## 2 Experimental Programs
### Testing Methods  
The concrete slump was carried out in accordance with ASTM C143 [43]. The concrete unit weight was determined in accordance with ASTM C138 [44]. Cylindrical concrete specimens were tested for compressive strength according to ASTM C39 [45], and their static modulus of elasticity were tested according to ASTM C469 [46]. The compressive strength and static modulus of elasticity were the average values of three specimens. The pull-out test was carried out following the specifications of ASTM C234 [47]. A 200 kN MTS servo valve-controlled machine equipped with a special test frame was used to apply the tensile force to the pull-out specimen, as shown in Figure 3.  
The embedded rebar of the pull-out specimen was loaded at one end and was set to a free state at the other end, as shown in Figure 3a. Three linear variable differential transformers (LVDTs) were set up using a test frame, as shown in Figure 3b. The purpose is to measure the relative slip between the longitudinal rebar and the surrounding concrete. During the entire pull-out test process, displacement control was adopted. The load was applied at a constant displacement rate of 0.01 mm/s. In the first pull-out test, the test was stopped when the slippage of the specimen reached 5 mm. In the secondary pull-out test, the test was terminated only when the specimen failed completely. Figure 3: Setup of the pull-out test: (**a**) overall configuration; (**b**) local configuration. Figure 2: Configuration of the pull-out specimen: (**a**) transverse section; (**b**) longitudinal section; (**c**) photo of the specimen mold. Assuming that the bond stress is uniformly distributed along the length of the steel bar, the bond stress can be calculated as follows [48]:  
\[\tau=\frac{P}{\pi d_{b}l_{e}} \tag{1}\]  
where \(\tau\) = the bond stress; \(P\) = the applied load; \(d_{b}\)= the rebar diameter; and \(l_{e}\) = the embedded length. After the specimens were cured for 28 days, the incubator was adjusted to 60 \({}^{\circ}\)C for five days to dry the moisture inside the concrete specimens, to reduce the risk of the specimens spalling at high temperatures. To understand the relationship between the temperature of the concrete inside the pull-out specimen and the heating time, thermocouples were embedded at different places inside the specimen. Two thermocouples were embedded in the 150 mm cubic concrete block of the pull-out specimen: one 2 cm away from the surface of the specimen and the other 4 cm away (as shown in Figure 4). When the specimen was subjected to high-temperature testing, the heating rate of the high-temperature furnace was 10 \({}^{\circ}\)C/min. After the target temperature was reached, the power supply of the high-temperature furnace was turned off immediately. After the specimens were naturally cooled to room temperature in the high-temperature furnace, the residual bond strength (BS) was tested. The pull-out test was divided into five types according to the state of the LWAC specimen. The test sequences for these five types of pull-out tests are shown in Table 3.  
Furthermore, field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) were used to conduct microscopic morphology and elemental analysis of the precipitation. The cylindrical concrete specimen damaged after the compression test was used for FESEM observation. Samples were taken from two different parts of each group of cylindrical specimens; that is, two centimeters near the surface and the center. In addition, X-ray diffraction (XRD) analysis was used to determine the type of crystals that precipitated. Figure 4: Thermocouple for the pull-out test specimen: (**a**) schematic diagram of the location of the thermocouple; (**b**) actual pull-out specimens.