In addition to a negative potential shift, a cathodic current induces a number of other important effects which protect steel in concrete. In the present work, the chloride barrier and extraction properties of the electric field were used to provide a basis for the choice of the design current density. Its value was then determined by the concrete resistivity, chloride content, and separation between the anode and the cathode. In many cases, the values derived will be similar to those used in practice. However, high protection current densities were predicted for steel in heavily chloride contaminated concrete of low resistivity and small cover. To assess the performance of a cathodic protection system, it is suggested that the voltage drop induced in the concrete, variations in the applied current density, the removal of chloride ions from the vicinity of the steel, and a measure of the steel potential shift achieved could be monitored. The potential shift and local current density may be used to give an indication of the unpolarised steel corrosion rate and, thus, the achievement of passive conditions.
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