Detecting the Depth of Concrete Deterioration Using Rayleigh Wave Dispersion Based on Time-Frequency Analysis

摘要

The objective of this paper is to study the feasibility of using the dispersion curve of Rayleigh wave (R-wave) to evaluate the depth of concrete deterioration. In this paper, numerical analysis was performed on a 2D axisymmetric model consisting of two layers with different material properties. The top layer with a thickness of 40 mm had weaker material properties than those of the bottom layer to simulate the surface deteriorated concrete. Mechanical impact having a contact time of 50 μs was applied at a point on the top surface of the model and the displacement responses at points having various distances away from impact were recorded and analyzed. The numerical results show that the dispersion of R-wave can be observed in the displacement waveforms. However, one can have a better observation of the R-wave dispersion phenomenon at points far away from impact. The Morlet wavelet transform was carried out on the waveforms to obtain the time-frequency spectra. Subsequently, the time-frequency spectra can be used to construct the dispersion curve of R-wave. It is found that the phase velocity of R-wave increases with increasing wavelength as the wavelength is longer than twice the thickness of the top layer. Thus, the depth of the deteriorated concrete can be identified to be the half of the wavelength that makes a continuous increase in the R-wave velocity in the dispersion curve.