High temperature resistance of slag/fly ash-based geopolymer concrete with fully recycled coarse aggregate

To address the growing need for sustainable construction materials, this study explored the potential of fully replacing natural coarse aggregate (NCA) with recycled coarse aggregate (RCA) in geopolymer concrete, aiming to reduce carbon emissions and utilize construction waste effectively. This study focused on the ability of geopolymer recycled aggregate concrete (GRAC) to maintain operability and intact at high temperatures. Physical properties, mechanical properties, and microstructural were analyzed to understand the damage mechanism under high temperatures. The results indicate that the GRAC can withstand the temperature up to 800 ℃, and the residual compressive strength, splitting tensile strength, and bond strength will not decrease significantly below 400 ℃. Compared with geopolymer concrete prepared by NCA, the GRAC exhibits a reduction in compressive strength and bond strength by 25.22 % and 16.16 %, respectively. Moreover, the maximum reduction of splitting tensile strength and flexural strength is 38.28 % and 37.33 %, respectively. Notably, GRAC has the optimum mechanical properties when the RCA replacement rate is 50 %, with the equivalent strength of a specimen without RCA. The crack width between aggregate and mortar in the interface transition zone is the smallest when the RCA replacement rate is 100 %. Based on data analysis, the prediction model for the residual mechanical strength of GRAC is established, and its correlation coefficient is above 0.9. This study highlights the feasibility of GRAC as a sustainable alternative to conventional concrete, particularly in high temperature applications.