Mechanical Properties of Mechanical Properties of HPC withHPC with
Expansive Additive andExpansive Additive andShrinkage Reducing Shrinkage Reducing
Admixture under Simulated Admixture under Simulated Completely-Restrained Completely-Restrained Condition at Early AgeCondition at Early Age
Takafumi NoguchiTakafumi Noguchi The University of The University of Tokyo, JapanTokyo, JapanPark Sun-GyuPark Sun-Gyu Yonsei University, KoreaYonsei University, KoreaIppei MaruyamaIppei Maruyama Hiroshima Hiroshima University, JapanUniversity, Japan
BackgroundBackground High-performance Concrete (Low W/C)High-performance Concrete (Low W/C)
Self-desiccationSelf-desiccationAutogenous ShrinkageAutogenous Shrinkage
Under Restraint ConditionUnder Restraint Condition CrackingCracking
Influence on Durability & AestheticInfluence on Durability & Aesthetic Use ofUse of
Expansive AdditionExpansive Addition Shrinkage Reducing AdmixtureShrinkage Reducing Admixture
Objective of StudyObjective of Study Behaviour of Early Age HPC with and Behaviour of Early Age HPC with and
withoutwithout Expansive AdditionExpansive Addition Shrinkage Reducing AdmixtureShrinkage Reducing Admixture
Restraint Free ConditionRestraint Free Condition Shrinkage StrainShrinkage Strain
Under Restraint ConditionUnder Restraint Condition Strain & StressStrain & Stress Creep BehaviourCreep Behaviour
Control of Autogenous Shrinkage Cracking Control of Autogenous Shrinkage Cracking
Variable Restraint Testing Variable Restraint Testing Machine Machine Fresh concrete is cast into the framework of the testing machine.
Specimen size is 1500 mm in length and 100 mm x 100 mm in cross sectional area
The ends of specimen are fixed to the cross-head, which is fixed to the frame, by claws which hold the concrete specimen and are able to exert tensile or compressive force.
The load through the specimen is monitored by a load cell with accuracy of 1 N.
The longitudinal deformation of concrete specimen is monitored by four LVDTs with accuracy of 0.125 μm.
Experiment is commenced after the concrete setting.
Program Flow of Simulated Program Flow of Simulated Completely-Restrained TestCompletely-Restrained Test
Completely restrained condition is simulated by maintaining the total deformation of the specimen within a threshold, which is defined as the permissible change in the length of the specimen.
There are two controlling triggers.
One is stressstress trigger. Another is strainstrain
trigger.
While repeating this process in VRTM,a completely-restrained condition is achieved andthe stress generated by shrinkage is measured.
Mix Proportions of Mix Proportions of ConcreteConcrete
CompositionComposition NHCNHC EHCEHC SHCSHC
Cement (kg/mCement (kg/m33)) 550550 530530 550550
Expansive additive (kg/mExpansive additive (kg/m33)) 00 2020 00
Shrinkage reducing admixture (kg/mShrinkage reducing admixture (kg/m33)) 00 00 66
Water (kg/mWater (kg/m33)) 165165 165165 165165
Fine aggregate (kg/mFine aggregate (kg/m33)) 781781 781781 781781
CoarseCoarse aggregate (kg/m aggregate (kg/m33)) 869869 869869 869869
High-range water-reducing admixture High-range water-reducing admixture (cement weight %)(cement weight %) 0.70.7 0.70.7 0.70.7
Experiments Experiments Compressive Strength Compressive Strength Tensile StrengthTensile Strength Modulus of ElasticityModulus of Elasticity Free Autogenous ShrinkageFree Autogenous Shrinkage
Sealed with a polyester film at 20 ºCSealed with a polyester film at 20 ºC Stress Development under Simulated Stress Development under Simulated
Completely-RestraintCompletely-Restraint Sealed with a polyester film at 20 ºCSealed with a polyester film at 20 ºC Trigger of stress and strain : 0.01 MPa and Trigger of stress and strain : 0.01 MPa and
2 x 102 x 10-6-6
Mechanical Properties of Mechanical Properties of ConcreteConcrete
Compressive Strength Compressive Strength (MPa)(MPa)
Tensile Strength Tensile Strength (MPa)(MPa)
Modulus of ElasticityModulus of Elasticity (GPa)(GPa)
11dayday
33daysdays
55daysdays
11dayday
33daysdays
55daysdays
11dayday
33daysdays
55daysdays
NHCNHC 25.625.6 56.556.5 65.465.4 2.22.2 4.44.4 4.94.9 22.522.5 30.630.6 32.332.3
EHCEHC 25.125.1 51.451.4 57.757.7 2.42.4 3.63.6 4.14.1 22.622.6 29.729.7 33.133.1
SHCSHC 24.924.9 53.853.8 64.164.1 2.32.3 3.13.1 3.83.8 23.123.1 29.929.9 33.033.0
Autogenous ShrinkageAutogenous Shrinkage
-500
-400
-300
-200
-100
0
0 1 2 3 4 5 6
Age (days)
Auto
geno
us S
hrin
kage
(x10
-6)
NHCEHCSHC
Autogenous shrinkages of NHC and SHC occurres Autogenous shrinkages of NHC and SHC occurres at a rapid rate in the first few hours and the rate at a rapid rate in the first few hours and the rate decreased afterward.decreased afterward.
