Quantitative Non-Destructive Evaluation of FRP Laminate-Concrete Bond Strength Using Ultrasound Tomography

Fiber-reinforced polymer (FRP) laminate is one of the most popular and practical solutions for the strengthening and retrofitting of deteriorated or under-strengthened concrete structures, adding strength, ductility, and durability. The quality of the FRP–concrete bond is critical in stress transfer and composite action at the interface, and in situ evaluation of the bond strength is a challenging issue. To quantitatively evaluate the bond strength, nondestructive evaluation (NDE) with ultrasound tomography was utilized on 32 small-scale concrete beams strengthened with carbon FRP laminates. Various parameters that may affect the bond strength, such as surface roughness, surface voids, epoxy type and thickness, and FRP type, were considered. The associated bond capacities were found through a bending test and correlated through finite element modeling. Quantitative relationships involving the NDE output values and associated bond strengths, with parametric inputs, were developed. Simple numeric examples are provided, showing application of the developed equations, which will be very useful in estimating the in-service bond conditions of applied FRP laminates on concrete structures. This may lead to quantitative estimation of the expected strength contribution of the laminates to the overall flexural capacity of structural members.