## 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  
Under room-temperature conditions, the failure modes of the specimens in each group showed rebar pull-out failure. One characteristic of this phenomenon is that the longitudinal rebar of the specimen was pulled out of the concrete, while only a few cracks appeared in the surrounding concrete. In other words, no splitting failure occurred in the specimen during the pull-out test process. This can be attributed to the presence of stirrups, which effectively confined the specimen and limited the development of cracks. In this study, the concrete cover of the pull-out specimens was 6.5 cm and surrounded by transverse stirrups. The concrete between the transverse ribs was sheared off due to punching, causing the rebar to be pulled out of the concrete directly. Generally speaking, if the concrete cover-to-diameter of the rebar (\(C/D\)) ratio of the pull-out specimen is within the range of 2.5-3.0, the failure mode is mostly rebar pull-out failure [52]. The \(C/D\) ratio of the pull-out specimen in this study was 3.4; thus, all the pull-out specimens suffered rebar pull-out failure. The literature data shows that the rebar slipping at the end of the peak bond stress of the pull-out specimen is roughly in the range of 2-6 mm [20; 53]. In view of this, the first pull-out test of the specimen was terminated when the rebar slippage reached 5 mm. Then, the damaged specimens were allowed to heal themselves in a planned manner before conducting a secondary pullout test. Therefore, when analyzing the first pull-out test of each group of specimens, the slip amount of the rebar was limited to the range of 0 to 5 mm. The local bond stress-slip (\(\tau\)-\(s\)) relationship curves of the pull-out tests for each group of specimens at room temperature are shown in Figure 6.  
As shown in Figure 6, with the increase in load, the curves of each group of specimens in the pull-out test could be divided into linear ascending, nonlinear ascending, and descending stages. Notably, the ascending branch of the \(\tau\)-\(s\) relationship exhibited linear behavior. In addition, the surfaces of the specimens that suffered pull-out failure exhibited  
Figure 5: Compressive strength and elastic modulus of LWAC. neither any splitting cracks nor any sudden drop in bond stress when it reached its peak. The peak bond stress of Groups B and C was slightly higher than that of Group A, but the corresponding slip to the peak bond stress was smaller, and its value was about 1-3 mm. Figure 7 shows the bond strength of the first pull-out test for each group of specimens. As shown in Figure 7, at room temperature, the average bond strengths of each group at the age of 28 days were close to 28 MPa. The standard deviations of the compressive strength of Groups A, B, and C were 1.56, 1.34, and 0.40 MPa, respectively. These bond strength values significantly exceeded the values recommended by [PERSON] et al. [19] and the CEB-FIP standard [20]. This is mainly attributed to the stronger overall interlocking effect of the LWAs. 2.2 Local Bond-Slip Relationship and Bond Strength in Unhealed LWAC after Exposure to High Temperatures  
According to the plan, the high-temperature test was conducted immediately after the specimens were cast and cured for 28 days. The high-temperature test used a faster heating rate; that is, 10 \({}^{\circ}\)C/min. Once the high-temperature furnace reached the target temperature, the power was turned off. After exposure to 300 \({}^{\circ}\)C and 500 \({}^{\circ}\)C, there was no obvious spalling of the two groups of LWAC specimens. Theoretically, a longer embedded length of rebar will lead to strain penetration [54], which makes the strain distribution of the rebar along the longitudinal direction uneven, resulting in lower bond strength in the concrete. In the pull-out test, the bond anchorage length of the rebar was set to be short (\(l_{e}=3d_{b}\)). Therefore, the rebar remained in the elastic stage [55].