POLARIZATION CURRENT DISTRIBUTION AND ELECTROCHEMICAL IMPEDANCE RESPONSE OF REINFORCED-CONCRETE WHEN USING GUARD RING ELECTRODES

The electrochemical impedance response of reinforced concrete is complicated by the presence of extended corrosion macrocells and the relatively high resistance of the electrolytic medium. Guard ring electrodes are used in an attempt to confine the excitation current so that the reinforcing steel area sampled by the measurement is well defined. In order to better understand the application of guard electrodes, a simplified system has been analyzed by numerical modeling to address the relative distribution of ac current over the rebar for representative situations. The difference between actual corrosion current and EIS-evaluated value is computed for each case, with emphasis on quantitative factors affecting measurement error.