Remote Detection of Debonding in FRP-strengthened Concrete Structures Using Acoustic-Laser Technique

Abstract Fiber-reinforced polymer (FRP) strengthening and retro fi tting of concrete elements, such as beams, columns, slabs, and bridge decks, have become increasingly popular. Nonetheless, rapid and reliable nondestructive testing techniques (NDT) that are capable of remotely assessing in-situ integrity of retro fi tted systems are needed. Development of a robust NDT method that provides an accurate and remote assessment of damage and fl aws underneath the FRP plates/sheets is required. In this study, a NDT based on an acoustic-laser system is proposed for remote detection of debonding in FRP-strengthened concrete structures. This technique utilizes the difference in dynamic response of the intact and the debonded regions in a FRP-strengthened concrete structure to an acoustic excitation, which is then measured using laser vibrometry. Feasibility and accuracy of the technique were investigated through a series of measurements on laboratory-sized plain, reinforced, and FRP-strengthened concrete specimens. It was shown that the difference in dynamic response could be captured by the acoustic-laser system and is in good agreement with simple calculations.