Multiple Corrosion Protection Systems for Reinforced Concrete Bridge Components [2007]

Federal Highway Administration2007PDFTech ReportDarwin, DavidBrowning, JoAnnLocke, Carl E.Nguyen, Trung V.University of Kansas. Center for ResearchUnited States. Federal Highway Administration. Office of Infrastructure Research and DevelopmentTurner-Fairbank Highway Research CenterUnited StatesCorrosion resistant materialsReinforced concreteCorrosion protectionConcrete bridgesCorrosion resistant materialsReinforced concrete--Corrosion--PreventionConcrete bridges--Corrosion--PreventionFHWA-HRT-07-043DTFH61-03-C-00131Interim report; Sept. 2003-Mar. 2006.Eleven systems combining epoxy-coated reinforcement with another corrosion protection system are evaluated using the rapid macrocell, Southern Exposure, cracked beam, and linear polarization resistance tests. The systems include bars that are pretreated with zinc chromate to improve the adhesion between the epoxy and the reinforcing steel; two epoxies with improved adhesion to the reinforcing steel; one inorganic corrosion inhibitor, calcium nitrite; two organic corrosion inhibitors; an epoxy-coated bar with a primer containing microencapsulated calcium nitrite; the three epoxy-coated bars with improved adhesion combined with the corrosion inhibitor calcium nitrite; and multiple coated bars with an initial 50-\u3bcm (2-mil) coating of 98 percent zinc and 2 percent aluminum followed by a conventional epoxy-coating. The systems are compared with conventional uncoated reinforcement and conventional epoxy-coated reinforcement. The results presented in this report represent the findings obtained during the first half of a 5-year study that includes longer-term ASTM G 109 and field tests. In the short-term tests used to date, the epoxy-coatings evaluated provide superior corrosion protection to the reinforcing steel. The results also indicate that the bars will continue to perform well in the longer term, although the tests do not evaluate the effects of long-term reductions in the bond between the epoxy and the reinforcing steel. The corrosion rate on the exposed regions of damaged epoxy-coated reinforcement is somewhat higher than the average corrosion rate on the surface of uncoated reinforcement subjected to similar exposure conditions. The use of concrete with a reduced water-cement ratio improves the corrosion performance of both conventional and epoxy-coated reinforcement in uncracked concrete but has little effect in cracked concrete. Increased adhesion between the epoxy and reinforcing steel provides no significant improvement in the corrosion resistance of epoxy-coated reinforcement. It appears that corrosion inhibitors in concrete and the primer coating containing microencapsulated calcium nitrite improve the corrosion resistance of the epoxy-coated steel in uncracked concrete, but not in cracked concrete. The zinc coating on the multiple coated bars acts as a sacrificial barrier and provides some corrosion protection to the underlying steel in both uncracked and cracked concrete. The degree of protection, however, cannot be evaluated based on the results available to date.96