Impact-Echo method (I-E) is treated as the one of the most promising nondestructive techniques for assessment of concrete structures. This method can be also applied for evaluation of multi-layer systems created during repair of concrete. The stress wave generated in the I-E method has lower sensitivity to natural heterogeneity of concrete structure because of its lower frequency. Additional feature of I-E method is an application of frequency spectrum analysis obtained by fast Fourier transform of waveform. Recently, a new tool for signal analysis – wavelet analysis - is being implemented in NDT assessment, also in the case of concrete structures. It is a multiresolution time-scale methods which enables to extract information like instantaneous frequency, tiny echoes embedded in complex signal or to suppress noise.

In this work the effect of quality of interface: polymer-cement coating – concrete substrate on propagation of stress wave in I-E method was analyzed. The several repair systems were tested. They were differed in concrete surface quality (as a result of applying surface treatments) and presence of bond coat. For each repair system the wavelet analysis of impact-echo signals was performed. The effects of concrete surface quality and presence of bond coat on the results of the signal wavelet analysis were discussed.

The research project was granted by Polish Scientific Research Committee - grant number KBN 4 T07E 027 27.

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1. Computer simulation of stress wave propagation in repair systems
2. Characterization of concrete surface geometry by laser profilometry
3. On the effect of concrete substrate roughness on stress wave propagation in repair systems