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|Federal Highway Administration > Publications > Public Roads > Vol. 61· No. 1 > Steel Bridge Coatings Research|
Steel Bridge Coatings Research
by Robert A. Kogler Jr. and Shuang-Ling Chong
The development of the Interstate Highway System (and subsequently, the National Highway System) over the past 40 years has marked a milestone in the history of private and commercial transportation. This infrastructure represents a vital component in the growth and sustenance of the U.S. economy and the American culture.
A primary goal in the development of the interstate system was to provide rapid and contiguous vehicular access to all parts of the nation from any other point in the country. Over the past several years, this goal has essentially been achieved, and through the use of the Highway Trust Fund, it was achieved without incurring long-term national debt.
Use of laboratory cyclic accelerated test cabinets is one of the several ways that coating materials are tested.
Until the mid to late 1970s, virtually all steel bridges were protected from corrosion by three to five thin coats of alkyd paints containing toxic lead and chromate. Paint is applied directly over the mill scale (a black scale of magnetic oxide of iron formed on iron and steel when heated for processing) that is adherent to the formed steel. Subsequent painting to ensure the continued prevention of corrosion has been rare, and painting for preventive maintenance has generally only occurred on larger bridge structures and toll bridges. Because the majority of the steel bridges in the interstate system were constructed between 1950 and 1980, most of these structures were originally painted in this manner. This means that a very large percentage of the steel bridges in the interstate system are protected from corrosion by a coating that is beyond its useful life and that contains pigments hazardous to humans and the environment.
Maintaining corrosion protection of steel bridges presents a major challenge to bridge owners. Not only are a large percentage of existing steel bridges reaching a critical level of deterioration, but the cost and logistical problems associated with necessary steel and coating system maintenance are compounded by the lead-containing paints used to coat most of these bridges.
Traditionally, the Federal Highway Administration's (FHWA's) role in bridge painting has been limited to new construction and major roadway rehabilitation projects - projects funded in whole or in part with federal monies. Recent changes in federal allocations (e.g., the Intermodal Surface Transportation Efficiency Act of 1991) have shifted federal dollars to routine maintenance projects, requiring a change in the scope of the mission of the FHWA technical community. Because FHWA is now required to provide responsible technical input throughout the maintenance life cycle of the nation's bridges, the focus of research and field support efforts must be changed to maximize the life-cycle cost-effectiveness of the materials and technologies recommended by FHWA for bridge preservation.
For the past several years, FHWA's Turner-Fairbank Highway Research Center (TFHRC) has administered research programs aimed at defining the most cost-effective means of protecting steel bridge structures with durable coatings. Particular focus was given to this issue in 1987 with the establishment of a High- Priority National Program Area (HPNPA) for bridge coatings. This program has targeted the key issues of coating material performance, surface preparation requirements, corrosivity of various environments, environmental compliance and impact, toxicity characteristics, and containment and disposal of waste generated during typical bridge repainting projects. Several of these research efforts are complete with some key findings well into implementation and others are coming to fruition in the next year.
This article outlines the various projects conducted under the bridge coatings HPNPA and provides the key overall findings.
The objective of the HPNPA is to conduct necessary research to assist highway bridge owners to optimize steel bridge corrosion-control operations. Specifically, efforts focus on the following:
Description of Projects
The bridge coatings HPNPA consists of the following research projects:
Key Technical Issues
Program results are focused on several key technical issues that are expected to become increasingly important in the bridge coating area.
Life-Cycle Cost Minimization
As maintenance budgets continue to shrink or, at best, remain static and as the cost of bridge maintenance continues to rise, the focus for expenditures must shift to achieving long-term effectiveness for the dollars spent. This is a radical change in philosophy for a majority in the bridge painting industry. To date, bridge maintenance painting has been based on incremental budgets rather than life-cycle considerations. Now, bridge owners must have a fundamental understanding of the life-cycle cost impacts of bridge painting operations so they can maximize the return on the large investment necessary to maintain the country's bridges.
