A comprehensive review on self-healing cementitious composites with crystalline admixtures: Design, performance and application

Crystalline admixture (CA) has garnered attention as a promising self-healing agent for cementitious composites. This paper aims to provide a compressive review on the effects of CA on the self-healing behaviours and durability properties of cementitious composites. CA is in powder form, consisting of Portland cement and special chemicals as self-healing stimulants. Since the powder-form CA was directly mixed with the cementitious mixture, CA addition has no significant impact on the properties of fresh concrete but enhances the compressive strength of CA-cementitious composites. Furthermore, self-healing is activated by moisture, resulting in the production of calcium-based self-healing products. In terms of crack closure efficacy, CA-cementitious specimens cured under wet/dry cycle demonstrated a higher crack closure ratio than those cured under water immersion or air exposure. Specimens cured in chloride solution exhibited the best healing recovery. However, reduced mechanical recoveries are observed in specimens exposed to freeze-thaw cycles and those in chloride solution, while better mechanical recoveries are found in specimens exposed to wet/dry cycles. Overall, CA can reduce the sorptivity, permeability, chloride penetration, and the depth of sodium ions penetration, offering favourable protection for cementitious composites. Although some durability properties of CA-cementitious composites have been explored, further studies are required to investigate potential effects on shrinkage, ingress of aggressive ions, carbonation, and alkali-silica reaction (ASR). The application of CA in cementitious composites could be considered as a cost-effective approach for inducing self-healing capability, given its affordable and straight-forward construction process.