Fire resistance of fly ash–ladle slag based geopolymer: Insights on recrystallization of waste glass at high temperature

Improving the fire resistance of alkali-activated blend systems remains a challenge. This study investigates the use of waste glass (WG) to strengthen the high–temperature performance of a class F fly ash (FA)–ladle slag (LS) hybrid system through its recrystallization at elevated temperatures. The results indicate that the moderate incorporation of WG enhances the fire resistance of the pastes. The sample containing 20% WG exhibits the highest strength retention ratio at 800 °C, reaching 2.57 times that at ambient temperature. As temperature rises, the incorporation of WG promotes the formation of Ca-enriched gel products by releasing additional Ca and facilitates the development of crystalline phases through the recrystallization of gel products and unreacted WG, thus enhancing the residual strength. Meanwhile, elevated temperatures accelerate crack propagation and pore coarsening, whereas microcracks and micropores are healed by the melted unreacted WG and viscous sintering of geopolymer. Overall, this study provides in-depth insights into the strength evolution mechanism induced by WG at elevated temperatures, contributing to the potential application of WG for fire resistant geopolymer.