The Effect of Chloride Depletion on the Corrosion State of Steel in Alkaline Environment

In the recent literature the efficiency of Cathodic Protection (CP) of steel in concrete is frequently discussed with respect to comparatively small protection currents and often observable potential ennoblement of open circuit potentials (EOC), which are generally explained by repassivation effects occurring during CP. Cathodic polarisation causes chemical alterations at the steel concrete interface, which are beneficial concerning the corrosiveness of the environment. Due to forcing the cathodic partial reaction, the hydroxide ion concentration at the steel surface increases. The applied electric field additionally causes the migration of chlorides to the external anode. The investigations discussed in this paper aim to clarify to which extent the migration of chlorides have impact on repassivation of reinforcement. On the basis of the data obtained, a FEM-model is proposed to calculate the time and voltage-depending migration of chloride ions in consequence of electric fields as applied in CP of steel in concrete.