## 3 Results and Discussion
### Compressive Strength Recovery Rate  
Table 8 shows the compressive strength of the mortar after 28 days of standard curing. The compressive strengths of CCM0, CCM1 and CCM2 were 31.2 MPa, 40.6 MPa and 35.5 MPa, respectively. Compared with CCM0, the compressive strengths of CCM1 and CCM2 increased by 30.1% and 13.8%, respectively, indicating that an appropriate dosage of microcapsules can significantly improve the compressive strength of the mortar. This is due to the fact that the microcapsules can fill internal pores of the mortar and thus improve the compressive strength of the mortar [29]. The compressive strength of CCM1 was higher than that of CCM2 because the particle size of WM1 was smaller than that of WM2, which can better fill the internal pores of the mortar and reduce the microdefects inside the mortar [30].  
Figure 8 depicts the compressive strength recovery rate of the mortar as the self-healing time increases. It can be found that the compressive strength recovery rate of CCM0 did not change with increasing self-healing time, a phenomenon that indicates that the intrinsic self-healing ability of cement-based materials is unable to self-heal the pre-damaged CCM0 after 14 days.  
It can be seen from Figure 8 that the compressive strength recovery rates of CCM1 and CCM2 were significantly higher compared with CCM0. The compressive strength recovery rates of CCM1 and CCM2 rose gently during the self-healing time of 1-4 days, while they increased rapidly during the self-healing time of 4-7 days and remained basically constant for 7-14 days, which indicates that the self-healing process of microcapsules on pre-damaged mortar was completed after 14 days. This is because microcracks appear in  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Mortars 1** & **Compressive Strength (after 28 Days of Standard Curing)** \\ \hline CCM0 1 & 31.2 MPa \\ CCM1 1 & 40.6 MPa \\ CCM2 1 & 35.5 MPa \\ \hline \hline \end{tabular} \({}^{*}\)CCM0: control mortar; \({}^{*}\)CCM1: the mortar containing WM1; \({}^{*}\)CCM2: the mortar containing WM2.  
\end{table}
Table 8: Compressive strength of mortars.  
Figure 7: Force-displacement curves of microcapsules.  
the mortar after being pre-loaded, and the stresses at the tips of these cracks can rupture the shell of the microcapsules. The E-44 epoxy resin is released from the microcapsules and flows into the microcracks, where it comes into contact with the 2-ethyl-4-methylimidazole pre-mixed in the mortar to produce curing products that self-heal the microcracks. Figure 9 shows the chemical reaction process of E-44 epoxy resin and 2-ethyl-4-methylimidazole.  
After 14 days of self-healing, the compressive strength recovery rates of CCM0, CCM1 and CCM2 were 54.3%, 83.9% and 90.1%, respectively. Compared with CCM0, the compressive strength recovery rates of CCM1 and CCM2 increased by 54.5% and 65.9%, respectively. The results indicate that WM2 has better self-healing ability for pre-damaged mortar. This is mainly due to the higher initial core content and better compactness of WM2 than WM1 (the microcapsules used in the self-healing experiments were prepared 60 days in advance), which ensured that the self-healing mortar had more healing agent, resulting in a higher compressive strength recovery rate for CCM2 than CCM1. In addition, the micromechanical properties of WM2 were better than WM1, which reduced the risk of rupture during mortar  
Figure 8: Compressive strength recovery rates of mortars.  
Figure 9: Curing process of E-44 epoxy resin and 2-ethyl-4-methylimidazole.  
mixing, and the E-44 epoxy resin was not lost due to microcapsule damage during mortar preparation, thus improving the self-healing ability of the pre-damaged mortar.