2020 Volume 76 Issue 4 Pages 283-292
Non-destructive tests with ultrasonic waves are often used to examine grouting conditions in tendon-duct of post-tensioned prestressed concrete bridges. Wide-range ultrasonic testing (WUT), a kind of the NDT technique, has an advantage that it is applicable even in relatively thick PC girders. WUT is often employed in box-girders of PC bridge because the grout inspection can be conducted at the inner space of the girder without a scaffolding. WUT analyses the reflection ultrasonic waves and evaluates voids from the observed high-frequency waves. The observed ultrasonic waves include reflection waves from the end-face of girder in addition to the reflection waves from the voids. It is well known that the former reflection waves are generally greater than the latter. The influence of reflection waves from the end-face should be evaluated properly to detect the voids of PC duct. To improve the accuracy of void detection by WUT, this study aims at examining the influence of reflection waves from the duct and the end-face. The study conducted the fundamental experiment using 4 test specimens: A) concrete embedding a void-duct; B) concrete embedding a grout-filled duct; C) plain concrete of 240 mm thick; and D) plain concrete of 135 mm thick. The paper reports the influence of reflection waves from the end-face on the void detection of WUT.