Due to years of weathering, proximity to a waterway, and heavy traffic, a bascule bridge carrying busy U.S. 50 Business over the Wicomico River in Salisbury, Maryland was in need of a face-lift.
The Maryland DOT bridge is a Chicago type double-leaf bascule bridge built in 1962. The bridge is 127 ft long with the main lift span measuring 49 ft and the lower superstructure beam just 3.3 ft above the water level. There are roughly 1,800 linear ft of steel upper and floor beams and stringers that require protective coatings, totaling about 30,000 sq ft of steel surface area. According to the National Bridge Elements data set, 2019 edition, the steel superstructure received a Fair rating over the last 4 inspection cycles from 2012 to 2018.
Because it is one of the primary arteries for vacationers traveling toward Ocean City, prep and application occurred after the peak tourist season, and the work occurred in the cooler weather from mid-October through mid-November 2018. Additionally, work needed to be performed from barges during the daytime to limit the disruption to local traffic. In the end, the agreed-upon plan of work required a tight schedule of only 35-40 days for the contractor to complete the surface preparation and coatings application.
The preconstruction protective coating specification work was performed by GPI/Greenman-Pedersen Inc. As Charles Brown, Deputy Director of Coatings at GPI/Greenman-Pedersen Inc. shared, “We had to take into consideration the possible temperatures at that time of year as well as the constrained work schedule when selecting the protective coating system.” A traditional three-coat system may have created challenges due to the work needing to cure quickly before bridge use or near daily waterway access, coordinated with the U.S. Coast Guard and harbormaster, to ensure commercial boat traffic was not inhibited. Additionally, the coating portion was performed from late October into early November, which meant cooler temperatures. These challenges, along with the tight schedule, favored a solution that could both cure faster as well as possibly shorten the overall process by eliminating a coat. For this reason, a two-coat system was selected, consisting of Sherwin Williams Zinc Clad III HS, a three-component, polyamide epoxy, zinc rich primer with Sherwin Williams Envirolastic 940LV, a two-component aliphatic polyaspartic pigmented topcoat.
The polyaspartic coating offers a few advantages for this project, namely:
- Cures fast with a quick return-to-service compared to traditional coatings
- Applies at higher dry film thickness which allows the reduction in number of coats
- Cures at cooler temperatures in the shoulder seasons
- Offers color/gloss retention equivalent to that of polyurethane systems
The painting contractor, Blastech Enterprises, utilized two barges to perform the majority of the work. They started by abrasive blasting to a SSPC-SP 10/NACE No. 2 finish. The primer was sprayed at 3.0-5.0 mils DFT then stripe coated on joints and welds. The polyaspartic topcoat was stripe coated first, then applied at 6.0-9.0 mils DFT.
The coating application process took four days and was finished well ahead of the completion target date, in part due to the polyaspartic coating’s positive traits of fast cure and high build.
