Investigating the effects of anti-corrosive coatings on the bond between corrosion-damaged rebar and concrete repair materials

Abstract

Reinforcement corrosion causes destruction to the steel by a loss in cross section and rib height, which can affect the bond between steel and concrete. During repair of corrosion-damaged reinforced concrete members, a protective coating is usually applied to the cleaned corroded steel. There is, however, little information available on the bond performance of repair coatings. Furthermore, the effect of their coating thickness and other parameters like rebar diameter, corrosion degree and repair material properties are not well understood when considered in parallel with repair coatings. This paper seeks to contribute towards understanding the use of anti-corrosive coatings and the influence of their thickness on the bond between cleaned steel reinforcement and repair materials, when used in combination with different bar geometries at varying degrees of corrosion damage. In this investigation, two high tensile steel bars, Y12 and Y16, were considered. Rebar corrosion damage levels of 0%, 10% and 20% (of steel mass loss) were simulated by mechanical grinding of sound rebar samples to represent the condition of cleaned corroded rebar. A commercially available epoxy-modified, cementitious coating material was applied to the steel in one or two coats, with each coat being 0.6 mm thick. Three repair materials with CEM I 52.5N were considered in this study, which included one concrete with a w/b ratio of 0.45 and two mortars with w/b ratios of 0.47 and 0.65. Pull-out testing was conducted on 108 specimens, and the results analysed by means of the one-way ANOVA test to assess the effect of mainly coatings and other parameters on the bond. The results indicate applying coatings to 10% and 20% corroded steel does not significantly reduce the bond for the M65 and C45 mixes. Furthermore, the difference between one and two coats had little influence on the bond of corroded steel for all rebar geometries and repair mixes.