Polarization behaviour of corrosion-resistant CTD reinforcing bars

THE POLARIZATION behaviour of some cold-twisted-deformed (CTD) reinforcing bars I has been studied by constructing Tafel plots. The study revealed that, in the presence of millscale on the rebar, the combined effect of the ratio of cathodic/anodic area to the amount of cold working will be reflected in the polarization behaviour. In view of this, the corrosion potential shifted substantially towards the active side with a high amount of cold twisting. In the case of rebar without millscale, the corrosion potential shifted significantly towards the noble side. The cathodic process was activation-controlled for the rebars having millscale and changed to diffusion-controlled when millscale was absent. The anodic process was dissolution of iron which depends on the available anodic area. However, the anodic current density as well as anodic Tafel slope will also depend upon the nature of the corrosion. Therefore, these were high when the corrosion was localized (which may be attributed to the local acidification process) in the untwisted rebar, and decreased substantially on cold twisting when millscale was removed and the nature of the corrosion changed to general.