(Invited) Electrochemical Impedance Spectroscopy of Reinforced Concrete
Authors: Alexander Christopher Lewis 
Published: December 2024

Electrochemical impedance spectroscopy (EIS) is an effective method for assessing interfacial parameters within systems that have consistent electrode-electrolyte interface impedance and for which a uniform distribution of current can be acheived. The application of EIS to reinforced concrete presents a myriad of challenges due to various factors such as moisture content, interfacial porosity, and the presence of corrosion products. These complexities make it imperative to clearly define the limitations in the application of EIS to corrosion assessment of steel in concrete. The impedance response may include multiple time constants, forming a Nyquist display comprising capacitive loops with various degrees of depression and overlap. Despite numerous proposed models1,2,3 attempting to account for these responses, there is a lack of widely adopted models capable of characterizing the steel-concrete interface across different stages of corrosion. Complicating matters further, early corrosion stages are often nonuniform, making it difficult to discern whether the observed multiple time constants reflect processes occurring uniformly across the surface or at distinct locations along it. In the first part of the presentation, the challenges associated with analyzing the impedance of steel within concrete will be described, including an in-depth exploration of factors such as geometry-induced frequency dispersion and the influence of localized forms of corrosion on impedance responses.4

The second part of the presentation will explore the use of bipolar electrochemical impedance spectroscopy (BPEIS) as a potential solution for field applications of corrosion assessment where direct electrical contact with the reinforcement may not be feasible. BPEIS is a non-contact method of which an electrically conductive material within an electrolyte is indirectly polarized with the goal of probing the interfacial impedance of the embedded material.5 An application example of monitoring of corrosion in post-tensioned tendons will be provided to validate the efficacy of BPEIS in evaluating corrosion rate and changes in cementitious material resistivity. Despite the challenges associated with isolating the true interface impedance, the method demonstrates reliability in assessing the corrosion state of the embedded reinforcement.

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