Vertical spectral tomography of concrete structures based on impact echo depth spectra

This paper proposes a vertical spectral tomography for use in nondestructive testing of concrete structures. Impact echo tests are conducted along a test line on the concrete surface. Then, the response curves are transformed into depth spectra. Arranging the depth spectra in parallel and representing the amplitude by color scale, one obtains an image of the vertical cross-section under the test line. Three types of spectral tomograms are proposed. Numerical and experimental tests are performed to verify and compare the tomograms. Although different types of tomograms possess different attributes, all three tomograms can depict the internal crack successfully. The internal crack is represented by bright stripes in the tomograms, which can be used to estimate the size and location of the crack. The vertical spectral tomogram provides a direct image of the concrete cross-section. It may serve as a useful tool in the nondestructive inspection of concrete structures.