Lamb waves for detecting delamination between steel bars and concrete

The feasibility of detecting interface degradation and separation of steel bars in concrete beams using Lamb waves is investigated in this paper. The Lamb wave can propagate a long distance along the reinforcing steel bars embedded in concrete as the guided wave and is sensitive to the interface bonding condition between the steel bar and the concrete. The traditional ultrasonic methods for inspecting defects in concrete use reflection, transmission, and scattering of longitudinal waves by internal defects. These methods are good for detecting large voids in concrete, but they are not very efficient for detecting delamination at the interface between concrete and steel bars. In this study, a special coupler between the steel bar and ultrasonic transducers has been used to launch nonaxisymmetric guided waves in the steel bar. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool,for health monitoring of reinforced concrete structures.