Two and four–electrode configurations for contactless reinforced concrete corrosion monitoring

The paper addresses the need for a fast and reliable method for field monitoring reinforced concrete structures. A proof of concept is presented where a non-contact procedure provides quantitative information on the concrete resistivity and reinforcement corrosion rate. A Wenner-type probe is presented, where a combination of two and four-electrode measurements in a relatively high-frequency domain allows obtaining the information of interest. The method is based on the fact, verified by numerical simulations, that the embedded rebar works as an effective floating counter electrode and thus, for distances higher than a critical value (1 cm in the simulations done), the ratio of concrete resistivity to the measured impedance at 1 kHz is constant and only dependent on the electrode diameter. The apparent polarization resistance measured with the four-electrode arrangement and normalized to the concrete resistivity allows obtaining the actual polarization resistance without contacting the rebar whose distance to the electrodes shall be known.