## 3 Results and Discussion
### The Effect of the Target Temperature on the Pore Pressure  
#### 3.4.1 The Effect of the Target Temperature on the Pore Pressure of the Oven-Dried Specimens  
The evolution of the pore pressure at a depth of 10 mm from the heated surface of over-dried specimens at a heating rate of 5 \({}^{\circ}\)C/min is shown in Figure 16a. With the increase in the target temperature (from 600 to 800 \({}^{\circ}\)C), the maximum pore pressure of the LWAC slab increased significantly from 102 to 143 kPa, while the maximum pore pressure of the NWC slab increased from 85 to 109 kPa. Furthermore, under the same target temperature conditions, the pore pressure of the LWAC slab at a depth of 10 mm was higher than that of the NWC slab. As for the depths of 30 and 50 mm from the heated surface of the concrete slab, the evolution of the pore pressure is shown in Figure 16b.c. With the increase in the target temperature, the pore pressure of the LWAC slab still increased significantly there, as did the NWC slab. For example, when the target temperature was raised from 600 to 800 \({}^{\circ}\)C, the maximum pore pressure at a depth of 30 mm for the LWAC slab increased significantly from 82 to 153 kPa, while the maximum pore pressure at a depth of 30 mm for the NWC slab increased from 138 to 194 kPa. From the above results, a higher target temperature could cause the maximum pore pressure to occur further from the heated surface. This is because the water vapor from the depth of the heated surface was less likely to transfer, and the higher target temperature could cause the free water trapped in the matrix to evaporate. Therefore, its pore pressure could be increased. However, under the same target temperature conditions, the pore pressures of the LWAC slab at depths of 30 and 50 mm were lower than those of the NWC slab. This situation is opposite to the  
Figure 15: Comparison between the pore pressure and saturated vapor pressure curves. aforementioned case with a depth of 10 mm from the heated surface of the specimen, and this may be due to the low thermal conductivity of LWAC. This can be seen in Figure 10; the temperatures of the LWAC slab at depths of 30 and 50 mm were lower than those of the NWC slab; thus, the pore pressure of these measuring points was also relatively low. Figure 17a shows the evolution of the pore pressure at a depth of 10 mm from the heated surface of oven-dried specimens performed at 10 \({}^{\circ}\)C/min. Under the condition of a target temperature of 600 \({}^{\circ}\)C, the pore pressure of the LWAC slab at a depth of 10 mm was higher than that of the NWC slab. When the target temperature was increased from 600 to 800 \({}^{\circ}\)C, the pore pressure of the LWAC slab increased sharply after being heated for 1 h and then spalled. After 2 h, the pore pressure decreased rapidly due to the spalling, and its value was even lower than the value at 600 \({}^{\circ}\)C. When the heating rate was increased from 5 to 10 \({}^{\circ}\)C/min, the LWAC slab spalled, which resulted in the temperature evolution curve shown in Figure 6f. In contrast, increasing the heating rate did not cause the NWC slab to spall. As for a depth of 30 mm from the heated surface of the concrete slab, the evolution of the pore pressure is shown in Figure 17b. At a target temperature of 600 \({}^{\circ}\)C, the pore pressure evolution curve of the slab was relatively gentle, and the pore pressure of the LWAC specimen was smaller than that of the NWC specimen. When the target temperature was 800 \({}^{\circ}\)C, both the LWAC and NWC slabs had high pore pressures, and the pressure rose sharply. The pore pressure dropped rapidly, and its value was even lower than the value at 600 \({}^{\circ}\)C. This result suggests that high-temperature-induced cracks may help to increase the permeability of the specimen to evacuate water and reduce pore pressure.