Depassivation repair

The anodic process can be stopped by applying a coating to the reinforcement that acts as a physical barrier between the steel and the repair mortar. For this purpose only organic coatings, preferably epoxy based, should be used. Protection is entirely based on the barrier between the reinforcement and the mortar, and passivation of steel cannot be achieved because contact with alkaline repair material is prevented. This method should be used to protect depassivated areas of the reinforcement only as a last resort, i. e. when other techniques are not applicable and only for small specific applications [1,4]. It may be used, for instance, when the thickness of the concrete cover is very low and it is impossible to increase it to the proper level, so that the repair material cannot provide durable protection to the embedded steel. 

This is an S shaped curve that approximates to the two straight lines for To and in Figure 9.1. The curve could therefore be calculated if there are two sets of data. These can be derived from two sets of measurements of cracking, spalling and chloride content separated by several years, or taking one set of measurements at the present time and back calculating data for an earlier time This may be to the time of the first spall or a back calculation of the time to depassivation from the chloride profiles (approximately Tq). We can therefore derive values for A and B. These can be used to project forward the delamination rate and show how costs will escalate if work is deferred or how repair quantities will increase between the survey and the start of patch repair work. 

Film breaking it has been suggested that the passive film is continuously subjected to breakdown and repair (Vetter and Strehblow, 1970 Sato, 1971 Sato et al., 1971). The local breakdown events would be caused by mechanical stresses at defect sites or by electrostriction effects. In the absence of aggressive ions such as chloride, rapid repassivation takes place, whereas the presence of chloride could prevent repassivation of locally depassivated surfaces and thus cause pitting. This view of pitting considers that passivity breakdown itself is not caused by chloride, but is inherent to the nature of passive films. In this mechanism, adsorption on the passive film surface is not an important factor, but chloride adsorption on the metal surface remains a necessary step in the process of repassivation inhibition (and salt film formation). 

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