The effect of fly ash on controlling alkali-silica reaction (ASR) in simulated alkali solution was studied. The expansion of mortar bars and the content of Ca(OH)2 in cement paste cured at 80 ℃ for 91 d were measured. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were employed to study the microstructure of C-S-H. TEM/energy dispersive spectroscopy (EDS) was then used to determine the composition of C-S-H. The pore structure of the paste was analyzed by mercury intrusion porosimetry (MIP). The results show that the contents of fly ash of 30% and 45% can well inhibit ASR. And the content of Ca(OH)2 decreases with the increase of fly ash. That fly ash reacted with Ca(OH)2 to produce C-S-H with a low Ca/Si molar ratio could bind more Na+ and K+ ions, and produce a reduction in the amount of soluble alkali available for ASR. At the same time, the C-S-H produced by pozzolanic reaction converted large pores to smaller ones (gel pores smaller than 10 nm) to densify the pore structure. Perhaps that could inhibit alkali transport to aggregate for ASR.
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