Detecting steel bars and discontinuities in reinforced concrete members using gamma rays

Reinforced concrete is a non-uniform, complex material. Current nondestructive testing (NDT) techniques, such as impact/echo testing, are unable to accurately locate or determine the size of steel reinforcement bars and various discontinuities in reinforced concrete members. This article describes a testing technique using penetrating gamma rays to obtain images of steel bars, cracks and holes within reinforced concrete members. The geometry of the projected image is used to determine the size and location of steel bars and discontinuities, and to measure cover depth. Further, an exposure curve is developed to better understand the relationships between radioactive source strength, thickness of the reinforced concrete and exposure time. The accuracy of the present technique is validated through experiments, making it useful for evaluating the safety of reinforced concrete structures.