## 3 Tests Results and Discussion
### Crack Healing of the Pull-Out Specimens  
After the pull-out specimens were exposed to high temperatures, the cracks on their surfaces were observed at different self-healing ages. In terms of exposure to 300 \({}^{\circ}\)C, obvious crystal precipitations began to appear on both sides of the cracks in Group C after 7 days of self-healing, as shown in Figure 17. These precipitates were confirmed to be calcium carbonate (CaCO\({}_{3}\)) in Section 3.4. In addition, the distribution of CaCO\({}_{3}\) crystal particles was visible on the surface around the crack. In contrast, only sporadic CaCO\({}_{3}\) particles appeared in the cracks in Groups A and B. The crystallization of Group C reached its peak on the 14 th day of the self-healing age. The interior of the cracks was more or less filled with CaCO\({}_{3}\) crystals and tended to gradually expand outward. However, for Groups A and B, there was no significant difference from the situation at the self-healing age of seven days. Then, at the self-healing age of 21 days, it was found that  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Group**} & \multirow{2}{*}{**Unhealed**} & \multicolumn{2}{c}{**Residual BS (MPa)**} & \multicolumn{2}{c}{**Relative BS Ratio**} \\ \cline{3-6}  & & **28 Days of** & **90 Days of** & **28 Days of** & **90 Days of** \\  & & **Self-Healing** & **Self-Healing** & **Self-Healing** & **Self-Healing** \\ \hline Group A & 27.35 (0.68) & 28.82 (0.55) & 29.99 (1.19) & 1.05 & 1.10 \\ Group B & 27.07 (1.14) & 28.36 (2.23) & 30.37 (0.63) & 1.05 & 1.12 \\ Group C & 27.41 (0.69) & 28.64 (0.32) & 31.08 (0.72) & 1.05 & 1.13 \\ \hline \hline \end{tabular} Note: BS: bond strength.  
\end{table}
Table 6: Residual BS and relative BS ratios of the healed LWAC after exposure to a temperature of 300 \({}^{\circ}\)C.  
Figure 16: Secondary relative BS ratio of the healed specimens after they were exposed to 300 \({}^{\circ}\)C and damaged in the first pull-out test.  
the concrete surface of Group C exhibited some peeling of the surface. This may be due to the long-term soaking in the curing solution causing some slight erosion damage to the concrete surface. However, when the healing time was extended to 28 days, CaCO\({}_{3}\) crystal crystallization again occurred on the surface of Group C. It is speculated that, as the age increased, the CaCO\({}_{3}\) crystals continued to penetrate deep into the interior of the specimen to crystallize, causing tension damage near the surface and falling off. This inference could reasonably explain the results of the pull-out test of Group C, which showed better strength performance with increasing age. Furthermore, more granular crystal accumulation can be seen in the cracks of Groups A and B. Although the deposition rate was slower, there was still a continuous reaction. In terms of exposure to 500 \({}^{\circ}\)C, as the self-healing age increased, the CaCO\({}_{3}\) crystals in Groups A and B were not obvious, with only quite sparse granular crystals. In comparison, Group C showed crystallization at the self-healing age of seven days. However, compared with the situation at 300 \({}^{\circ}\)C, the crystals were fine and localized. On the 14 th day of self-healing, the healing of Group C was more obvious and began to develop widely outward. There was a better repair trend at the self-healing ages of 21 and 28 days, but there was still some surface peeling on the concrete surface.