremely
MPa after
made with
with partial
ve strength
nfluence of
ment paste
ag cement
mix 1. The
showed a
fume, the
n, but also
ompressive
3 with the
ength with
utoclaving
CEM III
ormal
utoclaved
Studying the influence of autoclaving on the properties of cement paste 132
7.4.2 Porosity
The porosity of cement paste has been measured with two methods; helium pycnometry and water
porosity. The tests have been performed in two cases, at normal conditions and after autoclaving for
50 cycles. The pastes were prepared, mixed and cured under water at temperature of 20 ± 1 °C.
After the designed curing period, three samples from each mix were subjected to hydrothermal
treatment in the autoclave. Then, the samples were naturally cool down and transferred to the
porosity tests. All samples were freeze dried to a constant weight in order to preserve the
microstructure of the paste without any changes as possible. In addition to the autoclaved samples,
the porosity of normal specimens (without autoclaving) has been performed at the same age (91
days) in order to compare the results. The results of the measured porosity showed that both
methods (water porosity and helium pycnometry) have the same trend as can be seen in Figure 7.4
and Figure 7.5. Therefore, the following discussion will focus on the porosity measured with helium
pycnometry only. At normal conditions, the main factor control the porosity is the w/b ratio. Mixes
21 and 23 showed the lowest porosity without autoclaving which were about 21 and 24 %
respectively. Compared to mix 18 with OPC only, addition of fine fly ash and silica fume (mix 19)
significantly reduced the total porosity from 28 % to about 25 % at normal conditions.
With autoclaving for 50 cycles, the porosity of paste made with OPC (CEM I) was significantly
increased from 27 to 38 %. The same tendency can be also observed for mix 18 where the porosity
increased due to autoclaving by about 47 % of its original value at normal conditions. On the other
hand, mix 19 with partial replacement of OPC with pozzolanic materials showed an apparent
reduction in porosity after autoclaving for 50 cycles. The porosity reduced from about 25 to 20 %.
Slag cement showed a higher tendency to resist the porosity increase. The increase in porosity of
neat slag cement (CEM III) was small; it was increased from 36 to about 38 %. A slight increase in
porosity has been occurred for mix 1 with slag cement and 10 % quartz powder, it was increased
from 31 to 32 %. Similar to mix 19, the addition of pozzolanic materials resulted in reduction in the
porosity after exposing to hydrothermal treatment. Mixes 2, 5 and 7 showed reduction of porosity
by about 19, 4 and 10 % of their original values respectively. The same tendency has been revealed
for mixes 21 and 23 with low w/b ration. After hydrothermal exposure for 50 cycles, the porosity
reduced from 21 to about 15 % for mix 21 and from 24 to about 18 % for mix 23.
Studying
Figure 7
Figure 7
7.4.3 D
The den
without
order to
samples
measure
conditio
content
mix with
A small
been ob
0
5
10
15
20
25
30
35
40
45
Total porosity
0
10
20
30
40
50
Total porosity %
g the influen
7.4: Porosity
7.5: Water p
Density
nsity of all c
autoclaving
o minimize t
were finely
e the absolu
ns and afte
have the h
h OPC (CEM
increase in
bserved afte
Mix 1
Mix 1
III
III
nce of autocl
y of cement
porosity of d
cement pas
g (Normal) a
he microstr
y ground (<
ute density.
er autoclavin
highest den
I and mix 18
n density f
er autoclavin
Mix 2 Mi
Mix 2 Mix
III‐MIII‐FA
III‐M2III‐FA
laving on the
pastes mea
ifferent cem
stes has bee
and after au
uctural chan
0.063 mm).
Figure 7.6 i
ng for 50 cy
nsity at nor
8) revealed t
for paste m
ng for 50 cy
ix 5 Mix 7
x 5 Mix 7
III‐SFM20/10
III‐SF0/10
e properties
asured with
ment pastes
en determin
toclaving fo
nges due to
. Then, the
llustrates th
ycles. It is a
mal conditi
the highest d
made with n
ycles. Howev
7 Mix 18
Mix 18 M
I‐MI
I‐M2I
s of cement p
helium pyc
at 91 days
ned using h
or 50 cycles.
drying. Afte
samples we
he measured
pparently s
ions. Howev
density, abou
neat slag ce
ver, with pa
Mix 19 M
Normal
Mix 19 Mix
Normal
III‐MM20/10‐SF
III‐M2020/10‐SF
paste
cnometry
helium pycn
All samples
er drying to
ere sent to h
d density fo
hown that
ver, after a
ut 2.61 and
ement (CEM
artial replace
Mix 21 Mix 2
Autoclave
x 21 Mix 23
Autoclave
M20/10‐SF III‐M
0/10‐SF III‐M20
ometry in t
s were freez
a constant
helium pycn
or all pastes
mixes with
autoclaving
2.66 t/m3 re
M III) and
ement of sla
23 CEM I
ed
CEM I C
M20/10
0/10‐SF
133
two cases;
ze dried in
weight, all
nometry to
at normal
low water
exposure,
espectively.
mix 1 has
ag cement
CEM III
CEM III
Studying
with poz
and 2.52
consider
from 2.5
Figure 7
7.4.4 C
Calcium
on the p
measure
measure
after au
area of d
used for
under ni
the mas
hydroxid
highest
produce
addition
results o
CH, < 5 %
2.2
2.
2.3
2.
2.4
2.
2.5
2.
2.6
2.
Den
sity (t/m
3)
g the influen
zzolanic mat
2 to 2.49,
rable decrea
51 and 2.59 a
7.6: Specific
Calcium hy
hydroxide is
physical and
e the reacti
ed with the
toclaving fo
decompositi
r TGA analy
itrogen flow
ss loss betw
de content o
CH content
d about 16.
of high am
of mix 19 (ab
%. With auto
25
.3
35
.4
45
.5
55
.6
65
.7
Mix 1III
nce of autocl
terials, a sig
2.43 and 2
ase in densi
at normal co
c density (t/m
ydroxide co
s one of the
d chemical p
ivity of diff
help of ther
or 50 cycles.
ion of CH to
sis. The sam
w of 2.4 liters
ween 425 an
of all pastes.
as expecte
2 % of CH. L
ount of poz
bout 4.4 %).
oclaving, mo
Mix 2 MIIIIII‐FA
laving on the
gnificant red
2.41 t/m3 fo
ty also due
nditions to a
m3) of ceme
ontent
major prod
properties o
ferent pozzo
rmogravime
. It can estim
CaO and wa
mples have
s/hour. Calc
nd 550 °C [
. Without au
ed, about 18
Large reduct
zolanic mate
On the othe
ost mixes ga
Mix 5 MixIII‐SI‐M20/10
e properties
duction in de
or mixes 2,
to autoclav
about 2.39 a
ent pastes m
ucts of ceme
of the concre
olanic mate
tric analysis
mate CH in
ater. Approx
been heate
ium hydroxi
[Taylor, 199
utoclaving (n
8.35 %. Mix
tion of calciu
erials due to
er hand, mix
ained more C
x 7 Mix 18II SF
s of cement p
ensity took
5 and 7 r
ving process
nd 2.47 t/m3
measured w
ent hydratio
ete. Estimat
erials. Calciu
(TGA) for a
hydrated p
ximately 750
d to 900 °C
ide content
97]. Figure 7
normal), pas
x 18 with 10
um hydroxid
o their react
xes with slag
CH, the only
Mix 19 M
Norm
I‐M20/10‐SF III‐
paste
place. It red
espectively.
s took place3 for mixes 2
ith helium p
on which exe
tion of CH s
um hydroxid
all mixes at n
roducts by
0 mg of grou
C with heati
has been ca
7.7 shows t
ste with nea
0 % of quar
de content h
tion with CH
g cement pro
y exception w
Mix 21 Mix
mal Autocla
III‐M‐M20/10‐SF
duced from
At low w/
e. The densit
21 and 23 res
pycnometry
ert an impor
serves as a m
de content
normal cond
determining
und, dried pa
ng rate of 1
alculated by
he calculate
at OPC (CEM
rtz in additio
has been gain
H, as can be
oduced low
was mix 18.
