Chloride threshold dependence of pitting potential of reinforcements

Chloride threshold is one of the key parameters needed for service life prediction of concrete structures. The main difficulty that the determination of this parameter encounters is that the chloride threshold inducing active corrosion is not a unique value and depends on several variables. Among them the electrical potential exhibited by the rebar surface is the one less experimentally studied, even though it was identified some decades ago as the most comprehensive controlling parameter for the disruption of passivity. In the present paper the influence of the potential of reinforcements embedded in mortar on the chloride threshold has been studied for the first time in a region from +250 to -650 mV with respect to SCE. Identical samples have been tested in order to perform a statistical treatment and so mean values are given. The chloride thresholds found are expressed as total and free chloride as well as chloride/hydroxide (Cl-/OH-) ratio. The results show that chloride threshold is independent of the potential for values more anodic than -200+/-50 mV (SCE) being this region the typical potentials exhibited by passive reinforcements in atmospheric conditions. For potentials more cathodic than -200+/-50 mV (SCE), the threshold progressively increases and a linear fitting is possible. The dependence of chloride threshold with the potential approaches to the understanding why in previous works researchers have found significant differences. (C) 2002 Elsevier Science Ltd. All rights reserved.