Evaluation of Multiple Corrosion Protection Systems for Reinforced Concrete Bridge Decks

Abstract

Chloride-induced corrosion is one of the leading causes of premature serviceability failure in reinforced concrete bridge decks. In an effort to mitigate the effect of corrosion on the longevity of concrete bridge decks, several corrosion protection systems have been developed. The current study evaluates the effectiveness of multiple corrosion protection strategies when used in conjunction with epoxy-coated reinforcement (ECR). The epoxy coating in all test bars is penetrated with either four or ten 3-mm (1/8-in.) diameter holes. The systems evaluated include three corrosion inhibitors (DCI-S, Rheocrete 222+, and Hycrete DSS) in concrete with a w/c ratio of 0.45 and 0.35, an ECR containing a primer of microencapsulated calcium nitrite between the epoxy and the steel in concrete with a w/c ratio of 0.45 and 0.35, three types of increased adhesion ECR (ECR pretreated with chromate prior to the application of the epoxy coating, and ECR with increased adhesion epoxies developed by DuPont and Valspar) evaluated in concrete with a w/c ratio of 0.45, as well as in concrete containing DCI-S corrosion inhibitor, and multiple-coated reinforcement that contains a zinc layer between the steel and the DuPont 8-2739 epoxy coating in concrete with a w/c ratio of 0.45. Conventional steel and epoxy-coated reinforcement serve as control specimens; the performance of the epoxy-coated reinforcement is compared to the performance of the conventional steel reinforcement. Each corrosion protection system is evaluated using the Southern Exposure and cracked beam tests. Macrocell and microcell corrosion losses, mat-to-mat resistances, top and bottom mat corrosion potentials, and critical chloride concentrations are measured during the test. Upon completion of the study, each specimen is autopsied and any disbondment of the epoxy coating from the steel is measured. Of the systems evaluated in this study, conventional steel exhibits the greatest amount of corrosion. ECR, whether in uncracked or cracked concrete, exhibits low corrosion losses; well below the magnitude required to cause corrosion-induced surface deterioration. A lower w/c ratio provides additional protection in uncracked concrete, but affords little to no protection in cracked concrete. Corrosion inhibitors, while effective in uncracked concrete, afford no additional protection against corrosion in cracked concrete. All three improved adhesion ECR systems exhibit corrosion performance that is similar to conventional ECR. Multiple-coated reinforcement exhibits greater corrosion losses than conventional ECR, but the corrosion losses are below the magnitude of corrosion loss required to cause corrosion-induced surface deterioration. The effective critical chloride threshold for epoxy-coated reinforcement is several times higher than that of conventional reinforcement. A relationship exists between microcell and macrocell corrosion loss, and between both microcell and macrocell corrosion loss and the disbonded area of epoxy observed on the bar. The cathodic disbondment test (ASTM A775) does not appear to be a reliable indicator of corrosion disbondment performance of in-service epoxy-coated reinforcement.