The Temperature and Pore Pressure Distribution of Lightweight Aggregate Concrete Slabs Exposed to Elevated Temperatures

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Concrete has good fire resistance. However, once exposed to rapidly increasing temperatures, concrete may suffer from thermal stress-induced spalling or pore pressure-induced spalling. Compared with normal-weight concrete (NWC), lightweight aggregate concrete (LWAC) has a low thermal conductivity and is more prone to cause a higher temperature gradient under the action of high temperatures. This poses a hidden concern to the fire safety of general LWAC structures. Therefore, this study aimed to investigate the temperature and the pore pressure distribution of LWAC slabs under one-dimensional heating tests and to compare them with NWC slabs. The test variables were the moisture content of the specimen (oven-dried and air-dried), target temperature (600 and 800 °C), and heating rate (5 and 10 °C/min). The temperature and the pore pressure distributions were measured separately by thermocouples and pressure gauges embedded in different positions of the specimen. The test results show that the maximum pore pressure (Pmax) of the LWAC slabs was generally higher than that of the NWC slab at a distance of 10 mm from the heated surface when the specimen was in an oven-dried state. However, at 30 and 50 mm from the heated surface, the Pmax of the NWC slab tended to be higher. This shows that the Pmax distribution of the LWAC slab was closer to the heated surface when the specimen was in an oven-dried state, while the Pmax of the NWC slab occurred further from the heated surface. Further, as the heating rate increased, a higher pore pressure was generated inside the specimen and the pressure rose more rapidly. In particular, at a target temperature of 800 °C and a heating rate of 10 °C/min, the corner spalling phenomenon appeared on the air-dried LWAC slab.