Effect of Moisture on the Spatial Uniformity of Cathodic Protection of Steel in Reinforced Concrete

Abstract A numerical model for the cathodic protection (CP) of steel in reinforced concrete was developed. Parameters were set to represent a three-dimensional section of a bridge beam exposed to the atmosphere and coated with a thermally sprayed zinc anode. Both the diffusion of oxygen and the conduction of charge within the concrete were considered explicitly through a two-dimensional finite element model. The diffusivity and conductivity were represented as functions of concrete moisture content. Electrochemical reactions considered at the rebar-concrete interface included the reduction of oxygen, the oxidation of iron, and the evolution of hydrogen in a constant-potential CP circuit. Reaction-kinetic parameters for actively corroding steel (not passivated steel) were used. Reactions at the zinc-concrete interface were not considered explicitly. The effectiveness of protection was found to vary significantly with both concrete moisture content and position on the rebar. For spatially uniform pore satur...