The sensitivity of surface guided modes to the bond quality between a concrete block and a composite plate

Ultrasonic modes guided along the surface of a concrete block covered by a composite plate are investigated. First of all, the propagation phenomenon is studied by predicting the dispersion curves for various modes supposed to exist in this structure. Then, focus is made on a specific mode expected to be sensitive to the quality of the bond between the concrete and the composite, according to its through-thickness displacement field. Its dispersion curve is re-plotted for various states of this bond, which is modelled as a thin layer with varying properties. Limit cases corresponding to total disbond and perfect bond are considered. Experiments are then made on two composite-concrete assemblies for these two extreme cases using a contact PZT transmitter and an air-coupled receiver system. The phase velocities are in good agreement with the predicted dispersion curves, thus showing the potential of the ultrasonic guided mode to control the quality of bonds in such structures.