23 CEM I
ave
M20/10
134
2.55, 2.49
/b ratio, a
ty reduced
spectively.
rtant effect
method to
has been
ditions and
g the peak
astes were
10 °C /min
the use of
ed calcium
M I) has the
on to OPC
ned by the
seen from
amount of
It reduced
CEM III
Studying
from 16
between
autoclav
to 12 %.
w/b ratio
Figure 7
7.4.5 C
In this p
results i
theoreti
ratio of o
Table 7.
Mix
C/S
The resu
hydrothe
tempera
Howeve
between
tobermo
0
5
10
15
20
25
Calcium hydroxide content %
g the influen
.2 to about
n CH and qu
ving for 50 c
On the oth
o of 0.42.
7.7: Calcium
C-S-H pha
art, the tran
n 100 % tra
cal calculati
oxides and t
.2: C/S ratio
Mix 1 M
1.21
ults of calcu
ermal expos
ature level u
r, for CEM
n the lime‐r
orite, hillebr
Mix 1
III
nce of autocl
13 % with a
uartz powde
ycles. For pa
er hand, mi
m hydroxide
ses transfo
nsformation
ansformatio
on of C/S r
the chemica
o of cemet p
Mix 2 Mix
0.76 0.7
lating the C
sure. At this
up to 200 °
III/B, the C/
rich phases
randite and
Mix 2 M
III‐MIII‐FA
laving on the
autoclaving f
r. However,
aste made w
xes with low
content of c
ormation
of phases h
n of the inp
atio of all c
l compositio
pastes after
x 5 Mix
76 0.93
C/S ratio ind
s level and a
C are lime‐
/S ratio afte
and silica‐r
afwilite can
ix 5 Mix 7
No
M20/10 III‐SF
e properties
for 50 cycles
for pure OP
with CEM III
w w/b ratio
cement pas
has been ca
put materia
ement past
on of the bul
autoclaving
Mix 18
2.1
icated that
according to
rich phases
er hydrother
rich phases,
n be formed
7 Mix 18
ormal Aut
I‐MI
s of cement p
s. This may
PC paste (CE
only, the CH
showed low
stes measur
lculated ass
ls into new
es has been
lk system.
g for 50 cycl
Mix 19 M
0.96 0
CEM I paste
o Figure 2.13
such as of
rmal exposu
, therefore,
. The additio
Mix 19 M
toclaved
III‐MM20/10‐SF
paste
be due to th
EM I), it reac
H content in
wer content
red with TGA
uming that
hydrotherm
n carried ou
les with 200
Mix 21 Mix
0.66 0.7
e has C/S ra
3, the predo
α C2SH, jaf
ure is about
combinatio
on of some
Mix 21 Mix 2
III‐MM20/10‐SF
he pozzolan
ched about
ncreased fro
of CH than t
A
the autocla
mal C‐S‐H ph
ut based on
0 °C and 15
23 CEM I
76 3.2
atio of abou
ominant pha
ffeite and p
t 1.38. This
on of phase
quartz to C
23 CEM I
M20/10
135
ic reaction
21 % after
om about 5
those with
ve process
hases. The
the molar
.5 bars
CEM III
1.7
ut 3.2 after
ases in the
ortlandite.
value is in
es such as
CEM I as in
CEM III
Studying the influence of autoclaving on the properties of cement paste 136
mix 18 reduces the C/S ratio of the bulk to about 2.1. In this case, hillebrandite and α C2SH may be
the predominant phases because the C/S ratio is still high. The EDX measurements emphasized this
claim. The measured C/S ratio of mix 18 after hydrothermal exposure for 50 cycles was about 1.98.
On the other hand, for mix 19 which contains both fine fly ash and silica fume, the calculated C/S
ratio is 0.96. This low C/S ratio leads to formation of the low‐lime phases such as xonotlite and
tobermorite but the formation of tobermorite phase is more likely. The formation of xonotlite is
relatively unlikely because the relatively high alumina content (8.34 mass %) which hindered the
transformation of tobermorite to xonotlite [Bade, 1992]. In addition, the autoclave temperature of
200 °C is quite low for xonotlite formation in the presence of alumina and alkalis. Compared to CEM
III/B paste, the addition of 10 % quartz powder reduces the C/S ratio to about 1.21 as can be
calculated for mix 1 after complete transformation of the bulk materials. At this level, competition
between lime‐rich phases and silica‐rich phases occur. So, for this paste a mixture of αC2SH,
hillebrandite and tobermorite may be coexisted. By addition of fly ash or fine fly ash to CEM III/B as
in mixes 2, 5, and 23, the C/S ratio drops to about 0.76. Due to the low C/S ratio and the high
aluminum content of these mixes, the predominant phases could be the formation of tobermorite
type and gyrolite type. The EDX measurement approximately revealed similar results as can be seen
in Figure 7.9. For mix 5 after hydrothermal exposure for 50 cycles, the C/S was about 0.83. However,
the addition of silica fume significantly reduces the C/S ratio to about 0.93 (mix 7) which promotes
the formation of gyrolite‐type. The formation of gyrolite is more likely than tobermorite because the
low aluminum content in silica fume compared to fly ash. Finally, the calculated C/S ratio of mix 21
made with silica fume, fine fly ash in addition to CEM III/B is about 0.66 after complete hydration.
This very low C/S ratio encourages the formation of low‐lime phases such as tobermorite, gyrolite
and truscottite.
7.5 Discussion
At normal temperature, hydration of OPC produces about 50 % of C‐S‐H and about 15 ‐ 25 % of CH
[Taylor, 1997]. The produced C‐S‐H is approximately amorphous with C/S ratio of about 2 [Hong,
2004], which is strong binding materials (by Van der Waals force of attraction) responsible for
strength of cement and concrete at temperature below 110 °C. The experimental results confirm
these claims. The calcium hydroxide of CEM I paste was about 18 %, and increased with autoclaving
to 21 %. However, after hydrothermal treatment, C‐S‐H is no longer stable, it is substituted by more
stable phases with higher crystallinity and high specific density [Bezerra, 2011]. The composition and
properties of the formed phases depends mainly on the C/S ratio, water/solid ratio (W/S) and on the
period of exposing to hydrothermal treatment [Meducin, 2008]. As a result, the compressive
strength of CEM I paste was reduced (strength retrogression) from 78 to about 25 MPa. This is
attributed to the formation of lime‐rich phases such as hillebrandite, jaffeite and α C2SH. The
Studying the influence of autoclaving on the properties of cement paste 137
formed phases have high density as has been reported by experimental density tests (Figure 7.6).
The increased density leads to a reduction in the solid volume and accompanied by an increase in
porosity and reduction in strength. The high lime content of C‐S‐H comes from two main sources;
the initial C‐S‐H which has high C/S ratio due to hydration of clinker and the high content of CH
which offer a reservoir for the calcium ions [Ramachandran, 2003]. The specific density of CEM I
paste is increased from 2.42 to 2.61 t/m3 due to autoclaving for 50 cycles. The increased density can
be considered as an indication for the formation of deleterious α C2SH and hillebrandite phases,
which reported to have a density of about 2.7 t/m3 [Taylor, 1997]. As a result, large increase in
porosity took place due to the increased density. The experimental results of porosity agree with
this assumption very well. It has been increased from 29 to 41 % with autoclaving for 50 cycles.
In spite of addition of 10 % quartz powder to the system (mix 18), the compressive strength was
reduced with autoclaving. It was decreased from 77 to 27 MPa after hydrothermal exposure for 50
cycles. The added siliceous material is not sufficient to prevent the strength retrogression. The C/S
ratio is still high and suitable to form lime‐rich phases. Confirmation for this comes from the
calculation of C/S ratio as can be seen in Table 7.2 and the observation of EDX in Figure 7.9. The C/S
ratio of mix 18 was around 2 after autoclaving for 50 cycles. The formed phase at this level is alpha
dicalcium silicate hydrate and hillebrandite, which crystallize as dense rectangular tablets with high
porosity and low strength [Taylor, 1997]. The density of mix 18 increased from 2.45 to 2.66 t/m3
with autoclaving for 50 cycles as can be seen in Figure 7.6. The formed lime‐rich phases with high
density increased the shrinkage which resulted in huge increase in porosity as can be shown in the
results of porosity (Figure 7.4). The SEM images of the surface of the polished specimens at age of
91 days in both cases normal and after autoclaving for 50 cycles can be shown in Figure 7.8. At
normal conditions, higher concentration of ettringite, monosulphate and the oriented crystals of
calcium hydroxide are existed, which is generally considered a weaker component of the hydration
products. However, after autoclaving, SEM photos clearly showed very porous microstructure.
