Study of propagation of ultrasonic pulses in concrete exposed at high temperatures

The concrete exposed to high temperatures, as in the case of fires, can undergo significant physico-chemical changes and loss of durability, through the appearing of cracks, spalling and a gradual deterioration of the hardened cement paste. In this sense, the present work aims to study the effects of concrete exposure at high temperatures on the propagation velocity of ultrasonic pulses. For this, were prepared concrete test specimens with different fck (20, 30, 40 and 50 MPa), exposed to temperatures of 200°, 400°, 600° and 800° C for 30 minutes, the ultrasonic pulse rate being measured before and after the exposure. In addition, an influence of the type of cooling (abrupt and natural) was verified. The results showed that there is only a significant difference in the reduction of the propagation of ultrasonic pulses starting at the temperature of 400 ° C, being the largest reduction factor for the concrete of 20 MPa. Regarding the type of cooling, a variance analysis of the data showed there is no significant difference in the reduction of the speed of ultrasonic pulses.