Synergistic swelling-curing self-healing in cementitious materials via KH570-modified nano-silica enhanced epoxy/alginate microcapsule

Cementitious materials are prone to cracking under environmental variations and external loads, and microcapsule-based self-healing approach provides an effective solution. Calcium alginate microcapsule is a promising eco-friendly system for self-healing cementitious materials but may face challenges regarding core leakage and interfacial incompatibility, while the underlying self-healing mechanism still remains unclear. To address these limitations, this study developed a novel epoxy/calcium alginate microcapsule enhanced with KH570-modified nano-silica. The physicochemical properties, self-healing efficiency, and interfacial mechanisms were systematically investigated through experimental characterization and molecular dynamics simulations. It is shown that increasing the core/shell ratio from 4:1 to 6:1 significantly elevated the epoxy content from 63.77% to 85.24%. The incorporation of KH570-modified nano-silica successfully improved shell structure and surface hydrophobicity with contact angle increasing from 47.7° to 101.3°, which effectively reduced the 28d core loss proportion from 28.65% to 8.69%. Furthermore, it functioned as a coupling bridge, enhancing the organic-inorganic compatibility through mechanical interlocking and interfacial interactions. The mortar specimens containing the modified microcapsules achieved a remarkable compressive strength recovery of 145.53%, a water permeability reduction rate of 99.87% and an ultrasonic velocity recovery ratio of 41.23%. Molecular dynamics simulations provided atomic-level evidence for the multi-step cross-linking of epoxy, confirming the cross-linking latency and highlighting the critical role of early-stage swelling of calcium alginate shell. This work elucidates the synergistic self-healing mechanism of alginate microcapsule, demonstrating that the KH570-modified nano-silica enhanced microcapsules significantly improve crack closure and mechanical restoration in cementitious materials.