ULTRASONIC TESTING OF CONCRETE AFTER EXPOSURE TO HIGH-TEMPERATURES

Effects of high temperatures on the velocity of ultrasonic pulses in concrete have been studied experimentally. Concrete prisms made of different mixes were heated in an electric muffle furnace to varying temperatures up to 800 degree C and pulse velocity was measured before and after heating. The compressive strength of the concrete was determined later by crushing the prisms. It was found that pulse velocity decreased with increase of temperature at an increasing rate. Post-heating treatment significantly affected the test results: pulse velocity measured after quenching test specimens in water was always higher than that for the corresponding specimens cooled in air, probably due to the increase in concrete moisture content which in turn increased the pulse velocity. Regression analysis of the test results has led to correlations between the residual pulse velocity and the residual compressive strength expressed as fractions of the original values before heating.