Investigation of the effect of water to cement ratio on the passive layer formed on carbon steel in cement paste

Purpose This paper aims to investigate the effect of the water-to-cement ratio on the passive layer forms of steel in cement paste. Design/methodology/approach Three sets of paste samples, each set containing three samples with a steel bar embedded in the center, were prepared using different W/C ratios of 0.35, 0.45 and 0.6, respectively. Electrochemical experiments, including Electrochemical impedance spectroscopy, linear polarization resistance and Mott-Schottky, were used to study the passive layer. Findings Results showed that increasing the water-to-cement ratio reduced corrosion current densities and shifted the corrosion potential to more positive values. Nonetheless, the passive layers formed in a lower water-to-cement ratio had fewer defects, suggesting higher stability. The thickness of the passive layer was inversely correlated with the water-to-cement ratio. It was hypothesized that the variations in the kinetics of oxygen reduction and the high alkalinity maintained at lower water-to-cement ratios were the reasons for such observations. Originality/value This paper for the first time, investigated the effect of water-to-cement ratio on passive layer.