Thermal Degradation Mechanisms and Residual Performance of LS-GGBS-FA–Based Alkali-Activated Recycled Concrete after Exposure to Elevated Temperatures

Alkali-activated recycled concrete (AARC) is an environmentally sustainable building material known for its low energy consumption. By incorporating lithium slag (LS) with highly reactive aluminosilicate materials, the environmental issues related to LS disposal can be effectively mitigated while enhancing AARC performance. Microscopic analysis in this study revealed phase transitions in AARC at high temperatures, resulting in pore and crack expansion, mass loss, and degradation of mechanical properties. The simplex centroid method was employed to investigate the effects of LS, ground granulated blast furnace slag (GGBS), and fly ash (FA) on the mechanical properties of alkali-activated concrete (AAC) after exposure to elevated temperature. The mechanical properties were consistently superior within the LS content range of 5% to 10%, slag content between 85% and 95%, and fly ash content between 5% and 10% after exposure to elevated temperatures. This study also examined the influence of the replacement ratio of recycled coarse aggregate (RCA) on AARC mechanical properties. Mathematical models were developed to characterize the variation in mechanical properties with temperature, facilitating accurate predictions of material behavior after exposure to elevated temperature. Additionally, changes in elastic modulus, peak stress, peak strain, and the stress–strain curve of LS-GGBS-FA AARC before and after exposure to elevated temperatures were examined.