High-temperature performance of ambient-cured alkali-activated binder concrete

Owing to their lower carbon footprint and efficient performance compared to portland cement (PC), alkali-activated binders (AAB) show promising potential as an alternative to PC. The present paper investigates the high-temperature performance of AAB concrete through compressive and bond strength tests. Four different AAB concrete mixes with varying proportions of fly ash: slag (100:0, 70:30, 60:40, and 50:50) cured under ambient conditions are exposed to elevated temperatures. The mechanical performance of AAB concrete is corroborated with microstructural changes. The results show that AAB concrete with fly ash: slag ratio of 70:30 exhibits the best mechanical performance after exposure to elevated temperatures. This behaviour is attributed to the growth of new crystalline phases of akermanite and gehlenite as observed from the X-ray diffraction patterns. This study shows that there is an optimum proportion of slag content beyond which the mechanical performance of AAB concrete significantly deteriorates when exposed to elevated temperatures. The failure pattern of AAB concrete during the bond strength test varies with the precursor proportion and the exposure condition.