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08055 Can Zinc Prevent Corrosion of Pre-Stressed Concrete Cylinder Pipe in High Resistivity Soils?

Product Number: 51300-08055-SG
ISBN: 08055 2008 CP
Author: Faraj A. Garman
Publication Date: 2008
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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.
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.
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