In the impact-echo method, the presence and the locations of defects in concrete are estimated from identifying peak frequencies in the frequency spectra, which are responsible for the resonance due to time-of-flight from the defects. In practical applications, however, spectra obtained include so many peak frequencies that it is fairly difficult to identify the defects correctly. Stack Imaging of Spectral Amplitudes Based on Impact-Echo (SIBIE) is developed to improve the impact-echo method and to visually identify locations of defects in concrete. SIBIE is an imaging procedure applied to the impact-echo data in the frequency spectra. In this study, the SIBIE procedure is applied to on-site measurement in concrete structures. In order to identify voids in delaminated zones between concrete piers of an express highway and prestressed concrete (PC) panels covered, the impact was driven with two-point detections. For the case of surface cracks, the impact was driven at one side and the detection was conducted at the other side to estimate the depths of cracks. In addition, to identify ungrouted post-tensioning ducts in prestressed concrete, a feasibility study for non-contact SIBIE procedure was conducted in model structures. It is demonstrated that the depths of surface cracks and the locations of internal defects can be identified with reasonable accuracy by SIBIE.
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