The incorporation of large amount of silica‐rich materials, fly ash and silica fume in addition to 10 %
quartz powder, resulted in not only preventing strength retrogression, but also enhancement in the
compressive strength after autoclaving as can be noticed from the results of mix 19. The
compressive strength increased from 83 to about 94 MPa after hydrothermal treatment for 50
cycles. The density measurement showed little change due to hydrothermal treatment. It reduced
from 2.45 to 2.44 t/m3. These are probably due to the low C/S ratio of the bulk (C/S equals 0.96
according Table 7.2), which prevents the formation of lime‐rich phases and instead silica‐rich phases
such as 1.1 tobermorite, xonotlite and gyrolite are formed. These phases have quite low density
which leads to dense microstructure with low porosity. The porosity of mix 19 is reduced from 25 %
Studying the influence of autoclaving on the properties of cement paste 138
to about 20 % after autoclaving. The low CH content also may have an influence on reducing the
porosity and enhancing the strength, because it was replaced with C‐S‐H. Thus, additional amount of
C‐S‐H is added to the system. Both low clinker content in the bulk and the incorporation of
pozzolanic materials are responsible for reducing the amount of CH which normally associated with
high porosity and weak strength. Compared to mix 18, mix 19 exhibited lower porosity after
hydrothermal exposure. The porosity of mix 19 is about the half of mix 18 after autoclaving.
Figure 7.8 shows the SEM images which revealed dense microstructure of mix 19 (normal), with
non‐reacted spherical fly ash particles embedded in the dense cement paste. After autoclaving, very
dense and homogeneous microstructure is formed with partially reacted fly ash covered with C‐S‐H
phases. These observations indicated how slow the pozzolanic reaction of fly ash with CH is. The
results of calcium hydroxide content of mix 19 showed that it was increased with autoclaving. This
may be because the slow reaction of pozzolanic materials as well as the low solubility of CH,
particularly with increasing the temperature [Taylor, 1997]. On the other hand, the transformation
of phases depends mainly on the C/S ratio of the bulk. Proof for that is from the results of mixes 18
and 19. At normal conditions, both mixes have a density of about 2.45 t/m3. However after
autoclaving, mix 18 with higher C/S ratio exhibited specific density of about 2.66 t/m3, whereas the
specific density of mix 19 with lower C/S ratio was reduced to about 2.44 t/m3. These results clarify the
important role of C/S ratio on the properties and transformation of C‐S‐H phases after autoclaving.
Similar results on the influence of siliceous materials on the strength of cement paste were reported by
Jing et al. [Jing, 2008]. Who attributed the enhancement of strength to the formation of tobermorite and
disappear of lime‐rich phases.
Pure slag cement paste (CEM III/B) showed apparent strength retrogression after autoclaving. It was
reduced from 71 to about 48 MPa after autoclaving for 50 cycles. Similar results were reported by Xi
[Xi, 1997]. He found that the compressive strength of slag cement with slag content of about 67 %
was reduced to about 50 % after autoclaving with 200 °C and 15.5 bars. Despite slag cement (CEM
III/B) contains relatively high amount of silica, the compressive strength is reduced with autoclaving.
The C‐S‐H formed from the hydration of slag cement has quite high C/S ratio (about 1.7). In this
level, lime‐rich phases such as afwilite, alpha dicalcium silicate and hillebrandite could be formed
[Meller, 2005; Bezerra, 2011]. The strength retrogression observed from the experimental results
indicated the major presence of the lime‐rich phases. The quite high C/S and the alkalinity of the
pore solution are such that αC2SH and hillebrandite are dominant. Furthermore, the density and
porosity measurements showed quite increase after hydrothermal exposure. This is because the
high density of the formed phases leads to coarsening the pore structure which increases the
Studying the influence of autoclaving on the properties of cement paste 139
porosity and reduces the strength. Similar results but with lower values were noticed for mix 1 with
addition of 10 % quartz powder to slag cement system. The compressive strength reduced from 74
to about 56 MPa. The reason for that may be the quite high C/S ratio, although it is lower than that
of paste made with pure slag cement. The calcium ions are supplied from two main sources: one
from clinker hydration and the second from the hydration of slag itself [Kolani, 2012]. Regarding CH
content, both pastes (CEM III and mix 1) have the similar initial CH content, about 5 %. While, after
hydrothermal exposure, the CH content was about 12 and 8 % for mixes CEM III and mix 1
respectively. The calcium hydroxide content relies mainly on both the hydration degree of the
clinker and on the progress of slag hydration. The first produces CH, whereas the latter consumes the
CH. The reduced amount of mix 1 is due to the addition of quartz powder. This effect emphasized the
pozzolanic reactivity of quartz under hydrothermal treatment when it is finely ground.
The incorporation of fly ash in combination with slag cement significantly enhanced the compressive
strength after hydrothermal exposure. The compressive strength increased by about 18 % and 10 %
for mixes 2 and 5 respectively. This may be attributed to the formation of 1.1 tobermorite which has
been accelerated with increasing the aluminum content [Matsui, 2011]. This phase is known to
enhance and stabilize compressive strength [Kyritsis, 2009]. In addition, the strength reducing phase
αC2SH will not be formed anymore because of the low C/S ratio. Beaudoin reported that fly ash
performance at high temperature is similar to that of pure silica, can apparently reduce the C/S ratio
and prevent the formation of αC2SH [Beaudoin, 1979]. Figure 7.8 shows the SEM of mix 5 before and
after autoclaving. The non‐reacted fly ash sphere can be clearly seen. This confirms the slow
hydration of slag cement and the very low rate of pozzolanic reaction. This is attributed to the low
alkalinity in the pore structure, since the reaction of slag is activated by the liberated CH. The results
from TGA for CH content showed that the amount of liberated CH was about 4 % before autoclaving
and increased to about 6.5 % after hydrothermal exposure. After autoclaving, SEM of mix 5 showed
the formation of C‐S‐H, probably tobermorite phase as reported in literature [Garbev, 2004].
Another evidence for the possibility of tobermorite formation can be easily detected from the
results of EDX. The C/S of pore solution was about 0.94 and reduced to 0.83 after autoclaving which
is suitable for the formation of silica‐rich phases such as tobermorite. Taylor stated that, C/S ratio in
the range of 0.8 ‐ 1 is optimum for formation 1.1 tobermorite [Taylor, 1997]. In addition, the density
of slag cement paste was apparently reduced by addition of fly ash, either normal or fine. The
density of mix 2 and 5 after hydrothermal treatment was 2.49 and 2.43 t/m3. This could be considered
an evidence for formation of tobermorite which has a specific density of around 2.44 [Taylor, 1986].
These results reflected the ability of fly ash to prevent the strength retrogression by formation of
more stable and strong phases. The main benefit of fly ash comes from the high content of silica and
aluminum, that encourage the formation of 1.1 tobermorite which responsible for reducing the
Studying the influence of autoclaving on the properties of cement paste 140
porosity and permeability [Kyritsis, 2009]. These results are in good agreement with Hilsdorf
[Hilsdorf, 1986], who confirmed the ability of fly ash to prevent strength retrogression. On the other
hand, conflict results were obtained about the behavior of silica fume. Despite the porosity and
density of paste made with silica fume was reduced, strength retrogression took place. Similar
results about the behavior of silica fume was found by Luke [Luke, 2004], who reported that
undefined phases were formed with the use of silica fume. In addition, alpha dicalcium silicate were
detected which could explain the strength retrogression in the case of silica fume. These effects can be
attributed to the low amount of aluminum in the bulk solution, and the possibility of microcracking.
At low w/b ratio, interesting results were obtained. Considerable strength retrogression for mix 21
was observed. The strength was decreased from 109 to 96 MPa (about 13 %) due to autoclaving for
50 cycles. On contrary, mix 23 with the same composition but without silica fume exhibited very
good resistance to strength retrogression. Not only the strength retrogression is prevented, but also
a little bit increase in the compressive strength was achieved after exposed to 50 autoclaving cycles.