Several of FHWA's research projects under the bridge coatings HPNPA have addressed the life-cycle cost issue in detail. Among these are the Lead-Containing Paint: Removal, Containment, and Disposal project and the Environmentally Acceptable Materials for the Corrosion Protection of Steel Bridges project. The research on the removal of lead-containing paint considered the relative cost increases associated with changing regulations that deal with removal and handling of hazardous debris during bridge maintenance painting operations. The other project, which investigated environmentally compliant materials and tested low volatile-organic-compound (VOC) coating systems, focused on the relative cost/benefit of the durability of various paint systems based on performance data and relative costs of material and application
In addition, another project, Issues Impacting Bridge Painting, performed an extensive life-cycle versus initial-cost analysis for various bridge painting scenarios. The results of this study are in the form of a spreadsheet program, which is useful in comparing the various maintenance painting options based on a life-cycle cost analysis.
The common findings of these programs with respect to cost considerations are: (1) the relative cost of paint material is almost always insignificant when viewed in terms of the overall cost of the bridge maintenance job, and (2) the advantage in the relative durability of the better coating systems often far outweighs the nominally increased cost of these materials at the time of application. In general, for moderately to severely corrosive environments, the most durable options in the coating material and in the surface preparation system will be the optimum choices from a life-cycle cost standpoint.
Successful minimization of life-cycle costs for bridge maintenance requires: (1) accurate data concerning cost and material performance and (2) user-friendly tools for assessing the relative cost impacts of various maintenance options. Models that present the relative cost of available maintenance strategies must be developed. These models must be constructed using sound engineering, planning, and economic principles, and the intended audience (i.e., bridge engineers) must be able to easily understand and use the model in real-world decision-making processes.
The effectiveness and safety of paint removal operations have been investigated using a containment mock-up.
Over the past few years, environmental regulations have become the single most influential force affecting the bridge painting industry. Specifically, the regulations regarding the VOC content of protective coatings and the environmental and worker health and safety regulations associated with the removal of lead-containing paint have had a significant impact on the bridge painting industry. Table 1 (below) lists the most pertinent regulations and summarizes their effect on bridge painting operations.
These regulations impact all aspects of bridge painting from construction, to rehabilitation, to routine maintenance. A fundamental understanding of these regulations has become a prerequisite for personnel at all levels of bridge maintenance painting. In fact, the current litigious atmosphere surrounding bridge painting is a result of the industry's learning curve in this area. This situation has become serious in some cases and threatens to derail ongoing efforts to maintain and upgrade the condition of the infrastructure.
Projects sponsored by FHWA have had a significant impact on the implementation of measures to comply with regulations in a cost-effective manner. The Lead-Containing Paint: Removal, Containment, and Disposal project provided bridge owners with detailed information regarding the design and construction of containment structures for abrasive blasting operations. This program investigated the details of ventilation design and provided results that are useful in protecting the environment, the public, and workers, while maintaining a productive bridge painting operation. In addition, considerable information regarding the proper handling, treatment, and disposal of abrasive blasted wastes was developed. This information continues to have a direct impact on regulatory development and enforcement. Data from this program have been used in the development of regulatory language by the Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA) and in the development of standard practices by industry organizations, such as the Steel Structures Painting Council.
Materials testing projects - such as Performance of Alternative Materials in the Environment, Comparison of Laboratory Testing Methods for Bridge Coatings, and Environmentally Acceptable Materials for the Corrosion Protection of Steel Bridges - have also had a direct influence on regulatory development and the development of measures for compliance by bridge owners. These projects provided critical, long-term performance data for many new, environmentally compliant bridge paint materials. These data have provided justification for bridge owners to move away from technologically old, lead-containing paints to new, more durable formulations that contain little or no toxic pigments and significantly less solvent. The data produced by these projects have formed a basis for the overall advancement of the bridge painting industry into more durable, higher value-added coating materials that will comply with environmental regulations and provide superior protection for bridge steel in comparison with traditional bridge paints. Because environmental compliance is a cost element that continues to increase disproportionally to other bridge-painting cost variables, providing input to the regulation development process has been an essential and ongoing function of the HPNPA program. The EPA regulation regarding the allowable VOC content of architectural and industrial maintenance coatings was partially developed through a regulation-negotiation (reg-neg) effort. FHWA actively participated in this process and provided high-quality performance data for bridge coatings, indicating the state of technology for various types of coating systems. Data from the bridge coatings HPNPA projects also had direct influence on the development of EPA and OSHA regulations regarding the effects of lead-containing paint on workers and the environment and regarding the reconsideration of EPA efforts to regulate the zinc content of paints. Several of the programs demonstrated the performance merits of paint systems employing zinc-rich primers, particularly in salt-rich exposures.
Environmental and worker health and safety data are currently being collected during ongoing field operations.
