Vertical impedance measurements provide significant quantitative information about the ability of concrete cover to slow the penetration of chloride ions that can corrode steel reinforcement in a bridge deck [1]. The primary limitations preventing the widespread adoption of vertical impedance for assessment of concrete bridge decks are (1) the necessity to have a direct electrical connection to the embedded steel reinforcement and (2) the low speeds of data acquisition. This work presents solutions to both limitations.
In previous work, our group developed a vertical impedance testing apparatus that was used to collect data from a continuously moving platform in the field [2]. While that apparatus greatly increased the speed of data collection, it required a direct electrical connection to the reinforcing steel; making a direct electrical connection to the rebar generally requires drilling through the concrete surface and tapping the reinforcing steel, which is a time-consuming process and therefore a major limitation to rapid data acquisition. In this work, a method using a large area electrode as a reference electrode for vertical impedance testing is proposed and validated using numerical finite-element simulations to demonstrate how a direct rebar connection can be eliminated. Based on these successful simulations, this work additionally reports how a large area electrode was constructed and incorporated in a continuously moving platform. When used in a multichannel arrangement, the use of a large area electrode allows rapid measurements of a full lane width of a bridge deck in a single pass. This development simplifies the entire vertical impedance testing process and greatly reduces the total time necessary to obtain measurements. Field data, including comparisons to direct electrical connections, demonstrate the utility of this technique and its general applicability to impedance-based measurements for quantitatively assessing the ability of the concrete cover to protect the reinforcing steel from corrosion
