Ground-Penetrating Radar Evaluation for Detecting Subsurface Defects in Reinforced Concrete Slabs through Controlled Laboratory Investigation

Ground-penetrating radar (GPR) was experimentally evaluated as a nondestructive testing (NDT) technique for detecting and characterizing subsurface defects in reinforced concrete (RC) slabs representative of bridge deck deterioration. Five laboratory specimens were fabricated with controlled defect types, including corrosion, delamination, honeycombing, and voids, to enable quantitative validation of detection capability. Dielectric calibration confirmed consistent material properties among slabs, and environmental variations in temperature and humidity had minimal influence on signal response under controlled conditions. Scans performed after 28 days of curing produced clear, interpretable radargrams, whereas early-age scans (7–14 days) showed signal attenuation and scattering owing to elevated moisture content and dielectric instability. Distinct radar signatures were identified for each defect type, including narrow hyperbolic reflections for rebars, flattened hyperbolas for voids, and horizontally oriented strip patterns for delamination. Quantitative analysis indicated an average depth deviation of 0.15 in. and approximately 80% accuracy in delamination thickness estimation. Detection sensitivity decreased for defects smaller than 8 in. or spaced closer than 2 in., where overlapping reflections limited lateral resolution. The findings establish practical detection thresholds and confirm that, when properly calibrated and applied under stable dielectric conditions, GPR provides a reliable method for identifying and sizing subsurface defects in RC, while highlighting limitations associated with closely spaced anomalies and structural complexity.