Trigger mechanism investigations of microcapsules containing SAC for rapid self-healing mortars

Despite the growing interest in self-healing technologies, the trigger efficiency of microcapsules containing solid particles has not been systematically investigated. Microcapsules incorporating calcium sulphoaluminate cement (SAC) particles were synthesized via a melt-cooling method. The resulting microcapsules exhibit a well-defined core-shell structure with an average diameter of 996.8 ± 28.7 µm, a shell thickness of 60.7 ± 28.4 μm, a core content of 57.4 wt%, and sustained a compressive load of 7.2 ± 0.9 N before failure. Trigger efficiency was significantly enhanced from 23.2 ± 2.5 % to 80.9 ± 5.2 % by optimizing key parameters, including surface modification, matrix strength, hydration duration, and microcapsule shell strength. Environmental durability tests indicated that carbonation, sulfate attack, and freeze-thaw cycles had a negligible impact on trigger efficiency. However, exposure to wet-dry cycles for 28 days reduced the trigger efficiency to 61.1 ± 3.1 %. The underlying trigger mechanism was also investigated through Extended Finite Element (XFEM) analysis, which quantified the correlation between the matrix-to-capsule stiffness ratio and the critical rupture stress. Finally, the self-healing performance of mortars incorporating the SAC microcapsules was evaluated. Cracks below 200 μm were effectively sealed within 24 h. The healing products—primarily CaCO 3 , ettringite, (AFt), and calcium silicate hydrate (C–S–H) gel, possess good impermeability and mechanical strength recovery, confirming the potential of capsules for rapid and efficient self-healing in cementitious systems.