The effect of curing regimes on physico-mechanical, microstructural and durability properties of alkali-activated materials: A review

Abstract

Alkali-activated materials (AAMs) refer to a group of alternative materials to ordinary Portland cement concrete with reduced environmental footprint. Despite several benefits of AAMs, due to certain shortcomings such as the variation in mechano-durability properties through the adaptation of different curing regimes, their use in large scale construction has been limited. This tendency, however, can be enhanced through the use of proper curing techniques adopted in accordance with the mixture’s overall materials' ratio and chemical composition. In this regard, the most commonly used curing regimes for AAMs are conducted in thermal or ambient temperature environments, adopted in the form of immersion of the AAMs in water, ambient and high humidity, sealing, oven and, more recently, microwave curing. In that respect, this article aims to review and discuss the recent advances in understanding and optimizing the mechanical, durability and microstructural properties of AAMs in different curing regimes. On this basis, sealing and microwave curing are found to be the most suitable curing regimes used in both one-part and two-part AAMs (especially for high calcium system). The favorable physico-mechanical and microstructural properties of AAMs can be attributed to the enhanced polymerization and avoidance of significant moisture loss in sealing and microwave curing. In contrast, instant immersion in water (water curing) and continued thermal curing is found to be the least favorable curing regime for AAMs due to the dilution of the activator and an increase in free-water within air-void pores, versus that of vaporizing microstructural water content, respectively. At the end, the challenges, solutions and recommendations for future studies on the curing regime of AAMs are provided to discuss the future potentials within this area of research.