What nondestructive testing (NDT) method is best suited for detecting internal voids in concrete bridge piers?

Ground Penetrating Radar (GPR) is the NDT method best suited for detecting internal voids in concrete bridge piers. GPR works by transmitting electromagnetic waves into the concrete and recording the reflected signals. When these waves encounter changes in material properties, such as the interface between concrete and an air-filled void, they are reflected back to the receiving antenna. The time it takes for the signal to return indicates the depth of the void, and the amplitude of the reflected signal indicates the size and nature of the void. GPR is effective because it can cover large areas relatively quickly and does not require direct contact with the concrete surface. Unlike other methods like ultrasonic testing, which may struggle with deep penetration in heavily reinforced concrete, GPR can often provide a clearer overall picture of subsurface conditions, making it ideal for detecting voids, honeycombing, and other internal anomalies in bridge piers.