Half-Cell Potential Mapping

Half-cell potential mapping is the standard electrochemical technique for assessing the probability of active reinforcement corrosion in concrete structures. TRSC uses this technique to determine where corrosion is actively occurring, where it is not, and where conditions are transitioning toward corrosion onset, information that directly informs the urgency and extent of remediation intervention.

The technique measures the electrical potential difference between embedded steel reinforcement and a reference electrode (copper/copper sulfate half-cell) placed on the concrete surface. More negative potential readings indicate a higher probability that the reinforcement at that location is actively corroding. ASTM C876 provides the standard interpretation criteria: potentials more negative than -350mV indicate a greater than 90% probability of active corrosion; potentials less negative than -200mV indicate a greater than 90% probability that corrosion is not occurring. The zone between these thresholds is classified as uncertain.

Half-cell potential mapping is performed on a systematic grid across the structure, producing a contour map that visualises the spatial distribution of corrosion probability. These maps are critical for proportionate remediation design, they show exactly where intervention is needed, where it is not, and where monitoring is the appropriate response. Without this data, remediation scope is typically based on visual damage plus a conservative margin, which frequently overestimates the extent of active corrosion.

At 12 Creek Street, half-cell potential mapping across the concrete facade demonstrated that corrosion activity was localised to specific zones rather than widespread, a finding that significantly reduced the scope and cost of the remediation programme. This is a typical outcome: half-cell mapping consistently demonstrates that the spatial extent of active corrosion is less than visual assessment alone would suggest.