Fiber-reinforced polymer (FRP) strengthening and retrofitting of concrete structural elements in civil infrastructure systems has become increasingly popular since the 1990s, especially in areas where earthquakes are prevalent [1,2]. When defects such as voids or delamination occur in these FRP-reinforced concrete elements at the FRP-concrete interface, the FRP obscures the defect such that visual detection may not be possible. Detection of such defects is especially important in the case where FRP has been retrofitted to previously damaged structures and further damage is a distinct possibility.
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