Chloride-Induced Depassivation of Steel in Concrete-Influence of Electrochemical Potential and Anodic Polarization Level

Exploring the depassivation process of reinforcing steel in concrete and the chloride threshold level (CTL) is a major research challenge. The depassivation process is influenced by a wide variety of parameters. One of these is the steel potential, more precisely its spatial distribution, its variations and the resulting differences and polarization states. For certain electrochemical test methods sometimes an external polarization is applied, but the influence on naturally ongoing processes like the depassivation of the steel has remained largely unexplored. When determining the time of depassivation of reinforcing steel, in conjunction with determining the CTL, the application of an external anodic polarization is an established test setup. At the Institute of Building Materials Research (ibac) of the RWTH Aachen University the effect of external anodic polarization to different levels on the time to depassivation and on the CTL is explored. The current investigations show that there is no clear effect on the depassivation behavior for anodic polarizations up to +550 mV versus free rest potential in the passive state.