Debonding detection in rebar-reinforced concrete structures using second harmonic generation of longitudinal guided wave

Nonlinear features of ultrasonic guided waves (GWs) is studied for debonding detection and location estimation in rebar reinforced concrete structure. The study shows that the presence of debonding between steel rebar and concrete surface produces breathing phenomenon causing contact acoustic nonlinearity (CAN), which generates second harmonics. Time-frequency analysis is used to estimate the location of debonding in this study. At a particular frequency, embedded rebar has much greater number of wave modes in bare rebar. To avoid unnecessary complexity, only longitudinal GW modes for bare and embedded rebar are excited and received to detect and locate debonding. To precisely determine the wave mode at excited frequency and frequency of second harmonics, frequency-wavenumber analysis is performed using 2D-Fast Fourier Transform of time-space data. Three-dimensional explicit finite element simulations are performed for various case studies and the model is validated by experimentally measured data. The results of this study show that the proposed method is practically viable and beneficial for debonding detection and location estimation in reinforced concrete structures.