Characterization of Deep Surface-Opening Cracks in Concrete: Feasibility of Impact-Generated Rayleigh-Waves

The feasibility of impact-generated Rayleigh waves (R-waves) for measuring deep surface-opening cracks in concrete structures was studied. The aim is to contribute to a methodology for simple and effective in-place crack depth estimation. Specimens induced with vertical slits of different depths were prepared for measurement. A two-sensor array was implemented and elastic waves of different central frequencies were generated by mechanical impacts with steel-ball hammers of different ball diameters. R-wave amplitudes were extracted from the waveforms. Attenuation of R-waves due to diffraction and scattering by the slits and the trend of amplitude decaying with slit depth were examined. A reasonable correlation between the amplitude factor and slit depth-to-wavelength ratio was established, which indicated the loss of sensitivity in the change of amplitude factor with regard to dominant wavelengths smaller than the slit depth. By comparing the results of P-wave time-of-flight (TOE) method, the results by measuring again using the proposed method confirmed the feasibility of R-wave attenuation as an alternative parameter for characterizing surface-opening cracks. In addition, it was also demonstrated potential problems associated with the reliability of P-wave TOE method in estimating a crack with limited length.