It was increased from 94 to 98 MPa with autoclaving. This difference in strength can be attributed to
the formation of different phases in both cases (mixes 21 and 23). At hydrothermal conditions, the
system and the formed phases were very sensitive to any change in the chemical composition of the
pore solution. The high content of aluminum incorporated by the addition of fly ash enforced the
formation of more stable phases (mix 23). However, the addition of silica fume resulted in
significant strength retrogression which can be attributed to the low aluminum content in the
system. In addition, it can be also attributed to the high probability of micro‐cracking formation in
the case of silica fume, particularly with hydrothermal exposure. Although both mixes (21 and 23)
exhibited difference performance concerning the compressive strength, the density and porosity are
similar. The density of mix 21 and 23 was reduced from 2.51 and 2.59 to 2.39 and 2.47 t/m3
respectively after hydrothermal exposure. Similar trend can be observed for porosity results. At
normal conditions, very low porosity was attained due to the low w/b ratio. The low water content
offered small space for the cement to hydrate. The C‐S‐H can form only if enough free space is
available [Taylor, 1997]. In addition, the added pozzolanic materials work as filler, thus more
reduction in porosity can be achieved. After autoclaving, a significant decrease in porosity took
place. The hydrothermal treatment lead to formation of silica‐rich C‐S‐H phases which resulted in
dense microstructure as can be observed from the results of mixes 21 and 23. The porosity of mixes
21 and 23 reduced from 21 and 25 % at normal conditions to 15 and 18 % respectively after
autoclaving for 50 cycles. On the other hand, the results of calcium hydroxide content of mixes 21
and 23 shows that liberated calcium hydroxide in the pore solution was small, which indicated the
low hydration degree. However after hydrothermal treatment, small increase in the CH content of
both mixes with low w/b ratio occurred.
Studying
Figure
autoclav
g the influen
7.8: SEM
ving for 50 c
nce of autocl
measurem
cycles (right
laving on the
Mix
Mix 19
ents for ce
t)
e properties
5 (CEMIII‐M
Mix 18 (CEM
9 (CEMI‐M20
ement pas
s of cement p
20/10)
MI)
0/10‐SF)
tes at nor
paste
rmal condit
ions (left)
141
and after
Studying
Figure 7
g the influen
7.9: EXD an
nce of autocl
alysis of ce
laving on the
ment at nor
M
e properties
rmal conditio
Mix 5 (CEMII
Mix 5 (CEM
M
Mix
s of cement p
ons and afte
I‐M20/10) n
MIII‐M20/10)
Mix 18 (CEMI
x 18 (CEMI) a
paste
er autoclavi
ormal
) autoclaved
I) normal
autoclaved
ing for 50 cy
142
ycles
Applying the optimized concrete in hot water tank 143
8. Applying the optimized concrete in hot water tank
8.1 Introduction
In this investigation and as previously discussed, optimized concrete mixes have been prepared and
tested in the laboratory and they showed stable properties regarding concrete strength and
durability after hydrothermal exposure. However, for hot water tank, the concrete has to be tested
in the real conditions, where it will be implemented and subjected to different loading conditions. In
addition, it is important from the safety point of view to study the failure mode of concrete tank in
such aggressive conditions. This chapter presents the experimental results of the preliminary stage
of producing a concrete tank to store hot water and steam at temperature higher than 100 °C based
on the results of this thesis.
8.2 Concrete mixture
In these preliminary experiments, mix 23 with small modifications has been used for constructing
the concrete tank models. This mix has been chosen because of the low amount of hydration heat
as well as its high durability and stability after hydrothermal exposure for 50 cycles. Table 8.1 shows
the mix composition and the properties of the used concrete. Figure 8.1 and Figure 8.2 show the
concrete mixing and the measurement of fresh concrete properties.
Table 8.1: Composition and properties of the used concrete for prliminary experiments
Composition
CEM III /B 32.5 (kg/m3) 224
Fine fly ash (kg/m3) 96
Aggregate (4 – 8) (kg/m3) 885
Aggregate (2 – 4) (kg/m3) 546
Sand (0 – 2) (kg/m3) 485
Quartz sand (kg/m3) 82
Quartz powder (kg/m3) 45
Superplasticizer (kg/m3) 6
Water (kg/m3) 96
Total (kg/m3) 2465
Rheological properties
Fresh concrete density (kg/m3) 2470
Flow diameter (cm) 47
Temperature of fresh concrete (°C) 18.3
Air content (%) 1
Applying
Hardene
Compre
Splitting
Water p
Total po
Figure 8
Figure 8
g the optimiz
ed concrete p
essive strengt
g tensile stren
penetration d
orosity (91 da
8.1: Prepara
8.2: Flow dia
zed concrete
properties
th (91 days)
ngth (91 days
epth (91 day
ays)
ation for con
ameter and
e in hot wat
(M
) (M
s) (m
(%)
ncrete mixin
air content
er tank
Pa)
Pa)
m)
)
g
of the usedd concrete
85
5.
6
6.
5
.2
.9
144
Applying
8.3 C
A cylindr
has been
As can b
are fixed
surface a
Figure 8
8.4 Fi
In the e
installing
tank and
outside
capacity
been use
heating
surface
parallel
tempera
moment
the conc
and out
g the optimiz
Concrete ta
rical tank m
n built as ca
be seen from
d in both sid
and steel pla
8.3: Hot wat
irst experi
experiment,
g the upper
d on the ou
the tank. In
y of 10 KW to
ed to measu
rate (1 ‐ 2 °C
have been o
to each oth
ature differe
t with high te
crete tensile
tside the co
zed concrete
ank model
odel with di
an be seen in
m the figure,
des. In addit
ates in order
er concrete
iment
the concre
steel plate,
uter surface
n addition, a
o heat up th
ure the temp
C/min). The
observed an
her as can b
ences throug
ensile stresse
strength, th
oncrete tank
e in hot wat
l
iameter of 8
n Figure 8.3
both sides
tion, a dens
r to prevent
tank mode
ete tank mo
thermocoup
e as well in
a pressure g
he water has
perature dis
results of th
nd the wate
be shown fro
gh the tank
es on the co
erefore crac
k reached 7
er tank
850 mm, hei
. This tank h
of the tank
sifying mate
any escape
l
odel has be
ples have be
order to m
gauge has b
s been insta
stribution in
he test show
er began to
om Figure 8
wall. This t
ncrete wall.
cking occurre
72 °C as m
ght of 600 m
has been co
are opened
rial has bee
of water an
een partly f
een fixed on
measure the
been also im
lled. On the
the concret
wed that at 9
escape. All
8.5. These cr
temperature
The generat
ed. The temp
measured wi
mm and wal
onstructed w
. Therefore,
en installed b
nd vapour.
filled with w
the bottom
temperatur
mplemented.
other hand
te wall. The
90 °C some
these crack
racks are fo
e difference
ted tensile st
perature diff
th thermoc
ll thickness o
without reinf
, two thick s
between the
water (20 °
m and on the
re changes
. Electric h
, infra‐red c
test started
cracks at th
s are longit
rmed due t
leads to te
tresses are h
ference betw
couples. The
145
of 125 mm
forcement.
steel plates
e concrete
C). Before
top of the
inside and
eater with
camera has
d with high
e concrete
udinal and
o the high
emperature
higher than
ween inside
e Infra‐red
Applying
camera
as can b
been de
been ob
Figure 8
Figure 8
g the optimiz
measureme
be seen in fig
etected. Mor
served.
