Nonlinear Ultrasonic Method to Evaluate Residual Mechanical Properties of Thermally Damaged Concrete

Abstract

An experimental study has been carried out to evaluate the residual mechanical properties of thermally damaged concrete using a nonlinear ultrasonic method. A nonlinearity parameter was measured by the impact-modulation technique, which sensitively reflects the degree of thermal damage in concrete. Key mechanical properties, compressive strength, elastic modulus, and peak strain were obtained from compressive stress-strain curves of cylindrical concrete samples. The correlations between the nonlinearity parameters and the mechanical properties were investigated for various conditions: high-temperature exposure time of 1, 2, and 3 hours and four different mixture proportions. The authors thereupon developed regression equations that can predict the residual mechanical properties from the measurement of a nonlinearity parameter, which indicates the degree of thermal damage.