Concrete Resistivity Mapping

Concrete resistivity is a measure of the concrete's ability to conduct electrical current, and therefore its ability to support the electrochemical corrosion process. Low-resistivity concrete (wet, chloride-contaminated, or highly porous) supports faster corrosion rates than high-resistivity concrete (dry, dense, well-cured). TRSC uses surface resistivity measurement as a rapid, non-destructive indicator of corrosion risk that directly complements half-cell potential mapping.

The measurement is performed using a four-point Wenner probe placed on the concrete surface. A small current is passed between the outer electrodes, and the voltage drop between the inner electrodes is measured. The apparent resistivity is calculated from the electrode spacing and the voltage-to-current ratio. Testing takes approximately 10 seconds per location, allowing rapid coverage of large structural areas.

Concrete resistivity provides information that half-cell potential mapping does not: it indicates the rate at which corrosion can proceed, not just whether corrosion is thermodynamically possible. A zone with active corrosion (high half-cell potential) but high resistivity will corrode slowly, potentially so slowly that intervention can be safely deferred. Conversely, a zone with active corrosion and low resistivity will corrode rapidly, requiring urgent attention. The combination of half-cell and resistivity data provides a complete corrosion risk picture.

TRSC interprets resistivity measurements using established threshold values: resistivity above 20 kΩ·cm indicates negligible corrosion risk regardless of chloride presence; 10–20 kΩ·cm indicates low to moderate risk; 5–10 kΩ·cm indicates high risk; below 5 kΩ·cm indicates very high corrosion risk. These thresholds are adjusted for concrete type, exposure conditions, and the specific corrosion mechanism under investigation.