Corrosion Protection of Steel Bridges Using Duplex Coating Systems (2023)

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2023 N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP RESEARCH REPORT 1048 Corrosion Protection of Steel Bridges Using Duplex Coating Systems J. Peter Ault Elzly Technology Corporation Vineland, NJ Subscriber Categories Bridges and Other Structures • Maintenance and Preservation • Materials Research sponsored by the American Association of State Highway and Transportation Ofcials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transporta- tion results in increasingly complex problems of wide interest to high- way authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation, under Agree- ment No. 693JJ31950003. The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRB’s recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive com- mittee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, univer- sities, and industry; TRB’s relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists in highway transportation matters to bring the findings of research directly to those in a position to use them. The program is developed on the basis of research needs iden- tified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the FHWA. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&I’s recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement, rather than to substitute for or duplicate, other highway research programs. Published research reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet by going to https://www.mytrb.org/MyTRB/Store/default.aspx Printed in the United States of America NCHRP RESEARCH REPORT 1048 Project 12-117 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-69878-8 Library of Congress Control Number 2023939224 © 2023 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trade- marks of the National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, APTA, FAA, FHWA, FTA, GHSA, or NHTSA endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. NOTICE The research report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the National Academies of Sciences, Engineering, and Medicine. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The Transportation Research Board does not develop, issue, or publish standards or spec- ifications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names or logos appear herein solely because they are considered essential to the object of the report.

e National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. e National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president. e National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. e three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. e National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org. e Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. e mission of the Transportation Research Board is to provide leadership in transportation improvements and innovation through trusted, timely, impartial, and evidence-based information exchange, research, and advice regarding all modes of transportation. e Board’s varied activities annually engage about 8,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. e program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

C O O P E R A T I V E R E S E A R C H P R O G R A M S CRP STAFF FOR NCHRP RESEARCH REPORT 1048 Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program Ahmad Abu-Hawash, Senior Program Officer Sheila A. Moore, Program Associate Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications NCHRP PROJECT 12-117 PANEL Field of Design—Area of Bridges Ivan R. Lasa, Lasa and Associates Corrosion Services, Gainesville, FL (Chair) Joshua Charnosky, Pennsylvania Department of Transportation, Harrisburg, PA David M. Dobson, Oregon Department of Transportation, Salem, OR Michael Hewins, Massachusetts Department of Transportation, Boston, MA Qindan Huang, Marquette University, Milwaukee, WI Steven Kahl, Michigan Department of Transportation, Lansing, MI Johnnie S. Miller, Round Rock, TX Jerry S. Zoller, New Hampshire Department of Transportation, Concord, NH Ping Lu, FHWA Liaison

NCHRP Research Report 1048: Corrosion Protection of Steel Bridges Using Duplex Coating Systems, presents recommendations for the use of duplex coatings for corrosion protection of new and existing steel bridges. These recommendations are based on case studies, laboratory testing, and users’ input. The recommendations provide bridge owners and practitioners with a resource to help increase the service life of coated steel bridges. Bridge coatings greatly contribute to the longevity of steel bridges and reduce the total life-cycle cost by protecting steel bridge members from corrosion. For most steel bridges across the nation, the most popular practice is to provide a three-coat, zinc-rich primer system. The three-coat system generally requires regular maintenance (touch-up); other- wise, the bridge may have to be completely overcoated or the coating be removed and replaced prematurely. This approach has proven to be a maintenance challenge for bridge owners. While efforts are ongoing to improve the service life of traditional coating systems, another approach would be the use of “duplex systems” (hot-dip galvanized or metallized with a coating system) to provide long-term protection against corrosion. Research indicates that the synergetic life of duplex coatings will extend the bridge service life beyond the tradi- tional coating systems. Unfortunately, bridge owners have had mixed experiences with duplex coatings. Some DOTs have had great success with the duplex coating systems, while others have had issues with galvanizing and metallizing quality, have experienced adhesion problems with the finish coating, or have had to perform maintenance painting of the duplex coating systems sooner than anticipated. The processes are currently reliant on the experience of the galvanizers, metallizers, and coating applicators with a lack of guidelines. As a result, and to be consistent, there was an immediate need to develop guidelines for bridge owners on the use of duplex coating systems for corrosion protection of steel bridges. Under NCHRP Project 12-117, “Guidelines for Corrosion Protection of Steel Bridges Using Duplex Coating Systems,” Elzly Technology Corporation was asked to develop recom- mendations for corrosion protection using duplex coating systems for extending the service life of steel bridges and to conduct a workshop to demonstrate the use of the recommenda- tions to an audience of DOT staff and other stakeholders. The recommendations cover the selection and application of duplex coating systems during the design of new steel bridges and the maintenance and rehabilitation of existing steel bridges. In addition to the research agency’s report, two deliverables—appendices and workshop training materials—can be found on the National Academies Press website (nap.nationalacademies.org) by searching on NCHRP Research Report 1048. F O R E W O R D By Ahmad Abu-Hawash Staff Officer Transportation Research Board

1 Summary 3 Literature Review 3 Background 4 Defining a Duplex System 4 Critical Issues for Duplex Coating Systems 10 Electrochemical Mechanism of Organic Coating Delamination 14 Performance of Duplex Coatings 17 State Specifications 19 Laboratory Testing 19 Summary 21 Metallic-Coated Sample Preparation 21 Study 1—Quantitative Detection of Zinc Hydroxide (HDG) and Oxides (TSC) 34 Study 2—Comparison of Epoxy Coatings from Three Manufacturers to Select a Product for Further Testing Under Study 3 39 Study 3—Adhesion of Epoxy Coating over Various Concentrations of Oxides (HDG and TSC) After Cleaning Using Different Methods of Preparation 66 Study 4—Slip Resistance Testing (Faying Surfaces of Slip-Critical Connections) 69 Study 5—Segmented-Cell Testing of Metallic Duplex Systems 87 Field Case Studies 118 References 120 Appendices A through L C O N T E N T S