Deconvolution of the Partial Anodic and Cathodic Processes during the Corrosion of Carbon Steel in Concrete Pore Solution under Simulated Anoxic Conditions

A mixed potential model has been developed to deconvolve the negative total current density that is observed at potentials more negative than the open circuit potential, E-corr, during potentiostatic polarization of carbon steel in the simulated concrete pore solution under anoxic conditions into its partial anodic and cathodic components as a function of potential across the passive range. Deconvolution was successfully achieved by optimizing a Mixed Potential Model (MPM) comprising the Point Defect Model (PDM) to describe the partial anodic process and the Generalized Butler-Volmer equation to describe the partial cathodic process of hydrogen evolution. In this manner, the corrosion rate can be determined across the entire passive range, including the range of potential (E < E-corr) within which the net observed current density is negative. It is found that the corrosion rate increases significantly when the potential is lowered below a certain value, possibly due to the change of the oxidation state of iron within the outer-layer of the film. (C) 2014 Elsevier Ltd. All rights reserved.