RESTRAINT OF DEF EXPANSION USING ADDITIVES AND INVESTIGATION OF MICROSTRUCTURAL NATURES OF THE HARDENED PASTE

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  • YOSHIDA Natsuki
    SHIMANE UNIVERSITY, Science of Environmental Systems, Graduate School of Natural Science and Technology（1060, Nishikawatu-cho Matsue-shi Shimane 690-8504, Japan）
  • SHIBUI Yuto
    GENERAL BUILDING RESEARCH CORPORATION OF JAPAN（5-8-1, Fujishirodai, Suita-shi, Osaka 565-0873, Japan）

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  • 混和材によるDEF膨張の抑制とペースト組織の微視的および化学的特徴

Abstract

<p>The effectiveness of using fly ash （FA） and blast furnace slag （BFS） as measures to restrain delayed ettringite formation （DEF） expansion has been reported. In this study, paste specimens using high-early-strength Portland cement （HPC）, FA, and BFS subjected to expansion tests were analyzed to discuss the effect of additives from a microscopic and chemical point of view. Compositional analysis using EPMA mapping data was conducted to visualize the distribution of ettringite （Ett） and monosulfate （Ms） in the paste tissue. In the HPC system exhibiting remarkable DEF expansion, pixels containing Ett were scattered at the boundary between lighter C-S-H and outer C-S-H. This nature is consistent with the hypothesis of the DEF expansion mechanism presented in past studies. In FA system, there was no Ett scattering around lighter C-S-H that might contribute to expansion, and Ms and Ett were observed inside FA particles. It was presumed that the released sulfate ions from lighter C-S-H were consumed by FA particles in the vicinity of the cement particles, and DEF expansion was thought to be suppressed by the additional effect. In the BFS system, Ms was stably formed, and no expansive Ett was found in the microstructure around the lighter C-S-H. It is assumed that reactive Al2O3 in BFS contributes to the stabilization of Ms.</p>

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