CP Criteria for Reinforced Concrete in Marine Exposure Zones

Abstract

A marine environment may be characterized by tidal, submerged, and atmospherically exposed zones. Cathodic protection (CP) of reinforced concrete in the submerged zone may induce reducing conditions associated with immunity to corrosion characterized by negative steel potentials. In the atmospheric zone CP induces an improvement in the local environment at the steel, promoting steel passivity, which may be monitored using a potential decay criterion in relatively dry conditions. Many protective effects will persist following the interruption of the current, providing a basis for intermittent CP in the tidal zone. However, conventional criteria may not be reliable in this case. The importance of the current-induced improvement in the tidal zone environment provides justification for the use of a protection current density criterion. The integrated current densities required to arrest high initial corrosion rates are relatively low. Protection criteria may also be based on a positive trend in measured potentials indicative of passivating steel and the induced voltage drop through the concrete cover that drives the removal of chloride ions and sustains a high hydroxyl concentration gradient between the steel and the external environment.