Application of Impact Resonance C-Scan Stack Images to Evaluate Bridge Deck Conditions

This study presents a practical approach for imaging concrete pavement and bridge deck slabs for the presence of delamination defects. Air-coupled impact resonance (impact-echo) test data are presented as a fused image by using stacked spectral C-scans of the tested deck surface. The low frequency (<6 kHz) dynamic vibrational response of delamination defects, primarily caused by the behavior of flexural vibration modes, clearly and accurately reveals the presence of internal shallow delamination defects. Images are constructed with data from air-coupled impact resonance tests carried out on laboratory and field concrete deck samples and an in-service concrete bridge deck. The test data are arranged along surface x- and y-coordinates, with spectral amplitude represented by a coupled gray scale–opacity index. The image parameters are defined by data-driven rule-based criteria, with the presence of near-surface delamination defects indicated by shaded regions. The data manipulation and image construction processes are carried out by using commercially available software and a conventional personal computer. The results demonstrate the utility and accuracy of air-coupled testing in conjunction with the stacked C-scan imaging approach.