In EHC, after a few hours expansion In EHC, after a few hours expansion is observed.is observed.
Expansive addition and shrinkage reducing Expansive addition and shrinkage reducing admixture can obviously reduce the admixture can obviously reduce the autogenous shrinkage of HPC.autogenous shrinkage of HPC.
Temperature Histories Temperature Histories
05
1015202530
0 1 2 3 4 5 6
Age(days)
Tem
pera
ture
(ºC)
NHCEHCSHC
Almost constant temperature never causes Almost constant temperature never causes significant expansion.significant expansion.
Strain under Simulated Strain under Simulated Completely-RestraintCompletely-Restraint
-4-3-2-101234
0 1 2 3 4 5 6Age (days)
Strai
n (x1
0-6)
NHCEHCSHC
Deformation is well controlledDeformation is well controlledwithin the range of the threshold within the range of the threshold value, 1value, 1m.m.
Tens
ion
Com
pres
sio
n
Stress under Simulated Stress under Simulated Completely-RestraintCompletely-Restraint
-0.5
0.0
0.5
1.0
1.5
2.0
0 1 2 3 4 5 6Age (days)
Tens
ile S
tress
(MPa
) NHCEHCSHC
Invisible Invisible CrackCrack
Tensile Strength of NHC at 1 day = 2.2 MPa (x 0.7 = 1.54 MTensile Strength of NHC at 1 day = 2.2 MPa (x 0.7 = 1.54 MPa) Pa)
In EHC and In EHC and SHC,SHC,lower tensile lower tensile stress and no stress and no cracking.cracking.
Schematic Diagram for Creep Schematic Diagram for Creep EstimationEstimation
Age
Stra
in
Strain Trigger
AccumulatioAccumulation ofn ofElastic Elastic StrainStrain
Free Free AutogenousAutogenous
ShrinkageShrinkage
Creep Creep StrainStrain
εi,creep = εi,free - εi,elastic
Elastic Strain Elastic Strain measured measured from the recovery from the recovery cycles of VRTMcycles of VRTM
Creep StrainCreep Strain
-400-350-300-250-200-150-100-50
0
0 1 2 3 4 5Age (days)
Cree
p St
rain
(x10
-6)
NHCEHCSHC
Creep is quite significant in the deformation of Creep is quite significant in the deformation of HPC at early age, corresponding to 90 % of the HPC at early age, corresponding to 90 % of the free shrinkage strain.free shrinkage strain.
Creep strain shows the tendency to Creep strain shows the tendency to increase rapidly immediately after the increase rapidly immediately after the setting up to 10 hours.setting up to 10 hours.
A considerable tensile stress in A considerable tensile stress in HPC can be relaxed under HPC can be relaxed under restraint at early age.restraint at early age.
Creep Coefficient in Each Creep Coefficient in Each StepStep
05
1015202530
0 1 2 3 4 5
Age (days)
Cree
p Co
effici
ent NHC
EHCSHC
εi,co-creep = εi,creep / εi,elastic
Creep coefficient of NHC is Creep coefficient of NHC is lower than those of EHC and lower than those of EHC and SHC in the beginning.SHC in the beginning.
0
2
4
6
8
10
0 0.2 0.4 0.6 0.8 1
Age (days)
Cree
p Co
effici
ent NHC
EHCSHC
Tensile stress in restrained EHC and Tensile stress in restrained EHC and SHC is lower than that in NHC at SHC is lower than that in NHC at early age.early age.
Concluding Remarks Concluding Remarks (1st)(1st)
The variable restraint testing machine The variable restraint testing machine can show how tensile stress and strain can show how tensile stress and strain develop under restrained condition in develop under restrained condition in HPC with and without expansive HPC with and without expansive addition and shrinkage reducing addition and shrinkage reducing admixture.admixture.
The tensile stress in HPC with expansive The tensile stress in HPC with expansive addition or shrinkage reducing addition or shrinkage reducing admixture under completely restrained admixture under completely restrained condition at early age was lower than condition at early age was lower than that of normal HPC.that of normal HPC.
Concluding Remarks Concluding Remarks (2nd)(2nd)
Normal HPC shows larger creep Normal HPC shows larger creep strain but smaller creep coefficient strain but smaller creep coefficient than concrete with expansive addition than concrete with expansive addition or shrinkage reducing admixture. or shrinkage reducing admixture. Normal HPC is sensitive to Normal HPC is sensitive to autogenous shrinkage cracking.autogenous shrinkage cracking.
Expansive addition and shrinkage Expansive addition and shrinkage reducing admixture make a crack reducing admixture make a crack prevention effect on HPC at early age.prevention effect on HPC at early age.
