Understanding and Assessment of Debonding Failures in FRP-Concrete Systems

Failures in FRP-strengthened reinforced concrete (RC) members may occur by flexural failures of critical sections or by debonding of FRP plate from the RC beams. Debonding in the FRP/adhesive/concrete interface region may cause a significant decrease in member capacity leading to a premature failure of the system. There is a need for improved knowledge of the debonding processes under mechanical and environmental effects. In addition, it is essential to develop appropriate nondestructive evaluation techniques for the inspection of these systems for safe application of strengthening concrete structures using FRP composites. In the first part of this paper, various debonding modes are discussed and modeling techniques are introduced. Effects of moisture and temperature on debonding of these multi-layered systems are described. The second part of this paper introduces a nondestructive inspection technique for FRPstrengthened concrete structures using far-field airborne radar. In this development, emphasis is placed on inspection of debonding in GFRP-wrapped concrete cylinders, but the method would also be applicable to beams and slabs with bonded GFRP composites. Radar measurements on physical laboratory specimens with structural damages are described. The measurement results are provided and numerical simulation and imaging studies are summarized.