Mechanical Properties and Damage Mechanism of Shale Ceramsite Concrete after High-Temperature Treatment

The high-temperature resistance of lightweight shale ceramsite concrete (LWSCC) is seriously underestimated because the effect of moisture is not considered. To investigate the mechanical properties and damage of LWSCC after a high-temperature treatment, strength tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were carried out, and a nondestructive ultrasonic testing device was used to quantify the damage. The results show that the spalling characteristics of LWSCC at high temperatures were closely related to its water content. The axial compressive strength of LWSCC linearly decreased with increasing target temperature. LWSCC showed a greater resistance to high-temperature deterioration than NWC with the same mass loss ratio. LWSCC with a moisture content of 4.1% had a high probability of spalling at temperatures above 500 degrees C. However, dry LWSCC had a low probability of spalling even when heated to 800 degrees C. Water in shale ceramsite with a porous structure was identified as a critical factor in the high-temperature deterioration. After the temperature exceeded 200 degrees C, the high-pressure steam in the ceramsite expanded the cracks. These findings provide a basis for designing LWSCC with high-temperature resistance and evaluating the safety of LWSCC buildings after fires.