![]() These two-coat systems eliminate the intermediate epoxy layer, so painting a steel overpass can be completed overnight. In humid environments, for example, maintenance personnel use three coats of zinc-rich moisture-cured urethane (MCU)/MCU/polyurethane paint system.Ī new class of coating systems consisting of a zinc-rich primer topcoated with fast-dry, high-build (thick film) polyaspartics, polyurethane, or polysiloxane promises anti-corrosive results that are comparable in some situations with the three-coat systems. Many States use the three-coat paint system as the preferred method of protection. Nearly 20 years ago, research led to the current standard, which is a three-coat system of zinc-rich primer/epoxy/polyurethane paint. Further, the presence of potentially hazardous substances in the existing paint complicates maintenance processes and dramatically increases related costs. Often, harsh environments and exposure to roadway deicing chemicals (salts) intensify the effects of the natural aging process. Subsequent painting for preventive maintenance and corrosion protection was rare and generally reserved for larger spans.īecause the majority of the steel bridges in the interstate system were built between 19, many have little protection from corrosion because their coating systems have outlasted their useful lives. Over the course of several days, bridge workers would apply the paint directly onto the mill scale (black corrosion analogous to rust) that adheres to the formed steel when it is heated. Until the late 1970s, virtually all steel bridges in the United States were protected from corrosion by paint systems that consisted of three to five thin coats of alkyd paint containing toxic lead and chromate. FHWA is studying the effects on costs of using two-coat painting systems on steel bridges and overpasses. This New York City worker is applying a coating to a steel bridge structure. This research studies two-step painting systems as a possible alternative for protecting steel bridges and overpasses from corrosion.
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