A voltammetric study on the corrosion of prestressed steel in saturated Ca(OH)2 solution containing chloride ions

An electrochemical study of prestressed steel in saturated Ca(OH)(2) aqueous solutions (pH 12) was carried out in the absence and in the presence of chloride ions, in such a concentration that simulates the composition of seawater. Cyclic voltammetry, linear sweep voltammetry, open circuit potential transients, atomic absorption spectroscopy and scanning electron microscopy coupled to electron diffraction spectroscopy were employed. The linear polarisation curves analysis led to the determination of polarisation resistance, R (p), corrosion potential, E (corr), corrosion current density, j (corr) , Tafel slopes, breakdown potential, E (b) and repassivation potential E (repass). A linear dependence of the breakdown potential, E (b), on the square root of scan rate was obtained, according to the Point Defect Model (PDM). A crossover characteristic of the nucleation processes was observed in the presence of chloride ions. SEM/EDS studies revealed, as expected, a strong influence of the presence of chloride ions observed in the transpassive and the active regions. In conclusion, chloride ions contribute to enhance the corrosion of steel, most probably due to their adsorption on both the active and the passive electrode surfaces.