Nondestructive Evaluation: Nonlinear Ultrasound to Evaluate the Integrity of Thermally Damaged Concrete

International audienceThe objective of this research project was to establish the feasibility of using a nondestructive evaluation technique based on nonlinear ultrasound for determining the depth and degree of microcracking near the surface of concrete and to assess the degree of sensitivity of such a technique. This objective was reached by combining linear and nonlinear measurements associated with numerical simulation.First, the global effect of thermal damage on concrete’s linear and nonlinear properties was studied by resonance inspection techniques. It was shown that standard pulse wave speed techniques are not relevant for extracting the mechanical properties of concrete. The high sensitivity of measured nonlinearity was shown and served as a validation tool for the rest of the study, that is, probing the material nonlinearity at various depths through the use of time-reversal elastic nonlinearity diagnostics (TREND). The basic idea of probing the material nonlinearity at various depths by changing the frequency was validated by exhibiting a similar trend as nonlinear resonance measurements. At the end of this report, the potential for applying these procedures to real concrete structures are addressed