a study on durability of high-performance concrete

2015 營建工程與管理學術研討會

The 19th Symposium on Construction Engineering

and Management—CEM 2015

A study on durability of high-performance

concreteChao-Lung Hwang#1, Andrian H. Limongan#2, Shu-Ti Yang#3, Trong-Phuoc Huynh#4

#Department of Construction and Civil Engineering, National Taiwan University of

Science and Technology, 43 Keelung Rd, Sec. 4, Taipei 10607, Taiwan [email protected]

[email protected]

[email protected]@ctu.edu.vn

Abstract

Paste amount and its proportion in the concrete mixtures play an important role in

creep and shrinkage development. For this reason, a study about the influence of paste

amount on durability of concrete was conducted. Densified mixture design algorithm

(DMDA) was applied in this study to design High performance concrete (HPC) and

was compared with ordinary Portland concrete (OPC). The designed strength for

concrete used in this study was 6,000 Psi at 28-day age. The test results show that HPC

has higher strength than OPC in the long run. Furthermore, the drying shrinkage and

creep results indicated the good durability of HPC.

Keywords: High-performance concrete, Densified mixture design algorithm, Drying

shrinkage, Creep, Durability

1. IntroductionConcrete is undoubtedly one of the most used construction material in the world.

Therefore, it is essential to maintain the quality and performance of concrete. Concrete

structures are designed to last decades, but deformations of concrete that evolve over

time, such as drying concrete and creep, can lead to catastrophic failures [1]. The

development of creep depends on stiffness and coarseness of aggregate, water-to-

cement (w/c) ratio, volume of paste and coarse aggregate, cement type, admixture type,

curing condition, ratio of volume-to-surface area, environmental conditions, magnitude

of loads, and age of loading. However, the creep of concrete is mainly due to the creep

of cement paste, while the aggregate is the only portion that resist against creep [2, 3].

Consequently, the paste amount and its proportion in the mixture play an important role

in creep development.

High-performance concretes (HPC) designed by densified mixture design

algorithm (DMDA) are expected to not only have high strength, but also good durability.




The DMDA technology combines the mixture proportion algorithms of both volume

and weight methods, resulting in a densely packed aggregate with the optimized amount

of cement paste. This method has successfully applied to many projects in Taiwan,

including Taipei 101 and Tuntex Sky Tower, the two tallest building in Taiwan [4, 5].

The addition of pozzolanic materials and water-reducing agent are common in

HPC mix proportion, as they can reduce creep and shrinkage, as well as achieving high

strength and workability [6]. Thus, this research investigates the durability aspect of

HPC designed by DMDA method, compared to ordinary Portland concrete (OPC)

designed by ACI method.

2. Experimental program

2.1. Materials

The type I Portland cement produced by Asia Cement, class-F fly ash (FA)

supplied by Taichung Power Plant, and blast furnace slag (BFS) provided by China Hi-

Ment Corporation are used in this study. Crushed coarse aggregate (CA) (Dmax 19mm,

density 2.69, absorption capacity 1.0%) and natural sand (fineness modulus 3.0, density

2.61, absorption capacity 1.8%) were provided from local quarries. Local tap water was

used as mixing water and type-G superplasticizer was used to achieve the desired

workability. All materials used conform to the related ASTM standards.

2.2. Mixture proportioning

The mixture proportion of HPC in this study was designed by DMDA technology,

meanwhile OPC was designed using traditional ACI method. The DMDA method

focuses on the “least void” condition through the utilization of FA to fill the void

between blended aggregates and cement paste to fill the rest of the void. The utilization

of fly ash, physically acting as filler, will increase the density of concrete as well as

acting as pozzolanic material [7, 8]. The mix proportions for HPC and OPC are listed

in Table. 1.

TABLE 1

Concrete mixture proportions (kg/m3)

Type Cement BFS FA CA Sand Water SP

OPC 500 0 0 975 737 184 1.7

HPC 263 102 92 932 845 158 2.8

2.3.Sample preparations and test programs

All concrete samples are designed to reach the strength of 6,000 psi at 28 days.




