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

Master Thesis


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Reinforcement corrosion is the largest contributor to the deterioration of existing RC structures worldwide. The aggressive electrochemical process causes destruction to the steel by a loss in cross section and rib height, which in turn affects the bond between steel and concrete and consequently the structural performance of reinforced concrete structures. During a repair strategy, when the patch repair method is considered, one of the steps usually involves the application of a protective coating to the corroded and subsequently cleaned steel. It is well accepted that protective coatings offer corrosion resistance to the steel in reinforced concrete repaired elements. However, information on how well the coated rebar bonds to the new surrounding repair concrete is limited. Hence, developing an understanding on the bond performance of repaired coated rebar is important for engineers in the construction repair industry. One commercially available epoxy-modified, cementitious coating material was considered in this study, Sika ® Armatec ® -110- EpoCem, and applied with one or two coats of 0.6 mm each. Rebar corrosion damage levels of 0%, 10% and 20% (of steel mass loss) were simulated by mechanical grinding of sound rebar samples, attempting to represent the condition of cleaned corroded rebar. Two steel bars, Y12 and Y16, of different diameters were considered. 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, referred to as C45, M45 and M65, respectively. Pull-out testing was conducted on a total of 108 specimens to assess the effect of coating thickness on the bond with respect to the different parameters of this study. The results indicate that the w/b ratio of the mortars had a significant influence on the bond and the addition of stone showed no difference on the failure loads obtained. There was no significant effect of the rebar diameter on the pull-out force for uncorroded rebar, although with cleaned corroded rebar the effect was significant. Specimens with 10% mass loss had larger reductions in pull-out force compared to those with 20% mass loss. While coatings reduced the bond of uncorroded and cleaned corroded rebar, the thickness of the coating had practically no influence on the pull-out force. Using C45-12 with two coats on 20% corroded steel, the pull-out force was 80% compared to before corrosion. Failure of uncorroded specimens was dominated by splitting, and slip was mostly seen for cleaned corroded specimens. With coatings applied to uncorroded bars, slip coating failure was evident with uncorroded steel while splitting with coating failure was evident especially with Y16. From the corroded coated specimens, there appeared to be good contact between the cleaned corroded steel and repair material.