Effect of heating and cooling regimes on residual strength and microstructure of normal strength and high-performance concrete

A research program was carried out to investigate the residual compressive strength of high-performance concrete (HPC) and normal strength concrete (NSC) after they were exposed to high temperatures, 800 degrees C and 1100 degrees C, and two cooling regimes. Test results obtained showed that compared with the strength at room temperature, the residual strength of both HPC and NSC dropped sharply after exposure to high temperatures. Water cooling, which resulted in a significant thermal shock, caused a bit more severe deterioration in strength compared to furnace cooling. Thermal shock was not necessarily the primary cause for spalling in HPC. Mercury intrusion porosimetry tests were carried out to measure variation in the pore structure of concrete. Significant changes in the cumulative pore volume curves before and after high temperatures in both NSC and HPC were observed. The cumulative pore volume of HPC increased more remarkably than that of NSC. The difference between the effects of the two cooling regimes on mechanical property as well as the microstructure decreased at 1100 degrees C when compared 800 degrees C. (C) 2000 Elsevier Science Inc. All rights reserved.