Spalling of heated high performance concrete due to thermal and hygric gradients

In this study, high performance concrete beams and prisms with high content of PFA were heated to various temperatures up to 450ºC at the heating rates of 1ºC/min, 3ºC/min and 10ºC/min. The thermal gradient was found to increase first with the heating time until a peak value was reached and then decrease until the thermal equilibrium was reached, measured as 115ºC, 240ºC and 268ºC for the three heating rates. Spalling occurred on some specimens when the heating temperature was over 400ºC for heating rates of 3ºC/min and 10ºC/min. The hygric gradient was found to reach its maximum when the thermal gradient reached its peak. This study indicates that spalling of HPC could happen when the heating temperature was high enough, and both thermal and hygric gradients reached their maxima.