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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
REPORT |
This report is an archived publication and may contain dated technical, contact, and link information |
Publication Number: FHWA-HRT-11-060 Date: November 2011 |
Publication Number: FHWA-HRT-11-060 Date: November 2011 |
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Eleven systems combining epoxy-coated reinforcement (ECR) with another corrosion-protection system were evaluated using rapid macrocell, southern exposure, cracked beam, linear polarization resistance, and field tests. The systems included bars that were 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, three epoxy-coated bars with improved adhesion combined with the corrosion inhibitor calcium nitrite, and multiple-coated (MC) bars with an initial 50-µm (2-mil) coating of 98 percent zinc and 2 percent aluminum followed by a conventional epoxy coating. The systems were compared with conventional uncoated reinforcement and conventional ECR.
The results presented in this report indicate that the coated bars provided superior corrosion protection to the reinforcing steel. In addition, bars with damaged coatings initiated corrosion at several times the chloride contents within concrete and typically corroded at rates two orders of magnitude less than conventional reinforcement. Limited additional protection was achieved using bars with primer coating, MC bars, and concrete containing calcium nitrite and one of the organic corrosion inhibitors, although the latter resulted in reduced compressive strength and reduced resistance to surface scaling.
Jorge E. Pagáán-Ortiz
Director, Office of Infrastructure
Research and Development
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1. Report No. FHWA-HRT-11-060 |
2. Government Accession No. |
3.
Recipient's Catalog No. |
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4. Title and Subtitle Multiple Corrosion-Protection Systems for Reinforced Concrete Bridge Components |
5. Report Date November 2011 |
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6. Performing Organization Code |
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7. Author(s) David Darwin, JoAnn Browning, Matthew O'Reilly, Carl E. Locke Jr., and Y. Paul Virmani |
8. Performing Organization Report No. SM Report No. 101 |
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9. Performing Organization Name and Address University of Kansas Center for Research, Inc. 2385 Irving Hill Road Lawrence, KS 66045-7563 |
10. Work Unit No. |
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11. Contract or Grant No. DTFH61-03-C-00131 |
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12. Sponsoring Agency Name and Address Office of Infrastructure Research and Development Federal Highway Administration 6300 Georgetown Pike McLean, VA 22101-2296 |
13. Type of Report and Period Covered Final Report September 2003-February 2011 |
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14. Sponsoring Agency Code |
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15. Supplementary Notes The Contracting Officer's Technical Representative (COTR) was Y.P. Virmani, HRDI-60. |
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16. Abstract Eleven systems containing epoxy-coated reinforcement
(ECR) in combination with another corrosion-protection system are evaluated
using the rapid macrocell, southern exposure, cracked beam, linear
polarization resistance, and field tests. The systems include bars 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 (Rheocrete® 222+ and Hycrete™), an
epoxy-coated bar with a primer containing microencapsulated calcium nitrite, three
epoxy-coated bars with improved adhesion combined with the corrosion inhibitor
calcium nitrite, and multiple-coated (MC) bars with an initial 50-m (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 ECR. The coatings on all bars are penetrated
to simulate the effects of damage during fabrication and placement in the
field. The results presented in this report indicate that the coated bars provide superior corrosion protection to the reinforcing steel and that bars with damaged coatings initiate corrosion at chloride contents within concrete that are several times greater and corrode at rates that are typically two orders of magnitude below those exhibited by conventional reinforcement. Limited additional protection is achieved using bars with the primer coating, MC bars, and concrete containing the corrosion inhibitors calcium nitrite and one of the organic corrosion inhibitors, although the latter resulted in reduced compressive strength and reduced resistance to surface scaling. The differences in costs over a 75-year design life are relatively small for coated bars. Cracks in concrete directly over and parallel to the reinforcement, such as found in bridge decks, result in earlier corrosion initiation and higher corrosion rates than obtained with intact concrete for all systems. Epoxies that provide initially high adhesion to the underlying steel provide no advantage over conventional epoxy coatings. All coated bars that were evaluated exhibited corrosion losses at openings through the coating. A reduction in adhesion between an epoxy coating and the reinforcing steel occurs after a period of exposure to corrosive conditions. This reduction increases with increasing chloride content in the concrete and in the presence of cracks and decreases with the use of corrosion inhibitors, with the use of MC reinforcement, and with electrical isolation of the epoxy-coated bars from each other. Corrosion products form under the coating where adhesion has been reduced. For periods up to five years under exposure conditions representative of those in bridge decks, the reduction in adhesion between an epoxy coating and the reinforcing steel did not affect the rate at which coated bars corrode. |
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17. Key Words Adhesion, Chlorides, Concrete, Corrosion, Corrosion inhibitor, Durability, Epoxy-coated steel, Zinc-coated steel |
18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161. |
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19. Security Classif. (of this report) |
20. Security Classif. (of this page) |
21. No of Pages 255 |
22. Price |
Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized
SI* (Modern Metric) Conversion Factors
APPENDIX A. DISBONDMENT OF CONVENTIONAL EPOXY-COATED AND MC BARS IN RAPID MACROCELL TEST