Self-healing behavior and synergistic mechanisms of cementitious mortars incorporating dual-wall multi-component capsules

The limited intrinsic self-healing capacity of cementitious materials severely restricts the long-term structural durability and resilience. To overcome this challenge, a novel organic-inorganic hybrid capsule was designed and fabricated, featuring a multi-component core of superabsorbent polymers (SAP), a composite expansive agent, and silica fume, encased in a double-layered shell of geopolymer and sand. The influence of SAP particle size (140 μm and 250 μm) and core-to-shell ratio (10:4 and 10:5) on the mechanical and self-healing performance of mortar was systematically examined. Results demonstrated that mortar incorporating capsules with 140 μm SAP and a core-to-shell ratio of 10:5 maintained its mechanical integrity, showing a 28-day compressive strength comparable to the reference mixture. The maximum healable crack width reached 300 μm at 7 days, and the relative penetration resistance index achieved 101% at 56 days, compared to 76.8% for the reference group. Microscopic analysis suggests that this excellent self-healing performance originates from a proposed sequential synergistic effect of water absorption, mineral crystallization, and gel formation. Based on the healed microstructural characteristics, it is deduced that the rapid swelling of SAP provides instantaneous physical crack sealing and establishes a localized moisture transport network. Subsequently, the hydration of the expansive agent generates crystalline phases such as ettringite, brucite, and calcite, forming a rigid healing framework. In the final stage, the pozzolanic reaction of silica fume generates additional C-S-H gel, which further densifies the healed interface and consolidates the repaired microstructure. This study proposes an innovative multi-stage synergistic strategy, offering new insights for developing high-performance and reliable autonomous self-healing cement-based materials. © 2026 Elsevier Ltd