The spalling mechanism of high-strength concrete under fire

The spalling properties of concrete were investigated in relation to surface moisture content. Changes in the microstructure of concrete, moisture transfer and internal pressure were also investigated from a microscopic aspect. Based on the results of the investigation, experimental research was conducted on the effects of heat and moisture transfer on spalling as well as the causes of vapour pressure (internal stress) surges and spalling. Spalling of high-strength concrete was found to be significantly affected by moisture transfer in the surface region of concrete and moisture transfer was found to be closely related to the temperature profiles resulting from the characteristics of pore structures, which are the main passages for moisture. It was also found that, in the high-strength (80 MPa) concrete used in this study, the probability of spalling and scale of damage could be reduced according to dryness in the surface region (0–30 mm depth).