Application of alginate-based epoxy microcapsule in self-healing concrete

During the service life of concrete structures, microcracks are prone to occur, leading to strength degradation and reduced durability. Traditional repair methods rely on manual intervention and are unable to promptly detect and repair cracks. In this study, a novel alginate-based microcapsule was developed, consisting of calcium alginate as the shell and epoxy as the core, to enable autonomous crack healing in concrete. This system allows the capsules to rupture upon crack formation and release the core material to initiate the healing reaction. Experimental results demonstrated that microcapsules possessed a spherical morphology and excellent thermal stability. The core content reached 84.39% before immersion and remained at 72.12% after 1 day in cement filtrate, indicating outstanding core retention capacity. Mortar specimens containing 5 wt% microcapsules achieved a compressive strength recovery rate of up to 145.4% after 7 days of self-healing, as the ruptured microcapsules released epoxy and formed dense interfacial networks within crack regions. Molecular dynamics simulation was employed to investigate the reaction process between epoxy and curing agent, revealing the stepwise network formation during crosslinking. The results confirmed the feasibility and remarkable self-healing performance of the alginate-based epoxy microcapsule system, providing a sustainable and cost-effective approach to enhancing structural durability.