Non-Contact Measurement to Detect Steel Rebar Corrosion in Reinforced Concrete by Electrochemical Impedance Spectroscopy

Non-contact wide-frequency-range electrochemical impedance measurements were employed to detect the corrosion of a steel rebar embedded into concrete. The measurements were performed by placing two Cu sensing electrodes at a distance of 50 mm from each other on the concrete surface immediately above corroded and non-corroded rebar portions. The low-frequency impedance related to the steel rebar/concrete interface was found to be lower in the former case, leading to the detection of corroded portions of steel rebar embedded in concrete. Such discrimination was only possible at cover thicknesses of up to 50 mm (cf. inter-electrode distance), as at higher thicknesses, a large fraction of current flowed directly from one electrode to the other one. This demonstrates the importance of selecting the proper distance between the sensing electrodes for optimal detection of corrosion portions when the cover thickness of reinforced concrete is known.