The importance of geometrical considerations in the measurement of steel corrosion in concrete by means of AC impedance

The measurement of electrochemical impedance is widely used not only for corrosion studies, but also for studying a high variety of electrochemical processes. Either two electrode or three electrode systems are used in very different arrangements in these measurements. In the present paper, some results and comments are presented on how different geometrical dispositions of the electrodes may affect the results so much, which is one of the reasons that makes the comparison between them more difficult. It is well known that the capacitance is electrode-geometry-dependent, as is the electrical resistance. Therefore, the distance between the electrodes and their size and location in the cell will affect the characteristic frequency response. As in the case of inert capacitors, only well defined geometrical arrangements will enable the calculation of comparable capacitance values when the study of the concrete is attempted.