Addressing geometric influences on electrochemical impedance spectroscopy for accurate corrosion assessment in steel-reinforced concrete beams

Electrochemical impedance spectroscopy (EIS) is widely employed in laboratory investigations of steel corrosion in concrete. However, the complex geometry of reinforced concrete specimens presents significant challenges due to nonuniform current distributions, leading to frequency dispersion in the impedance response. This study explores the influence of specimen geometry on the impedance response of steel in concrete, focusing on the effects of current distribution and the resulting frequency dispersion.

A finite element model was developed to simulate the impedance response of singly reinforced concrete beam specimens, revealing key insights into the geometric factors that contribute to frequency dispersion. A characteristic length is defined for cases where the beam length exceeds that of the counter electrode, allowing determination of the frequencies influenced by the geometry induced dispersion. Evidence is presented to suggest that frequency dispersion may not be avoidable considering the typical resistivity range of concrete.

To address this issue, a mathematical expression is described that relates the apparent polarization resistance to the true polarization resistance by accounting for geometric factors and concrete resistivity. Recommendations are also provided for minimizing the effects of geometry-induced frequency dispersion in laboratory measurements, particularly by optimizing specimen geometry.