Lamb Waves for Detecting Delamination between Steel Bars and Concrete

Traditional ultrasonic methods for inspecting defects in concrete are good for detecting large voids in concrete, but are not very efficient for detecting delamination at the interface between concrete and steel bars. This paper investigates the feasibility of detecting interface degradation and separation of steel bars in concrete beams using generalized Rayleigh-Lamb waves and cylindrical guided Lamb waves. The Lamb wave can propagate a long distance along the reinforcing steel bars as the guided wave and is sensitive to the interface bonding condition between the steel bar and the concrete. A special coupler between the steel bar and ultrasonic transducers has been used to launch nonaxisymmetric guided waves in the steel bar. The results of this investigation show that the proposed transducer-receiver arrangements can successfully inspect reinforced concrete beams for delamination at the steel-concrete interface. Directions for further research are suggested.