## 3 Results and Discussion
### The Effect of the Moisture Content on the Pore Pressure
#### 3.6.2 Concrete Slabs Exposed to a Target Temperature of 800 \({}^{\circ}\)C  
The evolution of the pore pressure at a depth of 10 mm from the heated surface of the concrete slab, at a target temperature of 800 \({}^{\circ}\)C and a heating rate of 5 \({}^{\circ}\)C/min, is shown in Figure 26a. Both the LWAC and NWC slabs showed higher pore pressures in the oven-dried state. The maximum pore pressures of the LWAC slabs in oven-dried and air-dried states were 143 and 93 KPa, respectively. At 30 mm from the heated surface (as shown in Figure 26b), the LWAC slab also showed a higher pore pressure in the oven-dried state. However, the curves of the NWC slabs in the oven-dried and air-dried states were relatively close. At 50 mm from the heated surface (as shown in Figure 26c), the pore pressure of the LWAC slab in the air-dried state was significantly higher than that of the oven-dried state, while the NWC slab showed no significant difference. The results show that, at a lower heating rate, the pore pressures of the LWAC specimens with different moisture contents near the heated surface were not significantly different. This is because the slower heating rate allowed the water vapor near the heated surface to have sufficient time to gradually transport into the interior of the specimen through the internal pores. However, at a deeper distance from the heated surface, because LWAC had more pores, its internal water content was larger in the air-dried state. In addition, the water vapor  
Figure 24: Effect of the moisture content on the pore pressure of the specimens performed at a target temperature of 600 \({}^{\circ}\)C and heating rate of 5 \({}^{\circ}\)C/min: (**a**) 10; (**b**) 30; (**c**) 50 mm depths.  
Figure 25: Effect of the moisture content on the pore pressure of the specimens performed at a target temperature of 600 \({}^{\circ}\)C and heating rate of 10 \({}^{\circ}\)C/min: (**a**) 10; (**b**) 30; (**c**) 50 mm depth.  
near the heated surface was transported to the back of the specimen due to the heating, resulting in a more significant increase in the pore pressure in the deeper part.  
The evolution of pore pressure at a depth of 10 mm from the heated surface of the concrete slab, at a target temperature of 800 \({}^{\circ}\)C and a heating rate of 10 \({}^{\circ}\)C/min, is shown in Figure 27a. The LWAC slab showed a high pore pressure in the air-dried state, and the pressure suddenly rose and then dropped sharply. This was because of the increase in the pore pressure due to the rapid evaporation of water vapor under the condition of a higher heating rate with a higher moisture content. The maximum pore pressures of the LWAC slabs in oven-dried and air-dried states were 344 and 893 kPa, respectively. The NWC slab also showed a similar trend. However, at a distance of 30 mm from the heated surface (as shown in Figure 27b), the LWAC and NWC slabs showed higher pore pressures in the oven-dried state, which was different from the results at 10 mm. The reason for this might be that the pore pressure at 10 mm in the air-dried state rapidly rose, resulting in cracks in the specimen, which caused the steam here to escape more easily; thus, the pore pressure was lower. At a distance of 50 mm from the heated surface (as shown in Figure 27c), the LWAC slab showed a higher pore pressure in the air-dried state, while the NWC slab showed no obvious difference.