Zinc sacrificial anodes are not generally recommended to be used for the protection of steel in high
resistivity soils (> 1500 O.em) as the driving potential of the zinc will not be sufficient to provide the
required current needed to drive the structure to soil potential to the protection criterion of -850 mV
\V.Lt. CulCuS04. This criterion guarantees that the structure potential is shifted from the active region to
the immunity region of the potential-pH diagram, where the corrosion process is to be completely
halted. Generally, more than 300 mY of negative shift is required. Steel in concrete however, is in the
passive region due to the alkaline environment provided by the concrete surrounding which allows the
steel surface to develop a protective iron oxide film. Ingress of some species such as chloride ions leads
to the destruction of this protective film and pitting of the steel reinforcement initiates. Potential of the
steel in concrete is relatively less negative (generally <-200mV) especially if the film damaging species
have not reached the steel/concrete interface.