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The Acoustic-laser Vibrometry Technique for the Noncontact Detection of Discontinuities in Fiber Reinforced Polymer-retrofitted Concrete

Fiber reinforced polymer (FRP) retrofitted concrete is a composite material system that is commonly used in construction for its improved strength properties or for rehabilitation of concrete structures. This material system is composed of a concrete substrate on which FRP is adhered with an epoxy matrix. When the system is subject to adverse mechanical or environmental effects, delamination of the FRP or damage at the FRPconcrete interface may occur, yet remain externally undetected because the damage is obscured by the FRP. In this paper, a robust standoff technique for finding discontinuities in FRP-retrofitted concrete at the FRP-concrete interface using a combined acoustic-laser vibrometry technique is presented. Experiments were conducted on a test specimen with a cubic discontinuity at the FRPconcrete interface. The frequency signature of the discontinuity, which provides a technique for determining the approximate size of the discontinuity, was found to be in agreement with theory. An image was constructed with a series of measurements that show the boundary and spatial vibrational behavior of the discontinuity. From that series of measurements a probability of detection and receiver operating characteristic curve was determined for the methodology. Estimates of the area rate of coverage of measurement for an operational system and suggestions for future studies are given.

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