Internal curing and its application to alkali-activated materials: A literature review

Alkali-activated materials (AAM) are considered as promising alternative to Portland cement, as they can utilize industrial by-products or wastes as precursors and contribute to reducing CO2 emissions. However, poor volume stability, especially in the case of alkali-activated slag (AAS) systems, remains a significant obstacle in their large-scale application. In recent years, internal curing has gained increasing attention and has been introduced into the AAM system. This review paper provides an overview of the mechanism of internal curing, common internal curing agents, with a particular focus on the most promising agent—superabsorbent polymers. It also explores the limitations associated with the AAM systems and the advancements made in the internal curing technique within AAM systems. The introduction of voids by internal curing agents typically has a negative impact on mechanical properties. However, this can be (partially) counteracted by the continuous water release during internal curing which promotes hydration. While the effect of internal curing in reducing autogenous shrinkage of AAM systems has been well-established, the effect on drying shrinkage described in different studies varies widely, with some articles even suggesting a negative impact.