Multi-Bandwidth Wavelet Transform of Impact Echo Signals for Delamination Detection of Thin Concrete Slabs

In this study, a multi-bandwidth wavelet transform of signals with mixed frequencies from multiple delamination mechanisms is proposed to achieve the time and frequency resolution required in delamination detection. It was applied to detect six embedded defects, simulating shallow and deep delamination, in a 60 in. x 36 in. x 7.25 in. reinforced concrete slab from impact echo signals recorded at 40 points using a portable seismic property analyzer. Test results indicated that the proposed transform successfully detected all the defects and was twice as accurate as Fourier transform for the identification of resonant frequencies. Out of the 40 measurement points, the false detection points were reduced from 22 with Fourier transform to 10 with the proposed transform.