8.4: Prepara
8.5: Longitud
zed concrete
ents showed
gure 6. Rega
reover, no m
ation for the
dinal cracks i
e in hot wat
also the hig
arding concr
micro‐cracki
first experim
in the wall of
er tank
gh temperat
rete perform
ng or any d
ment
f the concre
ture differe
mance, no d
etrimental i
ete tank mod
nce through
eterioration
nfluence on
del due to tem
hout the con
n in concrete
n concrete s
mperature g
146
ncrete wall
e itself has
surface has
gradient
Applying
Figure 8
8.5 Se
To cope
two‐laye
23) with
addition,
tempera
thermoc
of heatin
continuo
that poin
widened
plate cre
energy (t
steam w
stored e
cracking
vapour h
g the optimiz
8.6: Temper
econd exp
with the pro
er tank mode
out reinforce
, a thermal i
ature gradie
couples. In th
ng, the temp
ous heating,
nt, the steel
d. In addition
eated. Cons
the height o
was continuo
energy inside
has been ob
has been occ
zed concrete
rature distrib
periment
oblem of tem
el has been
ement, whil
nsulating ma
nt. The tem
his experime
perature of w
the tempera
l plate was d
n, the densify
equently, st
of the steam
ously escapi
e the tank.
bserved in in
curred.
e in hot wat
bution on th
mperature g
developed.
e the outer
aterial has b
mperature b
ent, low hea
water inside
ature was ra
deformed an
ying materia
team with h
column reac
ng for more
After coolin
nternal or ext
er tank
e concrete
gradient (tem
The inner la
layer was m
been fixed on
between the
ting rate has
the tank rea
aised slowly
nd the dista
l has expand
high pressur
ched about 1
e than 15 m
ng down, th
ternal concr
tank measu
mperature m
ayer was ma
ade of norm
n the surface
e two layers
s been appli
ached 155 °C
to 162 °C an
nce betwee
ded and a ga
re is sudden
15 meters as
minutes whic
he concrete
rete layers. In
ured using th
moment) and
de of the op
mal concrete
e of the tank
s has been
ed (10 °C/ho
C as can be s
nd the press
en it and the
ap between c
nly escaped
s can be sho
ch reflect th
tank has be
n addition, n
he Infra-red
d longitudina
ptimized con
with reinfor
k in order to
measured
our). After s
een in Figure
sure reached
e concrete su
concrete wa
with large a
own in Figure
he high amo
een examin
no diffusion o
147
d camera
al cracking,
ncrete (mix
rcement. In
reduce the
also using
ome hours
e 8.7. With
d 6 bars. At
urface was
ll and steel
amount of
e 8.7). The
ount of the
ed and no
of water or
Applying
g the optimiz
The ta
The te
Figure 8.7
zed concrete
ank is totally
mperature w
Large
: The secon
e in hot wat
y insulated f
was continu
amount of e
nd prelimina
er tank
rom all sides
ously increa
energy and s
ary test on tw
s to reduce t
ased with he
steam has b
wo-layer ho
temperature
ating and re
een released
ot water con
e difference
eached 155 °
d
crete tank m
148
s
°C
model
Applying
8.6 Fu
Based o
hot wate
large cyl
hot wate
several w
tank, the
problem
optimize
prestres
totally in
the curr
can be s
seen in F
Figure 8
g the optimiz
uture work
n the result
er tank mod
lindrical tank
er tank mod
weeks. It ca
e steel plate
m of the stee
ed concrete
sed steel in
nsulated fro
ent stage, t
een in Figur
Figure 8.9.
8.8: Internal
zed concrete
k
ts of this inv
del, a new re
k model (pro
del will be su
an be also u
will be repl
el plate. The
without re
n order to k
m outside in
he internal
e 8.8. Moreo
layer of the
e in hot wat
vestigation a
esearch proje
ototype) wit
ufficient to f
used for pro
aced with a
e tank will b
inforcement
keep the co
n order to re
layer of the
over, the mo
e future conc
er tank
and on the r
ect has been
th dimensio
feed one ho
oducing elec
concrete do
be also two‐
t, while the
oncrete wall
educe the te
e tank has b
ould for the
crete tank m
results of th
n planned an
n of 1800 x
ouse (100 m2
tricity by us
ome (half sp
layered; the
e outer one
ls under com
emperature
been constru
concrete do
model made
he prelimina
nd already s
1250 mm w
2) with the r
sing Peltier
phere) becau
e internal on
will be of
mpression.
difference a
ucted with t
ome has bee
e of the optim
ry experime
started. In th
will be perfo
required hot
effect. In th
use of the de
ne will be m
normal con
The tank w
and therma
thickness of
en fabricated
mized conc
149
ents of the
his project,
rmed. This
t water for
he planned
eformation
ade of the
crete with
will be also
l losses. At
70 mm as
d as can be
rete
Applying
Figure 8
g the optimiz
8.9: The fab
zed concrete
ricated mou
e in hot wat
uld for concr
er tank
rete model tto be used iinstead of ssteel plate
150
Conclusions and recommendations 151
9. Conclusions and recommendations
9.1 Conclusion
The research project presented within this PhD‐thesis was focused mainly on studying the possibility
of developing a dense high performance concrete mixture for a concrete tank to store solar thermal
energy in hot water and steam at high temperature up 200 °C and pressure of 15.5 bars. In the
targeted tank, the leakage of water and vapour is prevented by implementing a very dense high
performance concrete. The optimized concrete should exhibited high efficiency and stability after
exposing to various autoclaving cycles. An important subject in this respect is the stability of C‐S‐H
phases after hydrothermal exposure with several cycles. Many factors influence the behaviour of
concrete under these hydrothermal conditions. Regarding transport properties through the
optimized concrete, the mineralogical properties of concrete constituents are of more concern.
However, chemical composition of the concrete mixture is considered the basic parameter with high
impact on the stability of C‐S‐H phases.
The first step of this investigation is to develop a high density concrete mixture. Increasing the
packing density is considered an excellent strategy to get an optimized concrete mix. This can
achieved via three main mechanisms. The first one is maximizing the packing density of solid
particles by applying the Ideal Fuller curve for aggregate and fine materials grading. The second
mechanism is designing a dense cement matrix taking into consideration several items such as
physical and chemical properties of fine materials. The third mechanism is densifying the interfacial
transition zone which is the locus of micro‐cracking and affects the concrete durability and
mechanical properties.
The experimental work has been divided into three main parts. In the first one, a high density
concrete mixture has been optimized and tested. In this concern, 23 mixes with more than 560
standard cubes and 90 standard cylinders have been prepared and tested. The second part of this
investigation focused on the effect of autoclaving with 200 °C and 15.5 bars on properties of the
optimized concrete. Mechanical properties including compressive strength, tensile strength and
rebound number as well as concrete porosity have been measured at normal conditions and after
autoclaving with numerous cycles. Regarding the concrete durability, the main three mechanisms of
ingress of gases and liquids through concrete; permeability, absorption and diffusion, have been
measured before and after autoclaving for 50 cycles. In the third part, 10 different cement pastes
have been prepared and tested in order to deeply understand the effect of hydrothermal conditions on
characteristics and stability of C‐S‐H phases. In this concern, EDX, TGA and SEM measurements have
been used to study the changes in pastes morphology and properties due to autoclaving for 50 cycles.
Conclusions and recommendations 152
Based on the experimental results, the following conclusions can be drawn:
Concrete mixture optimization:
The Ideal Fuller curve is different from the well‐known Fuller parabola. It has lower coarse
aggregate content and higher fine materials content.
By applying the Ideal grading curve, it is possible to produce HPC with superior properties using
only 312 kg/m3 of cementitious materials.
In spite of the use of low amount of cementitious materials (312 kg/m3), with w/b ratio of 0.27,
the compressive strength reached about 100 MPa, while the elastic modulus was more than 50
GPa. This can be directly related to the high packing density of the mixture.
The maximum porosity of concrete mixes was 10 % for mix with OPC and without any
supplementary materials, which reveal the important role of packing density on concrete
porosity. However, with replacing part of OPC with 25 % fine fly ash and 10 % silica fume (mix
19), the total porosity reduced to 6 %. On the other hand, a total porosity of 3 % has been
achieved by combination of high packing density and low w/b ratio.
A very low capillary porosity was obtained for all mixes compared to tradition concrete and
HPC. In particular, mix 21 with w/b ratio of 0.27 has a capillary porosity of lower than 2 % which
is in the range of UHPC.
According to Neville, all concrete mixes can be considered impermeable under aggressive
conditions (water penetration depth < 20 mm). For mix 23, it reached 3 mm only.
The use of supplementary materials with low w/b ratio has reduced the chloride diffusion
coefficient of concrete 20 times lower than that of OPC.
A strong relationship has been found between the measured total porosity and mechanical
properties of concrete. However, the durability aspects were found to have clear relations to
the capillary porosity of concrete.
Generally, silica fume is more effective in improving the durability and strength of concrete in
systems with low w/b ratio than systems with high w/b ratio.
Effect of autoclaving with 200 °C and 15.5 bars on the properties of concrete:
Mixes with pure cement either OPC or slag cement showed a large decrease in compressive
strength after autoclaving for 50 cycles. However, the addition of fly ash stabilized the concrete
and prevented the strength retrogression.