Research is underway to address several outstanding issues. One is the establishment of the optimum methods for determining the applicability of lower cost maintenance painting for existing structures. Another subject of study is the relative importance of various environmental variables on the subsequent corrosivity of a potential bridge site. A third issue is the appropriateness of current emissions-monitoring protocols for environmental compliance during surface-preparation operations. Current research is also addressing application and performance parameters for waterborne inorganic zinc coatings.
Present research efforts in the Containment Efficiency: Environmental and Worker Protection project should have a continued direct effect on the state of the practice for protecting workers and the environment during bridge painting. This project seeks to affect the development of future regulations and to provide guidance to regulators regarding appropriate conditions of enforcement on actual job sites.
The ongoing Corrosivity of the Environment project quantifies the different environmental variables that may influence the deterioration rate of coating systems at a particular site. The aim of this program is to use this information to estimate corrosion rates of steel structures in specific locations around the country. This information will eventually be useful to bridge engineers in choosing appropriate corrosion control for structures during design.
Advanced Material Testing Protocols
With the rapid changes in materials occurring in the industrial maintenance coatings industry, the need for laboratory and field test protocols that provide high-quality data in a relatively short period of time is ever increasing. FHWA's bridge coatings research program has attempted to address this need by developing and analyzing the effectiveness of innovative coatings test procedures while evaluating the durability of new coating systems. Specifically, the projects Performance of Alternative Coatings in the Environment (PACE), Environmentally Acceptable Materials for the Corrosion Protection of Steel Bridges, Effects of Surface Contaminants on Coating Life, Maintenance Painting of Steel Bridges, Issues Impacting Bridge Painting, Methodology for Evaluation of Corrosion Control Coatings, and Comparison of Laboratory Testing Methods for Bridge Coatings have had aspects that addressed the need for higher quality and shorter term coating-durability data.
In particular, the PACE study pointed to the need for statistical significance in coating testing, and the in-house study Comparison of Laboratory Testing Methods for Bridge Coatings, which compared accelerated test methods, provided significant findings in the area of cyclic corrosion testing. This project provided a vast improvement in correlation with parallel outdoor exposure testing compared to previously used laboratory (salt fog) testing.
Still ongoing is a cooperative effort with the National Institute for Standards and Technology. This study is examining in detail the effects of particular environmental stresses on a coating system and is attempting to quantify the effect of each variable.
Over the past several years, the bridge coatings research efforts sponsored by FHWA have produced significant results for bridge owners. Future efforts will be focused on the implementation of durable, environmentally compliant coatings and improved maintenance practices. In addition, the program will stay abreast of future developments in regulations that affect the industry and will continue to develop useful data regarding new and upcoming technologies that promise more durability or lower overall cost for bridge maintenance operations. The focus will be on the development of data regarding alternative, cost-effective corrosion control and coatings technologies that provide a significant benefit to bridge owners. Also, data already developed under the HPNPA program will be formatted and delivered to bridge engineers in the most useful manner possible.
The recently formed FHWA Bridge Coatings Technology Outreach Team will spearhead these efforts. This team consists of engineers from several FHWA divisional and regional offices, as well as researchers from FHWA headquarters. The team has been successful at accelerating the delivery of key research results to field operators.
Robert A. Kogler Jr. is a research materials engineer in the Special Projects and Engineering Division of FHWA's Office of Engineering Research and Development. Before becoming a part of the FHWA's Steel Bridge Coatings Research Program, he worked in private industry for eight years. He earned his bachelor's degree in materials science and engineering from the University of California, Berkeley.
Dr. Shuang-Ling Chong is a research chemist in the Special Projects and Engineering Division of FHWA's Office of Engineering Research and Development. Her 27 years of research experience includes chemical kinetics of photolysis and ion-molecule reactions, supercritical fluid extraction of oil shale, fractionation and characterization of organic materials in fossil fuels and petroleum, identification of toxic organics and metals in coal combustion residues, evaluation of coatings for steel bridges, leaching studies of paint debris, determination of physical and chemical properties of paint, and failure analysis techniques for bridge coatings. She is currently conducting staff research in paint testing and performance studies of low volatile-organic-compound coating systems for steel bridges. She received her bachelor's degree from National Cheng Kung University in Taiwan. She earned her master's degree and doctorate in physical chemistry from Rutgers University.
Table 1 - Regulations Impacting the Bridge Painting Industry
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