Detection of subsurface defects in concrete slabs using ground penetrating radar

Abstract

The use of Ground Penetrating Radar (GPR) in the Non-Destructive Evaluation (NDE) of structures has significantly increased in the past decades. Several attempts have been made by the researchers to detect the surface and subsurface deterioration of the concrete using GPR. This study aims to analyze the attenuation of the signal in concrete due to various subsurface defect and rebars, simulated in a controlled laboratory environment. Three small plain concrete slabs of surface dimensions of 25 x 50 cm and varying depths of 5 cm, 10 cm, and 20 cm were utilized in this study. The slabs were scanned using a GPR by stacking the slabs one above another to simulate different depths for the detection of the gap between the concrete slabs. Materials such as paper sheets, cardboard sheets, foam sheets, reinforcement bars, and an FRP (Fiber Reinforced Polymer) bar were placed between the concrete slab, and the reflections amplitudes were investigated at the interface medium. An air gap and water gap are introduced between the slabs to simulate defects between slabs which is typically the case for horizontal cracks and delamination. The results obtained are promising as they show a variation in the measured reflected amplitudes for different materials across all depths. This research will be helpful to detect subsurface cracks on the actual structures such as concrete bridge deck and its standardized quantification could be useful to the decision-makers for the monitoring as well as planning the repair and retrofitting of the structures.