At low w/b ratio, the addition of supplementary materials not only prevented the strength
retrogression, but also it increased the compressive strength to 130 % of its original value after
autoclaving for 50 cycles.
Conclusions and recommendations 153
The porosity of OPC concrete was increased by about 30 % after autoclaving. However, partial
replacement of cement with fine fly ash and silica fume reduced the increase in the porosity
after autoclaving for 50 cycles.
Combination of fine fly ash and slag cement exhibited a decrease in total porosity after
autoclaving. It reduced from 7 to 5 % with w/b ratio of 0.42. However, at low w/b ratio, it has
been decreased from 5 to 2.6 % after hydrothermal treatment for 50 cycles (mix 23).
The pore size distribution of concrete showed strong alteration due to autoclaving. The volume
of pores > 10 nm is increased with autoclaving for OPC concrete, while slag cement concrete
showed an increase in fine pore volume and reduction in big pores volume.
The air permeability test showed a decrease in permeability of most concrete mixes after
autoclaving for 15 and 50 cycles. The only exception is the OPC concrete mix (mix 18) which
exhibited a significant increase in air permeability with autoclaving.
A slight increase in water absorption coefficient of most concrete mixes was occurred due to
autoclaving for 50 cycles. Mix 23 with fine fly ash and low w/b ratio was the only exception. It
showed a slight decrease in absorption coefficient after autoclaving for 15 cycles.
The chloride diffusion coefficient of OPC concrete exhibited a significant increase after
autoclaving. However, mix 23 showed a good resistance to chloride penetration before and
after autoclaving. It exhibited a chloride diffusion coefficient of 4.29 x 10‐13 m2/s after
autoclaving for 50 cycles. Although mix 21 with both fine fly ash and silica fume showed the
lowest value before autoclaving (2.47 x 10‐13 m2/s), the chloride diffusion started to increase
after autoclaving and reached 4 x 10‐13 m2/s.
Effect of autoclaving with 200 °C and 15.5 bars on properties of cement pastes:
Similar to the results of concrete, large changes in compressive strength of cement pastes have
been occurred due to autoclaving for 50 cycles. Significant strength retrogression was found for
OPC and CEM III pastes. However, replacing part of cement with fine fly ash and silica fume
resulted in increase in compressive strength after hydrothermal treatment for 50 cycles. It
increased from 83 MPa at normal conditions to 94 MPa after treatment (mix 19).
Around 50 % increase of porosity of OPC paste has been measured after autoclaving. The
addition of pozzolanic materials significantly prevented the increase in porosity.
For OPC pastes, the autoclaving process resulted in transformation of phases to lime‐rich
phases such as portlandite, α C2SH and hillebrandite. These phases have high density, high
porosity and very low strength as revealed by the experimental measurements. In addition, the
EDX measurement confirmed the formation of these phases because of the high C/S ratio of the
OPC systems.
Conclusions and recommendations 154
Systems with high amount of supplementary materials have low C/S ratio of the bulk (< 1). The
formed phases in these systems after hydrothermal exposure are the silica‐rich phases such as
tobermorite and xonotlite which have low density, small porosity and high strength.
Fly ash and fine fly ash exhibited very high efficiency in reducing the porosity and increasing the
compressive strength of cement paste after autoclaving for 50 cycles.
SEM measurements of OPC pastes revealed the high concentration of CH, monosulphate and
ettringite before autoclaving, while a porous microstructure has been formed after autoclaving.
However, dense microstructure has been detected for mixes with high content of silica‐rich
materials even after hydrothermal treatment.
The experimental results showed the importance role of C/S ratio on the stability and properties of
the system. When it increases more than 1, weak and porous product is formed which can be
considered as a detrimental for concrete durability and sustainability. In contrast, the addition of
silica‐rich materials such as quartz, slag and fly ash reduce the C/S ratio to lower than 1, which can
be accounted as an advantageous for concrete under hydrothermal conditions.
The aluminium content in the system has an important role on phase transformation. Materials
such as fly ash which contain high amount of silica and aluminium provoke the formation of
silica‐rich phases with high strength and low porosity such as tobermorite.
9.2 Recommendations
For the sake of optimizing a high dense high performance concrete, three mechanisms are of main
concern. The first one is maximizing the packing density of solid particles. This can be achieved by
applying the Ideal Fuller curve (Figure 4.1) to enhance the packing of the system and to reduce the
required cement content (as discussed in section 4.2). Basically, increasing the packing density of
aggregate would decrease the volume of paste needed to fill up the voids and increase the amount
of additional paste that could be utilized to improve the workability. Additionally, the concrete will
have less durability problems such as permeability, shrinkage, and thermal degradation. Aggregate
as they come from the quarry do not normally have size distributions that fit the dense packing
curve, so it is important to modify the aggregate grading to meet the dense packing curve. Fine
materials such as quartz powder and quartz sand can be used to modify the grading of aggregate
especially in the fine zone under the grading curve. These materials are required also to produce
stable concrete in fresh state with good cohesion and low segregation. Increasing the range of
particle size helps to enhance the packing because systems with wide range of particle sizes have
higher packing density than systems with narrow range.
Conclusions and recommendations 155
The second mechanism to produce dense concrete is to make the cement matrix as dense as
possible (as discussed in section 4.3). In this regard, three parameters are very important. First, the
particle size distribution of cementitious materials. Cement alone has low packing density and high
porosity because of the narrow particle size distribution which makes the inter‐particle voids bigger.
However, the use of various fine materials with different particles size distribution can largely
reduce the voids content within the cementitious materials mixture. The efficiency of these
materials in filling up the voids and improving the packing depends mainly on their fineness and
particle shape. Generally, a broader range of particle size distribution would yield systems with high
packing density. The second parameter is the chemical composition of the bulk materials. Many of
concrete problems especially at high temperature come from the high content of calcium hydroxide
because it is soluble and very weak compared to calcium silicate hydrates. Therefore, it is important
to use blended cement such as slag cement as well as using pozzolanic materials to densify the
microstructure, reduce the porosity and to decrease the generated hydration heat. The third
parameter is controlling the w/b ratio to achieve both the required workability and reduce the
capillary porosity. It is recommended to take the w/b ratio lower than 0.42 to reduce the porosity
while the required consistency can be achieved by the use of superplasticizer.
The third mechanism to optimize a durable concrete is to densify the transition zone which is the
weakest zone in concrete and affects all concrete properties (as discussed in section 4.4). This zone
is formed mainly due to low packing of cement particles on the aggregate surface and also due to
the one‐sided growth of cement hydration products. To cope with the first problem, low packing
density on the aggregate surface, very fine materials such as silica fume and fine fly ash can be used
to enhance the packing on the aggregate surface. However, for one‐sided growth, we suggested a
certain sequence of adding the materials to the concrete mixer. After addition of the aggregate,
some of the mixing water should be added to make the aggregate surface wet (in the site, the
aggregate is normally wet), and then the fine materials will be added. By this sequence, fine
materials can stick well on the aggregate surface and reduce the one‐sided growth effect. On the
other hand, during the compaction of fresh concrete, segregation may occur and a thick water film
could be formed beneath the aggregate particles. Moreover, local bleeding is favoured to happen in
the transition zone and around the aggregate surface. So, it is important to use the sufficient amount
of fine materials to prevent these harmful effects by enhancing the packing due to their filler effect.
Conclusions and recommendations 156
To summarize, the following steps are recommended to design a dense concrete mixture:
Determination of the maximum aggregate size considering its effect on water and binder
content as well as on the hardened concrete properties (as discussed in page 56).
Calculating the solid materials fractions using the Ideal Fuller curve which applied for both
aggregate and binder (Figure 4.1).
Choose the aggregate grading that fit the curve to achieve the maximum packing density (Figure 4.3).
Selecting the cement type to control chemistry of the hydration products (as discussed in page 60).
Optimization of the binder proportioning (< 0.125 mm) by using various supplementary
materials, type and content, in such a way that maximum packing can be attained (granulometric
viewpoint), meanwhile, dense and durable cement matrix microstructure as well as thin and dense
interfacial transition zone can be achieved (chemical viewpoint) (section 4.3.2).
Determination of the required fillers addition (quartz sand and quartz powder) to fill the gaps
between the mixture and the targeted curve (section 4.2).
