Rebar corrosion assessment using polarimetric ground penetrating radar

Ground Penetrating Radar (GPR) has been widely used for non-destructive testing to detect reinforcing bars (rebars) in concrete. However, the mechanism-level interpretation and quantitative characterization of GPR responses from corroded rebars remain at an early stage. Existing single-polarization GPR approaches mainly rely on echo amplitude and time-delay features to infer corrosion, yet these responses are highly sensitive to experimental conditions and environmental factors, leading to inconsistent trends [1]. With the advancement of polarimetric GPR, increasing attention has been paid to leveraging polarization information for rebar corrosion detection [2]. Nevertheless, existing polarimetric power decomposition methods often classify rebar returns as being dominated by surface scattering, whereas rebars exhibit a typical linear geometry and should theoretically present a pronounced dipole-scattering component.To address this issue, we propose a four-component polarimetric decomposition method for rebar scattering characterization and corrosion-state evaluation. Building upon the Dey three-component decomposition [3] and inspired by the Huynen decomposition [4], the proposed method uses the real part of T12, i.e.,  R{T12} as a key indicator of dipole scattering. This term can be interpreted as a shape-related indicator that tends to be pronounced for line-like targets, enabling a physically interpretable decomposition of the total scattering power into four components: surface scattering, double-bounce scattering, volume scattering, and dipole scattering.Experiments were conducted using a VNA-based full-polarimetric GPR system equipped with dual-polarized Vivaldi antennas operating from 0.7 to 6 GHz. Reinforced concrete specimens with a 12 mm diameter rebar and a 50 mm concrete cover were tested under an indoor accelerated corrosion setup over 20 days. For each corrosion day, the scattering powers of the four components were computed and normalized, and the mean values were extracted within a region of interest (ROI) centered on the rebar response. The decomposition results indicate that the rebar scattering is primarily governed by dipole and surface scattering. Moreover, the temporal evolution of the decomposed powers over the corrosion period reveals that the dipole scattering power is more sensitive to corrosion progression than the surface scattering component, suggesting it as an effective feature for evaluating corrosion stage and tracking corrosion development.References[1] Faris N, Zayed T, Abdelkader E M, et al. Corrosion assessment using ground penetrating radar in reinforced concrete structures: Influential factors and analysis methods[J]. Automation in Construction, 2023, 156: 105130.[2] Liu H, Zhong J, Ding F, et al. Detection of early-stage rebar corrosion using a polarimetric ground penetrating radar system[J]. Construction and Building Materials, 2022, 317: 125768.[3] Dey S, Bhattacharya A, Ratha D, et al. Target Characterization and Scattering Power Decomposition for Full and Compact Polarimetric SAR Data[J]. IEEE Transactions on Geoscience and Remote Sensing, 2021, 59(5): 3981-3998. DOI:10.1109/TGRS.2020.3010840.[4] Huynen J R. Stokes matrix parameters and their interpretation in terms of physical target properties[C]//Polarimetry: Radar, infrared, visible, ultraviolet, and X-ray. SPIE, 1990, 1317: 195-207.