Evaluation of the Depth of Surface Deterioration for Concrete Structure Using Dispersion Characteristics of Surface Wave

Surface waves generated by an impact are used to assess depth of deterioration for concrete plate. The proposed method uses one receiver positioned away from the impacting source. The spectrogram of the group velocity obtained from the signal recorded from the receiver is calculated by Short-Time Fourier Transform and the reassignment technique. Experiments were conduct on the concrete plate with top mortar layer to simulate concrete with serious aggregate segregation and bleeding. In the experiment, the responses corresponding to different source-receiver distance were explored. The results were shown by both slowness spectrogram and velocity profile. In the slowness spectrogram, substantial increase of velocity at low frequency domain is found. The velocity profile shows the change of wave speed is at the wave length about 1.2 times the mortar thickness. The results also show the lower velocity corresponding to the weak layer may be identified for source-receiver distance as short as 0.5 m but the wave speed may be underestimated.