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REPORT
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Publication Number:  FHWA-HRT-11-060    Date:  November 2011
Publication Number: FHWA-HRT-11-060
Date: November 2011

 

Multiple Corrosion-Protection Systems for Reinforced Concrete Bridge Components

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FOREWORD

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

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

 

Technical Report Documentation Page

1. Report No.

FHWA-HRT-11-060

2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

Multiple Corrosion-Protection Systems for Reinforced Concrete Bridge Components

5. Report Date

November 2011

6. Performing Organization Code

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

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.

11. Contract or Grant No.

DTFH61-03-C-00131

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

14. Sponsoring Agency Code

15. Supplementary Notes

The Contracting Officer's Technical Representative (COTR) was Y.P. Virmani, HRDI-60.

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-Mum (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.

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.

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

Table of Contents

CHAPTER 1. INTRODUCTION

CHAPTER 2. EXPERIMENTAL WORK

CHAPTER 3. TEST RESULTS

CHAPTER 4. EVALUATION

CHAPTER 5. CONCLUSIONS

APPENDIX A. DISBONDMENT OF CONVENTIONAL EPOXY-COATED AND MC BARS IN RAPID MACROCELL TEST

APPENDIX B. CORROSION LOSS REQUIRED TO CRACK CONCRETE CONTAINING CONVENTIONAL, EPOXY-COATED, AND GALVANIZED REINFORCEMENT

ACKNOWLEDGMENTS

REFERENCES


List of figures

List of tables

 

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