Comprehensive study of moist curing duration and activator type on mechanical properties, shrinkage, and cracking of alkali-activated slag

Abstract

Despite the considerable research efforts, shrinkage and cracking of alkali-activated slag (AAS) is still a delicate issue. One of the reasons is the enormous complexity of these materials, which originates from different activators, their different dosing, and different approaches for curing. Therefore, the effect of the duration of moist curing of AAS pastes with the three most common sodium activator types (hydroxide, waterglass, carbonate) of the same molarity 4M Na+) and the same starting slag volume fraction (0.52) on their mechanical properties, shrinkage, and cracking performance was complexly investigated throughout one year. Shrinkage was assessed manually by measuring length changes and automatically using embedded strain gauges. A non-destructive resonance method was newly applied to monitor the evolution of cracking over time, including the physical closure of cracks. The obtained results emphasise the fundamental role of an activator for curing effectiveness based on the rate of reaction and microstructural refinement.