Green Preparation of Force-Sensitive Micro-Capsules and Their Application in Self-Healing of Cement Sheath

Micro-capsule has been considered the most promising self-healing material, while the complex and high temperature polymerization process, and environmental unfriendly raw materials limits its wide application. Herein, the green micro-capsule composed of epoxy resin and calcium alginate were prepared at room temperature via needle drop method，O/W/O emulsion method and spraying method. The effects of preparation methods on the water absorption, encapsulation rate of micro-capsules were revealed, and the differences in the self-healing efficiency of cement containing these green micro-capsules were also studied. Among all samples, the micro-capsules prepared by O/W/O emulsion method (MCE-2) owned the highest water absorption 54.71% and the highest epoxy resin content 48.1%. Compared with the blank samples, adding micro-capsules improved the liquidity of cement slurry and facilitated the hydration process, related to the release of extra water. While, the micro-capsules caused additional defects in the cement matrix and weakened the compressive strength of cement. In the self-healing measurement, the composites with MCE-2 showed the biggest mass transfer pressure and least permeability before and after repair. The higher water absorption of MCE-2 significantly increased greater mass transfer resistance to block the erosion of external fluids before repair, and the higher epoxy resin content could ensure stronger sealing effect after repair, achieving the best self-healing performance.