Materials Performance

OCT 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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OCTOBER 2018 MATERIALSPERFORMANCE: VOL. 57, NO. 10 17 Coatings NACE member Johnnie Miller, Coatings & Traffic Materials Branch Manager with the Materials and Tests Division of the Texas DOT (TXDOT) (Austin, Texas, USA) and a NACE-certified Level 3 Coating Inspector, comments that the integrity of the coating system will also affect the structural integrity of the bridge. TXDOT does use deicing salts on some of its roadways, but not as much as other states. It's the humid, subtropical marine environment of the state's coastline that contributes to many of its corrosion issues. Texas bridges are inspected every two years, and if an issue is found, the structure is put in a program to receive maintenance, rehabilitation, or replacement so any structurally deficient bridge is brought up to the national FHWA bridge inspection standards. As part of that effort, Miller's group is involved with recoating projects for many of the state's bridges. If a bridge is in an aggressive, corrosive environment, the TXDOT uses a three-coat pro- tective coating system comprised of an organic zinc epoxy primer, an epoxy intermediate coat, and a polyurethane topcoat, which is standard for the industry, he says. The state's default maintenance coating is a two-coat sys- tem that utilizes an epoxy zinc primer and an acrylic latex topcoat. New steel, however, is now being coated with an inorganic zinc primer and an acrylic latex, which allows the inorganic zinc to breathe and form a patina. Miller notes the TXDOT has used thermal spray metalizing with 99 percent pure aluminum in the field to coat steel girder bridges. Initial results, he says, show that the 99 percent pure aluminum tends to work better for corrosion control. "Zinc by its nature is a sacrificial metal, so over time it's going to get used up. We feel that the aluminum, if done right, should develop a patina and create a shell that will freeze the corrosion on the steel." Miller says that ther- mal spray metalizing has been used by TXDOT only in the last five years on a couple of structures in the field, so the department doesn't yet have a long Halls River Bridge in Florida is being built with fiber reinforced polymer (FRP) reinforcement. Cast in place and pre-stressed substructure and superstructure components are fabricated using CFRP and/or GFRP reinforcement. This Texas bridge is protected with a thermal spray 99% pure aluminum coating. Photo courtesy of Johnnie Miller, TXDOT.

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