When you need to protect steel from corrosion for a cable-stayed bridge spanning over 3 miles, there is a lot of steel to coat.
The Governor Mario M. Cuomo Bridge, the longest bridge in New York State, was completed in 2018 and replaced the original Tappan Zee Bridge. Crossing the Hudson River, the bridge has two spans, creating the need to coat more than 6 miles of steel. Therefore, coating application efficiencies were an absolute necessity to keep the project on track.
Off-site applications and coatings selection enable efficiencies
Due to the amount of steel used on the bridge and logistical challenges of on-site coating operations, the majority of coating work was performed off-site in shop conditions to ensure efficient, accurate applications that kept the project on schedule. Applicators coated the steel assets using a three-coat, high-performance coating system from Sherwin-Williams Protective & Marine. The system included an organic zinc-rich epoxy primer Zinc Clad III HS, an intermediate coat of Macropoxy 646, and an acrylic polyurethane topcoat of Acrolon 218 HS. This organic zinc/epoxy/polyurethane system was chosen primarily based on New York State Department of Transportation specifications and the system’s ability to deliver an expected life of 25 years or more. The applicator preferred this system due to the efficiencies it enabled related to the ease of application, as well as the fast drying and recoating times.
Applicators first prepared the steel girders to the SSPC-SP10/NACE NO. 2 Near-White Metal Blast Cleaning standard. Next, a third-party inspection team immediately verified the surface preparation so coating work could commence. Applicators applied a stripe coat first, then a full coat of the Zinc Clad III HS primer, chosen for the improved dry and recoat time, on the entire steel surface at 3 to 5 mils dry film thickness (DFT).
For the intermediate coat, Macropoxy 646 enabled wet-on-wet applications following stripe coating to enhance efficiencies, as well as the ability to apply higher DFTs in a single coat since certain areas required 6 to 10 mils DFT for added durability. Dry times were four to eight hours depending on thickness, enabling intermediate coat inspections and topcoating to progress rapidly.
The Acrolon 218 HS topcoat was applied at 3-5 mils DFT. Formulated for in-shop applications, the fast-drying acrylic polyurethane dries to touch in about one hour and can be handled in about nine hours, helping applicators promptly finish each steel girder. The topcoat provides excellent color and gloss retention for exterior exposures in an array of climates and will help the bridge continue looking great for 25 years or more.
On-site bridge assembly and coating plan enhances safety
Design-builder Tappan Zee Constructors used modular construction to assemble sections of the bridge’s structure on land before moving them into place using an enormous crane. On-site coatings applications were required during this stage for touch-ups so the edge retentive nature of the Macropoxy 646 and Acrolon 218 HS coatings were critical here to ensure sufficient DFT builds.
Teamwork and coatings selection enable efficient outcomes
On a project of the scale of the Governor Mario M. Cuomo Bridge, cooperation and efficiencies were critical so the ease of application and fast drying times for the chosen coating system enabled applicators to stay on schedule mile after mile and provide the asset owner a bridge coating system that will look and perform well for years to come.
Editor's Note: Scranton Gillette Communications and the SGC Infrastructure Group are not liable for the accuracy, efficacy and validity of the claims made in this piece. The views expressed in this content do not reflect the position of the Roads & Bridges' Editorial Team.