Laboratory Validation of an Integrated Ground Penetrating Radar and Electrical Resistivity Tomography Framework for Reinforced Concrete Condition Assessment

This paper presents a laboratory-validated integrated assessment framework combining Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) for the non-destructive evaluation of reinforced concrete (RC) structures. A single RC beam specimen (3000 × 300 × 200 mm; C30/37, w/c = 0.50, CEM I 42.5N; 3 × T12 at 35 mm soffit cover) was subjected to four precisely controlled deterioration states: intact dry (Model A), water-filled crack (Model B), fully saturated (Model C), and chloride-induced active corrosion (Model D). Seven ERT datasets were acquired using a Wenner-Schlumberger array at electrode spacings of a = 7, 15, and 30 mm, and three 800 MHz GPR profiles were recorded for Models A, B, and C/D respectively. The ERT results demonstrate a systematic three-orders-of-magnitude decrease in median resistivity from the intact state (ρ₀ = 558 Ω·m) to the corroded condition (ρ = 10.6 Ω·m), with a depth-preferential low-resistivity distribution at rebar depth (z ≈ 24–48 mm; ρ < 10 Ω·m) providing partial discrimination between active corrosion and bulk moisture saturation. GPR analysis at 800 MHz confirms a reference wave velocity of v = 0.096 ± 0.008 m/ns by hyperbola fitting, localised 25–35% amplitude attenuation at the water-filled crack position, and pervasive 50–65% attenuation under saturated and corroded conditions. A four-stage integrated interpretation framework is validated against known ground-truth conditions: Stage 1 establishes local reference baselines (ρ₀, A₀); Stage 2 identifies anomalies against threshold criteria; Stage 3 cross-validates co-located GPR and ERT signatures; Stage 4 assigns risk categories 1–4. Explicit failure mode analysis identifies six conditions under which the framework is unreliable, most critically the moisture–corrosion ambiguity and the invisibility of dry cracks. The framework correctly classifies all four beam conditions and provides higher diagnostic confidence than either method applied independently.