Recent progress in understanding setting and hardening of alkali-activated slag (AAS) materials

Alkali-activated slag (AAS with type of slag being blast-furnace slag) binders possesses substantially different hydration mechanisms from Portland cement (PC) binders, leading to distinct setting and hardening behavior. Due to the highly amorphous nature of both of raw materials and hydration products , the characterization of hydrate assemblages and microstructural development of AAS materials is challenging. In the past decades, there has been increasing investigation interests in disclosing the nature of aluminum and sodium containing calcium silicate hydrate gel with undefined stoichiometry (C-(N-)A-S-H) along with the existence of intimately intermixed secondary phases. This paper provides an overview on the recent research progress and understanding of the complex alkali-activation reaction process from the perspectives of hydration kinetics , products and microstructure development . This is critical to the interpretation and control of setting and hardening of AAS materials at the early age. In addition, based on available information, hydration mechanisms of different AAS binders are proposed. For such a complex system, thermodynamic modelling and molecular dynamic modelling have shown their power to correlate the microstructure development and the macroscale behavior of AAS materials, which are discussed in this paper.