Calculating the water content from rheological, physical and chemical points of view (w/b 0.42, in order to reduce the capillary porosity as low as possible).
Adapting the superplasticizer dosage, that is compatible with the used cement, to get the
required consistency, and to enhance the packing density of fine materials.
Regarding the stability of concrete under high pressure and temperature, the chemical composition of
the bulk materials is very important. The bulk materials should be selected in such a way that the formed
phases after hydrothermal exposure must be stable and strong. For example, when ordinary Portland
cement pastes exposed to autoclaving, lime‐rich phases such as alpha dicalcium silicate and hillebrandite
predominated which increase the porosity and reduce the strength. The formation of these detrimental
phases can be avoided by adding fine silica (about 30‐40 %). So, silica‐rich materials such as fly ash and
slag can help to produce stable phases with high strength and low porosity such as tobermorite,
xonotlite and gyrolite. The calcium/silicon ratio (C/S) of the formed phases is very important and
depends mainly on the chemical composition of the input materials and on its fineness.
The aluminium content plays an important role in the formation of tobermorite and extending its
stability up to higher than 200 °C. The role of aluminium can be clarified by comparing two cases;
systems with fly ash which contains high aluminium with system of silica fume which has lower
aluminium content. In the first case, phases with high strength and low porosity are formed, while
for the second phases the direction is not clear. Some other studies detected alpha dicalcium silicate
hydrate in systems with silica fume. So, more research is needed to deeply understand the
behaviour of the systems containing silica fume under hydrothermal treatment. However, the
important role of fly ash on enhancing the concrete properties has been improved by many studied
as well as by the current investigation.
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Standards
DIN EN 197‐1:2011: Zement – Teil 1: Zusammensetzung, Anforderungen und
Konformitätskriterien von Normalzement; Deutsche Fassung EN 197‐
1:2011.
DIN EN 450‐1:2012: Flugasche für Beton – Teil 1: Definition, Anforderungen und
Konformitätskriterien; Deutsche Fassung EN 450‐1:2012.
DIN EN 13263‐1:2009: Silikastaub für Beton – Teil 1: Definitionen, Anforderungen und
Konformitätskriterien; Deutsche Fassung EN 13263‐1: 2005+A1:2009.
References 169
DIN EN 12620:2013: Gesteinskörnungen für Beton; Deutsche Fassung EN 12620:2013.
DIN EN 934‐2:2012: Zusatzmittel für Beton, Mörtel und Einpressmörtel – Teil 2:
Betonzusatzmittel – Definitionen; Anforderungen, Konformität,
Kennzeichnung und Beschriftung; Deutsche Fassung EN 934‐
2:2009+A1:2012.
DIN EN 12390‐2:2009: Prüfung von Festbeton – Teil 2: Herstellung und Lagerung von
Probekörpern für Festigkeitsprüfungen; Deutsche Fassung EN 12390‐
2:2009.
DIN 1045‐2:2008: Tragwerke aus Beton, Stahlbeton und Spannbeton – Teil 2: beton –
Festlegung, Eigenschaften, Herstellung und Konformität‐
Anwendungsregeln zu DIN EN 206‐1.
DIN EN 12390‐1:2012: Prüfung von Festbeton – Teil 1: Form, Maße und andere Anforderungen
für Probekörper und Formen; Deutsche Fassung EN 12390‐1:2012.
DIN EN 12350‐5:2009: Prüfung von Frischbeton – Teil 5: Ausbreitmaß; Deutsche Fassung EN
12350‐5:2009.
DIN EN 12350‐7:2009: Prüfung von Frischbeton – Teil 7: Luftgehalt – Druckverfahren; Deutsche
Fassung EN 12350‐7:2009.
DIN EN 12350‐6:2009: Prüfung von Frischbeton – Teil 6: Frischbetonrohdichte; Deutsche Fassung
EN 12350‐6:2009.
DIN EN 12390‐3:2009: Prüfung von Festbeton – Teil 3: Druckfestigkeit von Probekörpern;
Deutsche Fassung EN 12390‐3:2009.
DIN 1048‐5:1991: Prüfverfahren für Beton, Festbeton, gesondert hergestellte Probekörper.
DIN EN 12390‐6:2010: Prüfung von Festbeton – Teil 6: Spaltzugfestigkeit von Probekörpern;
Deutsche Fassung EN 12390‐6:2009.
DIN EN 12390‐7:2009: Prüfung von Festbeton – Teil 7: Dichte von Festbeton; Deutsche Fassung
EN 12390‐7:2009.
DIN EN 12504‐2: Prüfung von Beton in Bauwerken – Teil 2: Zerstörungsfreie Prüfung –
Bestimmung der Rückprallzahl; Deutsche Fassung EN 12504‐2:2012.
DIN EN 12390‐8:2009: Prüfung von Festbeton – Teil 8: Wassereindringtiefe unter Druck;
Deutsche Fassung EN 12390‐8:2009.
DIN EN ISO 15148:2002: Bestimmung des Wasseraufnahmekoeffizienten bei teilweisem
Eintauchen; Deutsche Fassung EN ISO 15148:2002
DIN EN 206‐1:2001: Beton – Teil 1: Festlegung, Eigenschaften, Herstellung und Konformität;
Deutsche Fassung EN 206‐1:2000.
TGL 21094‐12:1975: Prüfung des erhärteten Betons, Bestimmung der spezifischen
Gasdurchlässigkeit.
References 170
Appendices 171
11. Appendices
Composition of concrete mixes
Mix
Cementitious materials composition (wt.%)
SP (wt.%)
Aggregatekg/m3
QP kg/m3
QS kg/m3
w/b ratio
Cement FA M20 M10 SF
Type %
1 CEM III/B 100 0.7 1854 46 84 0.42
2 CEM III/B 70 30 1 1854 46 84 0.42
3 CEM III/B 70 30 1 1854 46 84 0.42
4 CEM III/B 70 30 1 1854 46 84 0.42
5 CEM III/B 70 15 15 1 1854 46 84 0.42
6 CEM III/B 70 20 5 5 0.9 1854 46 84 0.42
7 CEM III/B 90 10 0.7 1854 46 84 0.42
8 CEM III/B 65 25 10 1.1 1854 46 84 0.42
9 CEM III/B 65 12.5 12.5 10 1 1854 46 84 0.42
10 CEM III/B 65 15 5 5 10 1 1854 46 84 0.42
11 CEM I 42.5 N 100 0.87 1854 46 84 0.42
12 CEM I 42.5 N 70 20 5 5 1 1854 46 84 0.42
13 CEM I 42.5 N 70 15 15 1.8 1854 46 84 0.42
14 CEM I 42.5 N 65 12.5 12.5 10 2.2 1854 46 84 0.42
15 CEM I 42.5 N 65 15 5 5 10 1.9 1854 46 84 0.42
16 CEM I 42.5 N 90 10 1.2 1854 46 84 0.42
17 CEM III/A 65 12.5 12.5 10 1.7 1854 46 84 0.42
18 CEM I 32.5 R 100 0.87 1854 46 84 0.42
19 CEM I 32.5 R 65 12.5 12.5 10 1.4 1854 46 84 0.42
20 CEM III/B 67 12.5 12.5 8 1.8 1887 45 86 0.36
21 CEM III/B 67 12.5 12.5 8 4 1947 48 88 0.27
22 CEM III/B 70 15 15 3 1885 47 86 0.36
23 CEM III/B 70 15 15 4 1947 48 88 0.27
FA: fly ash M20: fine fly ash M10: fine fly ash SF: silica fume SP: superplasticizer
Appendi
Append
several
A‐1: Co
cycle
Compressive stren
gth (Mpa)
Compressive strength (Mpa)
ices
dix A: Mech
cycles
ompressive
0
10
20
30
40
50
60
70
80
90
100
Mix 1
0
10
20
30
40
50
60
70
80
90
100
Mix 1
hanical prop
strength of
Mix 2
1 Mix 12
0
20
40
60
80
100
120
Compressive stren
gth (MPa)
perties of co
f concrete m
Mix 3 Mix 4
Mix 13 M
Mix 20
oncrete at n
mixes at nor
4 Mix 5
Mix 14 Mix 1
Mix 21
normal cond
rmal condit
Mix 6 Mix
15 Mix 16
Mix 22
ditions and
tions and af
7 Mix 8
Mix 17
Mix 23
28 days
after 1 cycle
after autoc
fter autocla
Mix 9 Mix
28
afte
Mix 18 Mix
28 day
after 1
e
172
claving for
aving for 1
x 10
days
er 1 cycle
x 19
ys
1 cycle
Appendices 173
A‐2: Compressive strength of concrete samples at normal conditions (0 cycles) and after
autoclaving for several cycles up to 15
50
55
60
65
70
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 1
60
70
80
90
100
110
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 2
60
70
80
90
100
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 3
