Patch repair technology with sacrificial zinc anodes in RC slabs with corroded steel bars

Abstract

Concrete spalling is one of the most common types of damage encountered in RC structures. Concrete spalling is caused by corrosion of steel reinforcement within the RC due to carbonation and/or chloride contamination. A simple patch repair work is a common technique used to reapply concrete at spalling area. However, cracks within the concrete would start to form within a month after the application of patch repair. This is because the application of patch repair inadvertently introduces an additional corrosion mechanism. Steel reinforcement corrosion can be significantly reduced by implementing sacrificial anodes which are made from less noble materials than steel reinforcement to divert majority of corrosion activity to the anodes. In this study, the effect of zinc sacrificial anodes to RC slabs with patch repair work was studied. The microcell and macrocell corrosion of both the steel reinforcement and zinc sacrificial anodes within four RC slabs with different sacrificial anode arrangements were measured to determine the most effective arrangement of zinc sacrificial anodes in protecting the steel reinforcement. Two RC slabs have sacrificial anodes installed in the patch work area with one slab having a single 300 mm × 50 mm × 10 mm zinc plate placed in the centre of the patch work, while the other slab having twelve 25 mm × 50 mm × 10 mm zinc plates spread evenly within the patch work. The last RC slab would have twelve 25 mm × 50 mm × 10 mm zinc plates installed within the corroded area surrounding the patch work area. Linear Polarisation Resistance and Galvanic Coupling were techniques used to measure the magnitude of microcell and macrocell corrosion current density, respectively. It was found out that patch repair mix applied to RC slabs lowers corrosion potential value. Subsequently, the corrosion potential difference between steel reinforcement outside and within the patch area increases and thus induces an additional macrocell corrosion. Furthermore, the highest amount of macrocell corrosion can be encountered at steel segments near the patch repair area. Compared with each sample, it was discovered that zinc sacrificial anodes installed within areas with high level of chloride contamination provided the best protection for the steel reinforcement against corrosion damage.