Abstract
The impact-echo method is a nondestructive evaluation to detect the presence of voids within tendon ducts in prestressed concrete structure. The presence of voids in concrete is estimated by identifying peak frequencies in the spectrum. However, the detection for ungrouted ducts is not always successful because many peaks are often observed in the spectrum due to reflection at other reflection sources. In order to solve this problem, a new procedure is developed by applying an imaging procedure to the impact-echo data, known as stack imaging of spectral amplitudes based on impact-echo (SIBIE). In this study, impact-echo method is performed on the webs of post-tensioned girders on existing PC bridges to survey the presence of ungrouted ducts. To detect the voids within tendon ducts, the SIBIE procedure is applied. Applicability of SIBIE was verified at selected locations invasively by drilling and observing the interior of the tendon duct. Results show many peaks caused by reflection and so forth are observed in frequency spectra by impact-echo tests. Thus, it is difficult to extract the particular peaks associated with only the locations of void. In contrast, it is confirmed that the presence and location of ungrouted ducts can be visually identified by SIBIE analysis. After the SIBIE analysis is completed, the analytical results are compared with those obtained by invasive observation. Thus, the feasibility of SIBIE on detection of voids within tendon ducts in existing PC bridges is demonstrated.
