Non‐destructive determination of the sheet resistance of conductive coating anodes on concrete

Abstract

Conductive coatings form the basis of a common anode system used in the cathodic protection of steel in concrete. One of the properties required by such a coating is a low sheet resistance (square resistance). This, together with the protection current density and anode connection geometry, determines the uniformity of the current distribution over the concrete surface. It is shown that the sheet resistance may be determined using a non‐destructive test employing a collinear four‐probe array. When a current (I), passed between the outer probes of an equally spaced four‐probe array, induces a voltage difference (δV) between the inner probes, the sheet resistance is given by (pgr;/ln2)x(dgr;V/I). The validity of the measured values may be assessed by the absence of any sensitivity to probe orientation and spacing. This technique may be used in the assessment of the quality of installed conductive coating anodes. The sheet resistance will depend on factors such as the thickness and age of the installed coating.