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RISS 인기검색어
- 검색키워드
- 저자 : Burcu Akcay (검색결과 3 건)
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Aggregate Restraining Effect on Autogenous Shrinkage of Cementitious Materials
Burcu Akcay 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.8
In this paper the restraining effect of aggregates on autogenous shrinkage of cementitious materials is investigated by usingdifferent maximum aggregate sizes. Experimental studies were conducted to determine the restraining effect of aggregates onautogenous shrinkage of composites with a paste to aggregate ratio of 70 to 30 by volume percent. It was shown that the autogenousshrinkage is reduced by addition of aggregate, and this effect can be predicted using Pickett’s expression. A comparison of the resultsof calculated autogenous shrinkage with that of experimental studies on cement paste, mortars, concrete, and also individualcomposites containing cement paste and different particle size of aggregate is presented. The use of the modulus of elasticity obtainedfrom the meso-mechanical modeling gave satisfactory predictions in calculating the autogenous shrinkage of cementitious materials. The microstructural characteristics of samples were identified using their pore size distributions that were determined by mercuryintrusion porosimetry tests. The results show that experimental and predicted values of autogenous shrinkage are in good agreements.
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Burcu Akcay,Mehmet Ali Tasdemir 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.11
In the literature, there are some conflicting results regarding the influence of metakaolin (MK) addition on autogenous shrinkage behavior of cementitious materials. In this study, with the aim of identifying how the use of MK changes the properties of cementitious materials, cement was partially replaced by MK in different proportions (8%, 16%, and 24%) in pastes produced with variable water/binder ratios (w/b; 0.28, 0.35 and 0.42). The temperature development and calcium hydroxide consumption by thermogravimetric analysis were observed to better characterize the effects of MK on the autogenous shrinkage behavior. The mechanical properties such as compressive strength and flexural strength were experimentally investigated. The results show that the addition of MK has contrasting effects on autogenous shrinkage during early ages depending on the w/b ratio. Thermogravimetric analysis showed that the amount of stratlingite was smaller in pastes with low w/b ratios than in pastes with high w/b ratio. The calcium hydroxide consumption with the pozzolanic reaction of MK was significant even at 2 days, but consumption ratios with respect to the reference paste slowed down at 7 to 28 days.
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Fracture behavior and pore structure of concrete with metakaolin
Akcay, Burcu,Sengul, Cengiz,Tasdemir, Mehmet ali Techno-Press 2016 Advances in concrete construction Vol.4 No.2
Metakaolin, a dehydroxylated product of the mineral kaolinite, is one of the most valuable admixtures for high-performance concrete applications, including constructing reinforced concrete bridges and impact- and fire-resistant structures. Concretes produced using metakaolin become more homogeneous and denser compared to normal-strength concrete. Yet, these changes cause a change of volume throughout hardening, and increase the brittleness of hardened concrete significantly. In order to examine how the use of metakaolin affects the fracture and mechanical behavior of high-performance concrete we produced concretes using a range of water to binder ratio (0.42, 0.35 and 0.28) at three different weight fractions of metakaolin replacement (8%, 16% and 24%). The results showed that the rigidity of concretes increased with using 8% and 16% metakaolin, while it decreased in all series with 24% of metakaolin replacement. Similar effect has also been observed for other mechanical properties. While the peak loads in load-displacement curves of concretes decreased significantly with increasing water to binder ratio, this effect have been found to be diminished by using metakaolin. Pore structure analysis through mercury intrusion porosimetry test showed that the addition of metakaolin decreased the critical pore size of paste phases of concrete, and increasing the amount of metakaolin reduced the total porosity for the specimens with low water to binder ratios in particular. To determine the optimal values of water to binder ratio and metakaolin content in producing high-strength and high-performance concrete we applied a multi-objective optimization, where several responses were simultaneously assessed to find the best solution for each parameter.
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