Effects of high temperature and post-fire-curing on compressive strength and microstructure of calcium carbonate whisker-fly ash-cement system

Building fire disasters may cause large economic loss and casualties. To improve the fire resistance ability of concrete and repair the fire-damaged concrete structures using an in-situ repairing technique (such as post-fire-curing) can greatly offset these adverse effects. Thus, the present study employed fly ash (FA) to form a CW-FA-cement system which was proved to enhance the high-temperature resistance of cement and CW blended cement and was also favorable for recovery of compressive strength and microstructure induced by water re-curing. In details, incorporation of FA was effective to reduce the deterioration of cement and CW blended cement and was favorable for recovery of compressive strength and microstructure after water re-curing. Incorporation of CW was favorable to increase the restorability of compressive strength re-cured after 400 °C and performed a combined effect with FA to improve the recovery of compressive strength re-cured after 800 °C. Through the microstructural tests, the deterioration of compressive strength was due to the decomposition of hydration products. The recovery of compressive strength was due to the rehydration of dehydrated cement, further hydration of unhydrated cement particles, pozzolanic effect of FA and combined effect of CW and FA. Furthermore, the cement blends containing CW and FA had a good high temperature resistance and restorability.