Mechanical behavior and microstructural performance of geopolymer recycled mortar incorporating CNTs and GO under elevated temperatures

The utilization of geopolymer recycled mortar (GPRM) could be an economical and sustainable solution for the construction industry. While GPRM exhibits excellent mechanical properties (MP) at ambient temperature, its MP after high-temperature exposure remains unclear. In this study, twelve groups of GPRM samples with different mix proportions were designed with recycled aggregate replacement ratio (ARR) (0%, 50%, 100%), temperatures (25°C, 200°C, 400°C, 600°C,), Carbon nanotubes(CNTs) content (0.1%), and graphene oxide(GO) content (0.005%, 0.01%) as the main parameters. The variation patterns of GPRM compressive strength (CS) after high-temperature exposure were investigated through mechanical property (MP) tests after heating, and the influence of nanomaterials CNTs and GO incorporation on the internal injury development of GPRM after high-temperature exposure was revealed through microscopic tests. The results showed that as the recycled ARR rose from 0% to 50% and 100%, the CS after 600°C decreased by 11.34% and 26.5%, respectively. When the CNTs content was 0.1%, the CS after 600°C was enhanced by 15.16% compared to GPRM without nanomaterials (CNTs and GO). When GO content was 0.005% and 0.01%, the CS after 600°C was enhanced by 23.95% and 35.92%, respectively. Microscopic test results indicated that the phase composition of GPRM after high-temperature exposure was basically similar to that under ambient temperature conditions. The addition of nanomaterials CNTs and GO significantly improved the internal structural consistency and homogeneity of GPRM after high-temperature exposure, making crack generation more regular and orderly.