Cracking and chemical composition of cement paste subjected to heating and water re-curing

Abstract

Water re-curing of fire-damaged concrete may reduce the environmental and economic impacts of repair operations by re-using the existing concrete. To clarify the rehydration mechanism, the effects of water re-curing on the microstructure and chemical properties of fire-damaged cement paste were examined. Analysis by X-ray CT showed that heating led to radial cracks that propagated horizontally and vertically in the cement paste specimen. Water supply led to a growth in the cracked space through an increase in the connectivity of the crack network. This growth may be due to expansion caused by the rehydration of CaO into Ca(OH)2. Chemical analyses suggest that the rehydration reaction differs from the initial hydration in that C2S plays a greater role in generating C-S-H gel during the earlier period of water re-curing.