Concrete was mixed in a laboratory food mixer. Portland cement, fly ash, and slag were

mixed with water followed by the addition of natural sand and coarse aggregate.

Superplasticizer was added to control workability of fresh concrete.

The cylindrical samples used in this study have a diameter of 100 mm and height

of 200 mm. The samples were de-moulded 24 hours after casting and then cured in

saturated lime water with temperature of 23±3°C. The compressive strength test were

performed at the age of 3, 7, 14, 28, 56, and 91 days in accordance with ASTM C39-

03. The average of experimental results from three identical samples is adopted. The

drying shrinkage and creep tests were conducted daily until 1 week, and the age of 14,

21, 28, and 56 days after cured for 28 days in accordance with ASTM C512-10. The

drying shrinkage and creep test were carried out at temperature of 23±2°C and humidity

of 60±5%. The creep samples were initially loaded to 25% of the 28-day axial

compressive strength of concrete.

3. Results and discussion

3.1. Compressive strength

Compressive strength is one of the most important parameters for evaluating

whether the concrete conforms to the designed strength. The compressive strength of

both OPC and HPC met the target strength of 6,000 Psi in 28 days, as shown in Fig. 1.

However, it can be seen that OPC had higher compressive strength at the early age, but

at the later age the compressive strength of HPC was higher than OPC. This is mainly

due to the relatively slow reaction of pozzolanic reaction of FA and BFS. The addition

of pozzolanic materials is not only helpful to promote the packing density, but also

chemically improves the interface transition zone through pozzolanic reaction.

Therefore compressive strength of HPC designed by DMDA may significantly improve

in the long run [9].

Fig. 1 Compressive strength development of OPC and HPC




3.2. Drying Shrinkage

Fig. 2 shows the test results of drying shrinkage stored at constant temperature of23±2°C and relative humidity of 60±5% for 56 days after being cured in saturated limewater for 28 days after casting. As shown in Fig. 2, at early stage, OPC already hadgreater shrinkage than HPC, however at the latter stage, the difference became larger.The smaller shrinkage in HPC may be partly attributed to the lower amount of water ashydration and pozzolanic reaction used up significant amount of free water [10]. Theslow reaction of pozzolanic material further supports this trend explanation.

Fig. 2 Drying Shrinkage of OPC and HPC

3.3. Creep

The test results for creep at constant stress of 25% of 28-day compressive strengthare given in Fig. 3. Similar to the case of drying shrinkage, the tests for creep wereperformed in a controlled temperature of 23±2°C and relative humidity of 60±5%. FromFig. 3, it is clearly shown that HPC had lower creep than OPC. HPC designed byDMDA can reduce creep around 30%. In the latter age, the reduction remained constant.The reduction of creep could be attributed to a denser pore structure, stronger pastematrix and improved paste aggregate interface of HPC due to the gel formation ofpozzolanic reaction [10].

Fig. 3 Creep of OPC and HPC




4. ConclusionsBased on the experimental results, the following conclusions may be drawn:

1. HPC designed by DMDA method has better compressive strength and

durability, due to the addition of pozzolanic materials, which act as both

fillers and pozzolanic materials.

2. At the latter ages, the difference in drying shrinkage between OPC and HPC

became larger, which was due to the significant amount of free water used in

pozzolanic reaction.

3. DMDA method can reduce concrete creep around 30% and the reduction

remained constant through latter ages.

4. The lower cement paste used in DMDA method resulted in the better

durability properties of concrete.

AcknowledgmentThis research is sponsored by West Coast Expressway Central Region Engineering

Office, Directorate General of Highways, Ministry of Transportation and

Communications. The authors also want to express gratitude to fellows of Construction

Material Research Laboratory at National Taiwan University of Science and

Technology for their assistance on this research.

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a study on durability of high-performance concrete

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