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.