Case studies on ungrouted tendon-duct in prestressed concrete models by SIBIE

The impact-echo method has been widely applied to identification of defects in concrete. The presence and the location of the defect are estimated from identifying peak frequencies in the frequency spectra, which are responsible for the resonance due to time-of-flight from the defect. In practical applications, however, spectra obtained include so many peak frequencies that it is fairly difficult to identify the defect correctly. In order to circumvent the fact, Stack Imaging of Spectral Amplitudes Based on Impact-Echo (SIBIE) procedure is developed to visually identify the location of the defect.In this study, the procedure is applied to two types of concrete specimens. One type contains grouted and ungrouted sheaths for post-tensioning tendon-ducts. The other specimen with an ungrouted duct is tested to investigate the sensor selection.It is demonstrated that the ungrouted tendon-duct can be identified with reasonable accuracy by the SIBIE procedure. Both an accelerometer and a laser-vibrometer are available for the SIBIE analysis.