Modeling the Effect of Mill Scale on the Local Depassivation of Steel Rebar In Concrete

Corrosion of rebar in concrete is one of the most prominent durability problems in reinforced concrete, especially where de-icing or seawater salts come into contact with the structures. Previous electrochemical and microscopic investigations have shown that local crevices between the mill scale and the underlying steel surface accelerate the depassivation of rebar in concrete.  Steel depassivation in concrete depends highly on the chloride-to-hydroxide ratio of the pore solution. The differential equations for the transport of hydroxide, chloride and seven other ionic species in the concrete pore solution, coupled with the electrochemical reactions on the steel surface, were numerically modeled in simulated crevices that exist between the mill scale and the steel surface using the finite element technique.  The implications of the depassivation of steel in concrete will be discussed.