Electrochemical Modeling of Passive Film Formation on Steel in Simulated Concrete Pore Solutions

H.M. Bernardes[1], M. Mancio[2], and P.J.M. Monteiro[2]
[1]São Paulo State University, Ilha Solteira, SP, Brazil
[2]University of California, Berkeley, CA, USA

In this work, a tridimensional model of the electrochemical reactions taking place on the alloy/solution interface has been developed in the COMSOL Multiphysics environment. The model accounts for solution chemistry, cell potential, and solves the related mass, momentum and energy balances. The simulation is based mainly on the experimental results obtained by Mancio et al, which have employed in-situ Electrochemical Surface-Enhanced Raman Spectroscopy to characterize the passive films formed on steel under different conditions. We expect that the model will help elucidate the dynamics of passive film formation and particularly breakdown as a function of pH drop and chloride ion concentration, the two main causes of corrosion initiation in concrete structures. The study indicates that important passive film characteristics such as composition, protectiveness and thickness vary considerably depending on solution pH and ionic strength.