A Concrete Resistivity Method Based on a Simple Measuring Cell for Onsite Corrosion Monitoring: Study on Concrete Under Varying Conditions

Concrete resistivity ( ρ ) is commonly monitored in situ using sensors based on the rebar‐disc (RDM) or four‐electrode (FEM) methods. This study validates, for the first time in reinforced concrete, an innovative corrosion sensor approach (CSA) previously tested only in simulated pore solutions. The CSA uses a single embedded two‐electrode sensor that also allows the corrosion rate, offering a significant advantage for structural health monitoring. CSA resistivity values were broadly consistent with those from established reference methods: 2.9% higher than the RDM and 20% lower than the two‐electrode method. Larger differences were observed with the FEM, decreasing when a finite‐element cell factor (103%) was applied instead of one for semi‐infinite elements (208%). This trend aligns with expected differences between FEM surface resistivity and bulk values. Additionally, a simple correction factor is proposed to normalise ρ to the reference temperature ( T ) of 20°C, expressed as 1 /( a· exp(( b )· T )), with a and b equal to 1.7251 and 0.027 for low‐resistivity concretes and 2.4851 and 0.046 for medium‐ to high‐resistivity concretes. A general model for the full resistivity range yielded a = 2.0687 and b = 0.036. While further research is needed to explore wider corrosion scenarios, the results highlight the potential of the CSA as a practical tool for both laboratory and in situ corrosion assessment.