A state-of-the-art review on the setting behaviours of ground granulated blast furnace slag- and metakaolin-based alkali-activated materials

Alkali-activated materials (AAMs) are inorganic cementitious materials that are regarded as potential substitutes for ordinary Portland cement (OPC) due to their better properties and lower carbon footprint. Ground granulated blast furnace slag (GGBFS) and metakaolin (MK) are two typical precursors used for preparing Ca-containing and Ca-free AAMs, respectively, and they show different alkali activation processes and different compositions and properties of the alkali activation products. This review is mainly focused on the progress made in determining the setting behaviours for alkali activation of these two kinds of precursors. The effects of the chemical compositions of the precursors, activators, and retarders on the setting times of the AAMs are presented. The present study includes an extensive discussion of the effects of retarders on the setting times, strengths and workabilities of AAMs. We also discuss the underlying chemical mechanisms of the setting processes and provide advice for controlling the setting behaviours of alkali-activated GGBFS and MK for better application.