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In this study, the strength development and microstructure evolution of alkali-activated fly ash (AAF), granulated blast furnace slag (AAG), and metakaolin (AAM) mortars under standard curing, steam curing, and oven curing conditions were investigated. The results show that 80 °C steam curing was more suitable for AAF mortar. Although oven curing was not as good as steam curing under the same temperature, the water evaporation increased the volume density of the N-A-S-H gel and refined the pore structure. For AAG mortar, the strength developed according to a Boltzmann function with time under steam curing conditions, which increased rapidly in the first 8 h, but grew little after about 15 h. Moreover, the strength development was severely limited by steam curing at 60 °C, and decreased under oven curing conditions due to the formation of microcracks that were induced by temperature stress and chemical shrinkage. For AAM mortar, the strength developed according to an Allometric power function with time under steam curing conditions, and the N-A-S-H gel formed in AAM had a higher polymerization degree and denser structure compared to that in AAF. The compressive strength of AAM mortar was 31.7 MPa after 80 °C steam curing for 4 h, and the standard curing time required to reach the same strength was less than 24 h, indicating that the standard curing was more suitable.
Kong et al. (Thu,) studied this question.