Damage detection in concrete using lamb waves

The feasibility of detecting defects in concrete beams using Lamb waves is investigated in this paper. The Lamb wave can propagate a long distance along the specimen as the guided wave and is sensitive to defects that are smaller than its wavelength The traditional ultrasonic methods for inspecting defects in concrete use reflection, transmission and scattering of longitudinal waves by internal defects. In traditional techniques signal amplitude and time of night measurements provide information about the internal, defects in concrete. These methods are time consuming and often fail to detect a variety of defects, such as internal corrosion, honeycombs, closed cracks and small inclusions. In this paper Lamb waves are used to detect those defects in concrete beams with and without reinforcement. The Lamb wave technique is found to be reliable for detecting such defects. The effect of separation or delamination between concrete and reinforcing steel bars on the Lamb wave propagation characteristics is also investigated. Corrosion of rebars can cause this delamination. It is found that the cylindrical guided waves propagating along the steel rebars are very sensitive to the degree of delamination between the concrete and the rebars. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool for health monitoring of concrete structures.