Effects of the cooling treatment on the dynamic behavior of ordinary concrete exposed to high temperatures

The dynamic properties of normal-strength concrete are considered to investigate its behavior in compression after heating to high temperature (maximum of 600 degrees C) and cooling down to room temperature via air cooling or water cooling. Dynamic compression tests are performed using a 50-mm Split Hopkinson Pressure Bar (SHPB) for strain rates ranging from 50 to 220 s(-1), while quasi-static compression tests are also performed. The effects of cooling on the dynamic compressive strength, elastic modulus, P-wave velocity, and failure modes are discussed in detail. In the quasi-static tests, the impact of water cooling on the strength in compression of concrete is more severe than that of air cooling, while there are no sizeable differences in terms of the P-wave velocity and density below 600 degrees C. In the dynamic tests, water cooling is more detrimental to the dynamic strength and to the dynamic increase factor (DIF) as compared with air cooling under the same test conditions. DIF increases with temperature after both water and air cooling. The tests also show that higher strain rates produce smaller fragments due to specimen crushing (T <= 400 degrees C). Furthermore, for the same maximum temperature and strain rate, water cooling produces more irregular and smaller fragments than air cooling. (C) 2020 Elsevier Ltd. All rights reserved.