High temperature resistance of fly ash/GGBFS-based geopolymer mortar with load-induced damage

This study investigated the effect of elevated temperatures on the residual mechanical behaviors of geopolymer mortars with initial damage induced by mechanical load. Geopolymer mortar was prepared using different fly ash/ ground granulated blast furnace slag (GGBFS) ratios and was activated by sodium silicate and sodium hydroxide solution. The physical properties and residual mechanical strength were investigated and compared with those of Portland cement mortar (PCM). After elevated temperature exposure, microstructure of GSM was studied by various microcharacterizations. The results show that before the exposure to high temperature, the addition of GGBFS increased the compressive strength of GSM, but made it more sensitive to the preloading damage, leading to the increased strength loss. After exposed to combined preloading damage and high temperature exposure, the GSM exhibited lower residual strength than the ones only suffered from preloading damage or high temperature exposure. Compared to the PCM, GSM with GGBFS performed better at temperature of 300 degrees C, but became worse at temperatures of 500 and 700 degrees C due to severe damage caused by combined high load level and large heat exposure. Finally, a low percentage of GGBFS (less than 20%) can be considered as an optimal amount for the GSM to achieve excellent fire resistance capacity.