Enhancing internal curing of alkali-activated slag mortar through activator pre-soaking of lightweight aggregates

This study proposes a novel strategy in which lightweight aggregates (LWAs) are pre-soaked in the alkaline activator, enabling them to function simultaneously as internal curing reservoir and reactive participants in alkali-activated slag (AAS) mortar. Owing to the improved chemical compatibility between the stored liquid and the surrounding pore solution, activator pre-soaking reduced reaction retardation and promoted a more gradual and sustained liquid release compared with conventional water pre-soaking. Consequently, self-desiccation and the associated autogenous shrinkage were more effectively mitigated. The restrained cracking tendency of AAS mortar was also markedly reduced, accompanied by a transition in the post-peak fracture response from brittle to more ductile behaviour. In addition, the latent reactivity of the LWA was exploited through the release of Si and Al species, which promoted reaction-product formation and densification near the LWA-paste interface. As a result, the lack of measurable 1-day strength observed with water pre-soaking was largely overcome, and the elastic modulus was better preserved. These findings, together with the simplified practical implementation of this method, support activator pre-soaking as a promising preconditioning approach for LWA-incorporated AAS systems.