## 3 Tests Results and Discussion
### Results of the Pull-Out Test
#### 3.2.1 Local Bond-Slip Relationship and Bond Strength of LWAC at Room Temperature
As mentioned above, for rebar with short bonded anchor lengths, good restraint, and adequate cover, the pull-out specimen should exhibit rebar pull-out failure. After being exposed to high temperatures, the concrete specimens suffered some degree of heat damage. Regardless of the control group or the experimental group, the pullout test showed rebar pull-out failure. Figure 6: The \(\tau\)–s curve of each group of specimens at room temperature. Figure 7: Bond strength of LWAC at room temperature. As mentioned previously, thermocouples 1 and 2 were embedded inside the pull-out specimens, as shown in Figure 4. Under different target temperatures, the relationship between the internal concrete temperature and the heating time of each group of specimens was roughly the same. Therefore, only the results of certain specimens were selected as representatives. Figure 8 shows the results of a single measurement. In the case of a target temperature of 300 \({}^{\circ}\)C, the maximum temperatures of the two thermocouples were approximately 98.2 \({}^{\circ}\)C and 90.8 \({}^{\circ}\)C, respectively, as shown in Figure 8a. In the case of 500 \({}^{\circ}\)C, the maximum temperatures of the two thermocouples were approximately 235.7 \({}^{\circ}\)C and 230 \({}^{\circ}\)C, respectively, as shown in Figure 8b. From this point of view, the temperature difference between these two places inside the concrete was approximately 5.7-7.4 \({}^{\circ}\)C. In addition, even though the target temperature was 500 \({}^{\circ}\)C, the maximum temperature inside the specimen did not yet reach 240 \({}^{\circ}\)C. [PERSON] and [PERSON] [56] pointed out that when the heating temperature of concrete reaches above 200 \({}^{\circ}\)C, cement hydrates gradually decompose. For example, calcium silicate hydrate (C-S-H) colloids begin to lose bonding water. However, the internal temperature of the specimen did not exceed 250 \({}^{\circ}\)C, and the changes in its microstructure and properties were still slight. In other words, the high-temperature test in this study did not cause significant degradation of the matrix of the specimens. This is mainly because the high-temperature furnace was shut down after reaching the set temperature, resulting in the maximum temperature inside the specimen not exceeding the critical temperature of rebar and concrete materials. Therefore, the strength of the specimen did not significantly degrade. The \(\tau\)-\(s\) relationship curves of the unhealed specimens after exposure to high temperatures are shown in Figure 9. As shown in Figure 9, the \(\tau\)-\(s\) relationship curves of the LWAC specimens after exposure to high temperatures could be divided into different stages; that is, linear ascending, nonlinear ascending, and descending stages. Regardless of whether the target temperature was 300 \({}^{\circ}\)C or 500 \({}^{\circ}\)C, there was no significant difference in the peak bond stress between the experimental group and the control group, and the corresponding slip to the peak bond stress was between 1 and 3 mm. On the other hand, each group of specimens that experienced rebar pull-out failure healed themselves according to the aforementioned self-healing method. Once these specimens healed themselves to the planned age, a secondary pull-out test was performed. The test was stopped only when the specimen failed completely; that is, the rebar slippage was no longer limited to 5 mm. Taking each group of specimens exposed to 300 \({}^{\circ}\)C as an example, an obvious plateau appeared in the \(\tau\)-\(s\) relationship curve, as shown in Figure 9a. At this stage, the bond stress decreased slowly, but the slip continued to increase. Then, the bond stress decreased significantly. Overall, the bond-slip curve of each group of LWAC specimens was still consistent with the model suggested by CEB-FIP 2000 [20].