Thermal modulation of nonlinear acoustic wave for concrete damage evaluation

Nonlinear ultrasonic methods such as nonlinear resonance acoustic spectroscopy (NRAS) and nonlinear wave modulation spectroscopy (NWMS) show higher sensitivity to microcracking damage in concrete than the conventional linear ultrasonic testing methods. However, the NRAS method are only applicable to small specimens, and the NWMS method needs complicate and expensive equipment. In this work a method using thermal modulation of nonlinear ultrasonic waves is proposed. Ambient temperature change excites and modulates nonlinear behavior of ultrasonic waves in concrete with microcracks. Coda wave interferometry is used to analyze the relative velocity change with temperature that is defined as thermal-modulation coefficient. Experiments were performed on concrete samples with mechanical damage and thermal damage. Results indicate that the concrete samples with higher damage level demonstrated higher relative velocity change to temperature variation. Therefore the thermal-modulation coefficient can be used as a nonlinear parameter for concrete damage characterization.