Performance degradation and microscopic structure of glazed hollow bead insulation normal concrete after exposure to high temperature

The normal concrete (NC) and glazed hollow bead insulation normal concrete (GHB/NC) were made for studying the process of performance degradation from normal temperature to 1 000℃, which including changes in apparent phenomena, loss of mass and compressive strength. Simultaneously, the adaptation of ultrasonic test in evaluating the performance of concrete after exposure to high temperature was investigated. The relationships between relative velocity, damage degree and temperature, compressive strength loss rate were comparative analyzed. The micro-structure changes of concrete specimens after exposure to different high temperatures were observed by SEM. The results show that it has good correlation of the parameters of relative velocity and damage degree in evaluating the performance of concrete after high temperature. The regression formula has a good fitting degree. With the rise of heat temperature, the internal damage of concrete is gradually intensified, cement hydrates decomposes and water disperses, which causes voids, cracks and interpenetration occurred on the surface and inside of the specimens. The bonding force between glazed hollow bead, coarse aggregates and cement paste is gradually weakened or even lost. These cause deterioration of macroscopic mechanical properties and increasing of compressive strength loss rate of GHB/NC and NC. After experiencing the high temperature of 800℃, the losses in compressive strength of NC and GHB/NC are 72.3% and 74.6%, and the bearing capacity is almost lost after exposure to 1 000℃.