APPLIED MODELING FOR CORROSION PROTECTION DESIGN FOR MARINE BRIDGE SUBSTRUCTURES

Quantitative computational models have been developed to assist in predicting the course of corrosion-induced deterioration and the effect of corrosion protection models in reinforced concrete marine substructures. These models use the concept of a corrosion initiation stage (buildup of chloride ions until reaching a steel corrosion initiation threshold level) followed by a corrosion propagation stage (active corrosion leading to cracking and spalling of the concrete cover). Predictive models were applied to assess the reduction of corrosion rate by submerged and surface sacrificial anodes in marine piles. It was concluded that surface anodes located above water reduced corrosion significantly when the anode extended up to the top of the active steel zone. This predictive model was confirmed by parallel laboratory experiments with partially submerged piles and sacrificial anodes. Additional calculations applied the model to find the extent of cathodic protection feasible for partially submerged bridge footers with only submerged anodes. It was determined that useful protection may be obtained only when the concrete resistivity is very low. Modeling of the initiation stage of propagation resulted in the development of design derating factors to calculate the effect of diffusion geometries other than a flat wall (2- and 3-way corners, circular columns). Chloride ion binding by the concrete did not alter significantly the value of the derating factors, although it increased the time to corrosion initiation compared with a no-binding case. A final task of this work integrated the initiation and propagation phases of corrosion into a damage function model that predicts the amount of spalled area of a pile partially submerged in seawater as a function of service time. The quantitative formulation is suitable for selection of alternative corrosion protection strategies and incorporation in life cycle cost projection models.