Moisture-Cure Coatings Tackle Corrosion, Humidity and Cold Weather at Wisconsin's Renovated Cass Street Bridge
DALLAS, February 13, 2007 - The 66-year-old Cass Street Bridge is an exceptionally busy thruway for commuters and a critical artery between LaCrosse, Wis., and La Crescent, Minn. The open-grid deck bridge features 18 spans over the Mississippi River with 17 piers that support more than 2,500 feet of steel.
After years of harsh Wisconsin winters, the heavily traveled bridge was showing its age and in need of extensive renovation. Dan Kleinertz, project manager, Wisconsin Department of Transportation, noted that there were several problems with the deck. "While rain was able to drain through, cold weather brought hard packed snow and ice that sunk into grid spaces and sat on the underlying structures." This, combined with roadway deicing chemicals, resulted in significant corrosion to these areas.
To help solve the problem, the grid deck was replaced with a new concrete roadway and the underlying support system was also fortified to support the new load.
The next step in the renovation process was painting. Rainbow Inc., the painting contractor, prepared the metal surfaces to meet SSPC standard SP-10, "Near White" Blast. Since bridges in the state are repainted every 20 to 25 years, a coating was needed that would offer long-lasting protection. Given Wisconsin's inclement fall, winter and spring weather, and the project's timetable (May 2005 to June 2006), a coating system that could also withstand wet weather during application and extend the application window was important to keeping the project on time and on budget.
Chosen was a three-part moisture curing urethane coating system from Sherwin-Williams. The system includes Corothane® I Galvapac Zinc Primer, Corothane I Ironox® B intermediate coat and Corothane I Ironox A topcoat. All three coatings contain polyurethane resins manufactured by Bayer MaterialScience. With these coatings, ambient humidity aids the curing process rather than threatens it. The three coatings in the system are VOC compliant. They were designed for low temperature application with conventional spray equipment at temperatures as low as 20 degrees F.
"These coatings are great for extending the painting season, especially in colder climates," says Mike Debuhr, industrial division manager, Rainbow, Inc.
One of the more versatile types of coatings for use on steel substrates, moisture-curing urethanes are surface tolerant, quick drying, and applicator-friendly. They offer excellent impact resistance, and wear and abrasion resistance, providing long-term durability. In abrasion resistance tests, moisture-curing polyurethanes average only about 10 to 30 milligrams film loss.
Moisture-cured polyurethanes penetrate into pores and tight crevices, where moisture is usually present, to form strong chemical bonds - reducing the risk of blisters caused by water trapped under the coating film.
Department officials were pleased that the project was completed on time - June 30, 2006 - and the bridge will provide yet another generation with convenient access to downtown La Crosse.
For more information about Corothane I Galvapac Zinc Primer, Corothane I Ironox B intermediate Coat, and Corothane I Ironox A Topcoat from Sherwin-Williams, call 1-800-524-5979 or visit www2.sherwin-williams.com.
For more information on Wisconsin Department of Transportation call, 608-792-1367.
For more information on polyurethane resins from Bayer MaterialScience, call 800-662-2927 or visit www.BayerMaterialScienceNAFTA.com
Bayer MaterialScience LLC is one of the leading producers of polymers and high-performance plastics in North America and is part of the global Bayer MaterialScience business with nearly 19,000 employees at 40 sites around the world and 2005 sales of 10.7 billion euros. Our innovative developments in coating, adhesive and sealant raw materials, polycarbonates, polyurethanes and thermoplastic urethane elastomers enhance the design and functionality of products in a wide variety of markets, including the automotive, construction, electrical and electronics, household and medical industries, and the sports and leisure fields. Our inorganic basic chemicals unit produces chlorine and related essential products for the chemicals industry. Let us give life to your vision. Bayer MaterialScience - Where VisionWorks.
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The Cass Street Bridge features 18 spans over the Mississippi River, connecting La Crosse, Wis. and La Crescent, Minn.
First the old bridge grid deck was removed and painting contractor Rainbow, Inc. blasted the tops of the underlying support. They then primed the areas that would be covered either by the new concrete deck or the additional support system with Corothane® I Galvapac Zinc Primer.
Since bridges are repainted only every 20-25 years, the coating must offer long-lasting protection. A three-part moisture curing urethane coating system from Sherwin-Williams was selected for this application. It included Corothane® I Galvapac Zinc Primer, Corothane I Ironox® B intermediate coat and Corothane I Ironox A topcoat.
