Mechanical performance and impermeability of self-healing concrete for deep mine shaft linings under hydro-mechanical coupling

Concrete structures exposed to severe environments are susceptible to cracking, which accelerates water penetration and durability degradation. Although self-healing technologies have attracted considerable attention, the simultaneous improvement of mechanical recovery and impermeability remains challenging, especially for high-performance concrete applications. In this study, a synergistic self-healing system consisting of modified microcapsules, CaSO₄ whiskers, and catalysts was developed for C70 high-performance concrete used in mine shaft lining applications. Polyurea-based microcapsules containing 1,3-XDI healing agent were synthesized and modified with nano-SiO₂ to enhance capsule stability and healing efficiency. The effects of different nano-SiO₂ contents on microcapsule morphology, encapsulation efficiency, waterproof performance, mechanical recovery, and crack-healing behavior were systematically investigated. The optimized microcapsules exhibited improved shell compactness and dispersion stability. After damage and healing, the optimized concrete achieved compressive, splitting tensile, and flexural strength recovery rates of 97.2%, 93.9%, and 96.0%, respectively. Furthermore, hydro-mechanical coupling tests demonstrated reduced permeability degradation compared with the reference concrete. The enhanced performance was attributed to the synergistic contribution of crack bridging by CaSO₄ whiskers, controlled release of healing agents from microcapsules, and catalyst-assisted polymerization reactions. The proposed strategy provides a promising approach for developing durable self-healing concrete structures under complex service conditions.