May 2, 2012
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YUKON TRAINING RANGE, Alaska — A new type of vinyl coating system that can be applied in sub-freezing temperatures also complies with emission standards for volatile organic compounds (VOC). ERDC Construction Engineering Research Laboratory (CERL) demonstrated the coating on a bridge at Yukon Training Range, Alaska, and is continuing to monitor its performance.
Battling corrosion with coatings
Protective coatings are the primary method for preventing and controlling corrosion on steel structures at military bases. However, in the case of bridges, the coating systems must either be applied during warm weather or else the section of the bridge being painted must be pre-heated. For cold regions, these constraints result in a small window of the year when work can be done, creates difficulty in completing projects, and escalates the cost.
"The service life of a bridge coating depends on a number of things, including both the corrosivity of the environment as well as the amount of physical damage the surface receives, such as that from loose gravel being thrown by traffic," said Al Beitelman, CERL researcher and director of the Corps of Engineers Paint Technology Center. "Even bridges on hard-surfaced roads need to be recoated in 15 to 20 years."
Solution-type vinyl coatings have been used for decades to protect metal water structures such as locks, dams, bridges, and ships. They have high levels of durability and a long service life. As lacquer coatings, they can be applied through an extremely wide temperature range. However, they also have an often unacceptably high level of VOCs, for which the Environmental Protection Agency sets emission standards.
In bench evaluations, the new technology showed promise of allowing vinyl to meet the most restrictive VOC regulations. The material can be manufactured with a high percentage of an exempt solvent to produce a sprayable vinyl coating with a VOC of less than 100 grams per liter. Since it can be applied in temperatures below 32 degrees Fahrenheit, it extends the timeframe in which the recoating work can be done.
Coating tested at Fort Wainwright
To demonstrate and validate the new coating system, CERL worked with the Fort Wainwright, Alaska, Directorate of Public Works (DPW) to identify an appropriate steel structure to be repainted. The Department of Defense Corrosion Prevention and Control Program funded the project.
Fort Wainwright, located adjacent to Fairbanks, has temperatures varying from a high of 94 degrees (1991) to a low of minus 66 degrees (1961). The Yukon Training Range is situated south of the fort and is shared with Eielson Air Force Base. The regional Installation Management Command named Yukon Training Range as the test location and coordinated with Wainwright DPW to select a specific Bailey bridge to be recoated.
The existing lead-based paint on the bridge had to be removed before the low VOC coating system could be applied. To avoid contaminating water under the bridge or surrounding soil during removal, project managers decided to use a crane to lift the bridge off of its embankment and place it on the adjacent road, where a containment enclosure would be built in place.
Before coating, all metal on the bridge was dry-abrasive blasted to Steel Structures Painting Council SP 10, "Near White Metal Blast Cleaning." Once the coating dried, the blasting waste was collected and disposed of following regulatory requirements. The crane lifted the bridge back onto the embankment, approach ramps were replaced, and new wood planking was installed.
Validating the system's performance
During the application process, the research team also blast-cleaned 12 mild steel test coupons. They coated six of them at the same time as the bridge, while the rest were left uncoated. Then they mounted all of the coupons on a rack and positioned them at a 45-degree angle from the vertical, attaching the rack to the bridge so as to be exposed to the same sunlight and environmental conditions as the bridge. At 12 and 24-month intervals, two each of the coated and uncoated coupons will be removed and delivered to the Paint Technology Center to assess the coating’s performance, including an analysis of the cause and extent of any corrosion that appears.
"The application went very smoothly," Beitelman said. "The coating dried within minutes, which allowed substructures to be handled without damaging the freshly applied coating. The coating has a pleasing appearance with excellent adhesion, and is extremely tough. I do not expect it will need any touch-up or other maintenance for decades."