A Comparison Between GPR and Ultrasonic Techniques for VOID Detection Beneath Reinforced Concrete Sections

This study provides practical users with a systematic comparative study GPR and Ultrasonics as applied to the detection and location of voids beneath steel-reinforced concrete sections. Complementary surveys were collected across a 0.3m-thick, steel-reinforced concrete test ‘slab’ that covered a sub-metre scaled target void buried in the underlying clayey soils. To make the study as realistic as possible, and ensure data compatibility, the surveys were collected ‘blind’ (i.e., without a detailed a priori knowledge of the target depths and/or sub-surface conditions) and across the same survey grid. The 2D and 3D results (sections and time-slices) show that despite the relative popularity of GPR, ultrasonic methods can perform equally well for this type of specific investigation scenario and have shown the potential for overcoming some of the inherent limitations of GPR when faced with dense, complex rebar meshes.