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Maintenance is an essential element in prolonging any structure’s lifecycle, particularly steel structures. Maintaining a bridge’s paint coatings system throughout its lifecycle is crucial to protecting its reliable infrastructure functionality and longevity, enabling the bridge to last decades longer than it would without maintenance painting.

A bridge's coating system is the first line of defense against corrosion. People often mistakenly believe that the coating is for aesthetics, and while that is important, its primary job is protecting structural steel and concrete. A solid coating foundation and coating system maintenance allows bridges to last throughout their designed service life without weakened capacity or the need for major rehabilitation, preventing it from potentially turning into a public safety issue or a major preservation project, public cost and service interruption.
Approximately 30 percent of the 607,000 bridges in the Federal Highway Administration’s (FHWA) National Bridge Inventory have steel superstructures. With many bridges approaching or exceeding their 50-year design life, there is an increasing number of bridges in need of repairs, replacement or repainting. In the past, major bridge owners had in-house bridge maintenance painting forces. More recently, inadequate funding and higher costs of labor and materials have eliminated this routine coating system maintenance, causing repainting efforts to be deferred, exacerbating the structural condition issues.


The current most common bridge coating system is a three-coat system, including a zinc-rich primer, an epoxy intermediate coat and an acrylic polyurethane topcoat. This is typically used when painting a new bridge or stripping off another system, starting over from scratch. While it might be the most common system, it is not the only option.

Choosing the right coating for a bridge is very different from deciding on paint colors for a building. Analyzing the weather, location, application costs and challenges, geography and owner preference are all a part of the decision-making process. Different parts of the country require different treatments to accommodate temperature, wind, humidity and precipitation. While a moisture-cured system works for a foggy, rainy environment like Seattle, that is not essential in Oklahoma, where salt and moisture are less prevalent. 

Location and local interests play a large role in the color of a bridge. Gray bridges are preferred and populate Louisiana’s flat wetlands and major river crossings, whereas Pittsburgh’s bridges are famous for their “Aztec gold.” Geographic features can also affect what color a bridge is painted, with blues used over water, green and brown used over mountains and black historically used on railroad bridges either to emphasize strength and utilitarianism or just as the consequence of desired coating chemistry. These color choices can sometimes help bridges fade more seamlessly into the scenic background like a chameleon. Certain colors are more likely than others to fade over time. Without adequate color retention and ultraviolet (UV) protection from the sun, bridges may need to be touched up more often for aesthetic purposes. When bridges are repainted, it may not need to be done all at once, so staying consistent with colors and taking previous paints into consideration allows the re-coating process to be done in phases, as budget permits.

During the first inspection, a coatings assessment is conducted. The current paint is analyzed, and a recommendation is provided to the owner of the bridge for what services are required, whether it be spot removal, zone painting, full overcoating or total removal and replacement of the existing system. Once the plans and specifications for repainting are drawn up, platform and containment installation begin, with temporary work platforms and sky climbers provided for the painters. Once the colors and system manufacturer are submitted, the physical process of repainting the bridge can begin.
Since many of the structures being repainted today were originally constructed with lead-based paint or other potentially hazardous component materials, there are a number of precautions that teams must take. Workers must participate in training on lead hazards, respirator fit tests and blood tests for their own protection. On-site showers allow workers to wash off after blasting and removing lead-based paint. The establishment of specific environmental and worker health and safety regulations by the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) must be followed closely to limit generation and handling and provide proper disposal or preferred recycling of waste containing toxic materials.
After blast cleaning to remove prior coatings and establishing proper surface preparation, the new coats are applied and inspected for dry film thickness measurement and complete coverage of the steel or the prior coat. Daily reports, quality assurance inspections, photographs, monthly estimates and progress meetings all work to keep the project on track and well-documented for future reference. During the final inspection, a punch list is created to document any items that still need to be completed.


Once the final inspection is complete, the task of maintenance begins. Adequate inspections should be performed every one to two years, so minor touch-ups can be addressed quickly, fixing everything from rust spots to bubbling paint before they become major blemishes. Certain amounts of corrosion warrant smaller maintenance projects in order to preserve the life of the bridge, spot or zone cleaning, and applying new paint coatings in those areas. After 13 to 20 years, depending on how often regular maintenance occurs and the wear and tear on the bridge, maintenance painting is conducted; at year 28, a full overcoat; and around year 40, the entire system should be removed and replaced. Since dirt, debris and residual salts from de-icing efforts, if employed, can sit on horizontal flat surfaces and eat away at the paint, pressure washing once a year is also a great way to help the system stay intact and is the least costly preservation method to protect the structure’s coating system.

Avoiding the need for bridge closures to accomplish required major structural issues should be a paramount concern. Painting is often an afterthought, as owners may prefer to allocate funds toward new bridges or a larger rehab project. Oftentimes, there may not be enough money budgeted for a maintenance program at all, but updating paint coatings is a necessary component of maintenance that helps extend the life of a bridge, resulting in long-term savings. If maintained correctly throughout its lifecycle, a bridge coating system can last up to 50 years or so, depending on its environment. While a bridge coating system can’t prevent all corrosion, it can slow the rate at which it happens. Without this system, structural integrity problems are bound to accelerate.
Paint colors and protective coatings are for far more than beautification. The best system protects against weather, chemicals, corrosion, fire and other forces that can damage a structure. It’s important to take a long-term approach to any bridge’s coating system and maintenance. A bridge’s true beauty and functionality lies beneath the color of the topcoat.


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