Investigation of the mechanism of spalling of high-strength concrete during fire considering heat, moisture and stress transfer

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In this study, a hypothesis was adopted that the thermal spalling will take place under the effect of pore pressure rise and thermal stress. Pore pressure is created by the evaporation of moisture, while the thermal stress is created by non-uniform temperature profile. To verify the hypothesis, experiments were carried out. Ring compression test is to compress cylinder specimen only at the perimeter region. The compression stress is to simulate the thermal stress during early stage of heating. Fire resistance test is to heat the cylinders and prism rapidly. From the experiments, it was concluded that the spalling takes place where temperature gradient is large. The effect of pore pressure is marginal, because the spalling could take place even after the specimen is cracked. In connection with experiments, numerical simulations on heat conduction and stress distribution were carried out. The results showed the tendency of concentration of thermal stress to the region of spalling.