60
70
80
90
100
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 4
60
70
80
90
100
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 5
60
70
80
90
100
110
0 5 10 15
Compressive stren
gth
(Mpa)
Number of autoclaving cycles
Mix 6
60
70
80
90
100
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 7
60
70
80
90
100
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 8
50
60
70
80
90
100
0 5 10 15
Compressive stren
gth
(Mpa)
Number of autoclaving cycles
Mix 9
60
70
80
90
100
110
0 5 10 15
Compressive stren
gth
(Mpa)
Number of autoclaving cycles
Mix 10
Appendices 174
50
60
70
80
90
100
0 5 10 15
Compressive strength
(MPa)
Number of autoclaving cycles
Mix 11
60
70
80
90
100
110
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 12
70
75
80
85
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 13
0
50
100
150
0 5 10 15Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 14
60
70
80
90
100
110
0 5 10 15
Compressive stren
gth
(Mpa)
Number of autoclaving cycles
Mix 15
50
60
70
80
90
100
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 16
70
80
90
100
110
120
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 17
60
70
80
90
100
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 18
60
70
80
90
100
110
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 19
70
80
90
100
110
120
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 20
Appendices 175
A‐3: Results of rebound hammer for concrete mixes at normal conditions and autoclaving for several cycles
70
80
90
100
110
120
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 21
60
70
80
90
100
110
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 22
70
80
90
100
110
120
0 5 10 15
Compressive strength
(Mpa)
Number of autoclaving cycles
Mix 23
36
37
38
39
40
41
42
43
44
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 1
38
40
42
44
46
48
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 2
38
40
42
44
46
48
50
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 3
40
42
44
46
48
50
52
54
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 4
363840424446485052
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 5
38
40
42
44
46
48
50
52
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 6
Appendices 176
38
40
42
44
46
48
50
52
0 5 10 15 20
Reb
ound number
Number of autoclaving cycles
Mix 7
38
40
42
44
46
48
50
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 8
42
44
46
48
50
52
54
0 5 10 15
rebound number
Number of autoclaving cycles
Mix 13
42
44
46
48
50
52
54
56
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 14
40
42
44
46
48
50
52
54
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 15
40
42
44
46
48
50
52
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 16
44
46
48
50
52
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 17
40
42
44
46
48
50
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 18
42
44
46
48
50
52
0 5 10 15
Reb
oumd number
Number of autoclaving cycles
Mix 19
40
42
44
46
48
50
52
54
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 20
Appendices 177
A‐4: Splitting tensile strength at 91 days at normal conditions and after autoclaving for
several cycles in MPa
Mix Normal 1 cycle 15 cycles
1 3.4 3.2 2
2 4.5 4.5 4.2
3 4.6 4.6 ‐
4 5 5.1 ‐
5 5 4.8 4.5
6 3.6 3.6 ‐
7 4.3 2.6 2.57
8 4.4 3.1 ‐
9 4.8 3.7 3.5
10 4.7 3.1 ‐
11 4.2 3 ‐
12 5.2 4.2 ‐
13 5.1 5.1 ‐
14 5.7 5.5 ‐
15 3.8 4.2 ‐
16 5.5 4.2 ‐
17 4.4 3.8 ‐
18 3.8 3.4 2.8
19 4.7 5 5.3
20 5.5 5.6 ‐
21 5.9 5.6 5.5
22 5.7 5.7 ‐
23 5.9 5.7 5.9
42
44
46
48
50
52
54
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 21
42
44
46
48
50
52
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 22
40
42
44
46
48
50
52
54
0 5 10 15
Reb
ound number
Number of autoclaving cycles
Mix 23
Appendices 178
Appendix B: Results of concrete durability
B1: Capillary suction of concrete mixes
1‐ The increase in concrete mass with time due to capillary suction
At normal conditions (mixes 1 – 10)
After autoclaving for 15 cycles (mixes 1 – 10)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 1 2 3 4 5
Increase in
concrete mass (kg/m
2)
Square root of time (hours)
Mix 1 Mix 2
Mix 3 Mix 4
Mix 5 Mix 6
Mix 7 Mix 8
Mix 9 Mix 10
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 1 2 3 4 5
Incraese in
mass per unit area (kg/m
2)
Square root of time (hours)
Mix 1 Mix 2
Mix 3 Mix 4
Mix 5 Mix 6
Mix 7 Mix 8
Mix 9 Mix 10
Appendices 179
At normal conditions (mixes 11 ‐ 23)
After autoclaving for 15 cycles (mixes 11 – 23)
0
0.5
1
1.5
2
0 1 2 3 4 5
Increase in concreate mass (kg/m
2)
Square root of time (hours)
Mix 11 Mix 12Mix 13 Mix 14Mix 15 Mix 16Mix 17 Mix 18Mix 19 Mix 20Mix 21 Mix 22Mix 23
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
0 1 2 3 4 5
Increase in m
ass per unit area (kg/m
2)
Square root of time (hours)
Mix 11 Mix 12Mix 13 Mix 14Mix 15 Mix 16Mix 17 Mix 18Mix 19 Mix 20Mix 21 Mix 22Mix 23
Appendi
2‐ Wat
15 cy
Absorption coefficien
t (kg/m
2hr0
.5)
Absorption coefficien
t (kg/m
2hr0
.5)
ices
er absorptio
ycles at age
0
0.1
0.2
0.3
0.4
Mix 1
0
0.1
0.2
0.3
0.4
0.5
0.6
Mix 11
Absorption coefficient
(kg/m
2hr0
.5)
on coefficien
of 91 days
Mix 2
1 Mix 12
0
0.04
0.08
0.12
0.16
0.2
(kg/m
2hr0
.5)
nt of concre
Mix 3 Mix
Mix 13
Mix 20
ete mixes at
x 4 Mix 5
Mix 14 Mix
Mix 21
normal con
Mix 6 M
x 15 Mix 16
Mix 22
ditions and
Mix 7 Mix
6 Mix 17
Mix 23
Norm
15 cy
after autoc
8 Mix 9
Normal
Mix 18
N
1
3
mal
cles
180
laving for
Mix 10
15 cycles
Mix 19
Normal
15 cycles
Appendices 181
Appendix C: Thermogravimetric analysis of cement pastes at normal conditions and after
autoclaving for 50 cycles at the age of 91 days
74767880828486889092949698
100
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (°C)
NormalAutoclaved
82
84
86
88
90
92
94
96
98
100
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (° c)
NormalAutoclaved
80828486889092949698100102
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (°C)
NormalAutoclaved
82
84
86
88
90
92
94
96
98
100
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (°C)
Normal
Autoclaved
82
84
86
88
90
92
94
96
98
100
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (° C)
Normal
Autoclaved
82
84
86
88
90
92
94
96
98
100
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (° C)
Normal
Autoclaved
767880828486889092949698100102
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (° C)
Normal
Autoclaved
70
75
80
85
90
95
100
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (°C)
NormalAutoclaved
84
86
88
90
92
94
96
98
100
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (°C)
Normal
Autoclaved
86
88
90
92
94
96
98
100
0 100 200 300 400 500 600 700 800 900
wgt %
Temperature (°C)
Normal
Autoclaved
CEM I CEM III/B
Mix 1 Mix 2
Mix 5
Mix 18
Mix 7
Mix 19
Mix 21 Mix 23
Appendi
Append
ices
dix D: SEM fo
Normal
Normal
Normal
or cement p
pastes at no
ormal cond
Mix 5
Auto
Mix 11
Auto
Mix 14
Auto
itions and a
oclaved
oclaved
oclaved
after autoclaving for 50
182
0 cycles
Appendi
Append
ices
dix E: Rene LLCPC calculaations of th
e dry mixtuures porositty
183