Dual-trigger microcapsules for autonomous crack healing in marine concrete: Synergistic response to mechanical stress and chloride ions

To overcome limitations of single-trigger self-healing systems, this study developed microcapsules (MCs) responsive to both mechanical stress and chloride ions for marine concrete repair. Ethyl cellulose/nano-silica shells encapsulating epoxy resin were synthesized via solvent evaporation method, with PbSO 4 embedded for chloride activation. MCs exhibited optimal size (70–120 μm), thermal stability (>190 °C), and homogeneous PbSO 4 distribution. Increasing PbSO 4 content enhanced chloride responsiveness, forming pores that released healing agent via osmotic pressure, while improving MC stiffness. Additionally, the self-healing mortars demonstrate notable strength recovery, with the highest healing rate of 126.30 % under standard curing and 114.50 % under seawater curing, reflecting the MCs' robust performance in aggressive environments. Cracks up to 229.7 μm width were effectively healed within 7 days, with healing efficiency positively correlating with PbSO 4 content. The porosity reduction rate rose with the increase in PbSO4 dosage, reducing porosity by 9.42 %–26.71 % post-healing. Additionally, MC significantly enhanced the chloride ion permeability resistance of self-healing mortars, achieving a reduction rate of 67.37 %–84.90 %. This d ual-trigger system provides targeted, efficient self-healing for marine concrete infrastructure, significantly enhancing durability.