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.