Electrochemical characterization of mild steel in alkaline solutions simulating concrete environment

•The electrochemical behavior of mild steel was investigated in sat.Ca(OH)2 solution.•Cyclovoltammetries pointed out the double step nature of steel passivation process.•Fe(II) formation reaction is predominant in the onset of the passive condition.•Three days of immersion are required to stabilize the response of the passive film.

The majority of the studies on corrosion mechanism and protection of reinforcing steel bars are performed in alkaline solutions simulating the concrete environment, thus avoiding the complications related to the preparation of representative reinforced concrete samples. In this work the electrochemical behavior of B450C mild steel was studied in saturated Ca(OH)2 solution by cyclicvoltammetry. Comparison with the electrochemical response in 1 M NaOH was also carried out, being such electrolyte the most commonly used for iron passivation studies. Results confirm the coexistence of two main processes, one leading to Fe(OH)2 and the following (reversible) to Fe(III) oxo-hydroxides. The latter appears more relevant to the growth of a protective layer and in turn strictly connected to the operative condition of the cyclic voltammetry. The influence that time has on the passive film growth was then investigated by means of anodic polarization and electrochemical impedance spectroscopy. All the results indicated that at least three days of immersion in Ca(OH)2 are required to guarantee the stabilization of the electrochemical response, thus leading to a protection similar to that observed with reinforced concrete.