Above: During installation, aggregate is immediately shoveled across the surface once the epoxy has been applied. Facing page: The initial coat of epoxy is applied at approximately 1/16 inch or about 3 gallons per 100 square feet. Aggregate is shoveled onto the epoxy. Then, a second coat is applied following the same protocol, but at a thicker rate. The final profile is about 3/8-inch thick. Photos: Kirk Duffy, Cargill Inc.
Two years ago, Gary Williams, a district bridge engineer for the Pennsylvania DOT (PennDOT), attended a presentation about a new aggregate epoxy overlay technology during a bridge conference. The overlay, it was said, improves traffic safety while simultaneously protecting infrastructure. It sounded intriguing enough that he hung on to the information.
Not much later, Williams found himself confronted with the dual problem of pavement preservation and potential winter icing conditions on the Johnson Creek Bridges on Route 15 just south of Blossburg, Pa. The curved, concrete bridges span a scenic stream where summertime fly-fisherman cast for trout. But in winter, when bridges freeze before roads, icing is a problem.
In the past PennDOT had used latex-modified concrete overlays to restore ride smoothness and mitigate chloride penetration. But while these overlays minimized water seepage and intrusion of corrosive agents, they didn't prevent icing.
As PennDOT mulled options, Williams recalled the technology he'd heard about and realized that it could provide a single solution to both issues. “It seemed to me this might help the traffic folks address safety needs and at the same time get an overlay on these bridges to help with maintenance,” he says.
The overlay, a patented combination of epoxy and aggregate rock, provides a complete pavement seal to protect infrastructure and provide year-round traction in all weather conditions.
It also stretches anti-icing budgets. The overlay acts like a rigid sponge, storing anti-icing chemicals and automatically releasing them to help prevent frost or ice from forming on road or bridge surfaces. Thus, a single application of standard anti-icing chemicals can treat multiple frost and ice events.
The possibility of safety plus infrastructure protection was too ideal for Penn-DOT to pass up. The department applied for—and received—a grant from the Federal Highway Administration's Innovative Bridge Research and Construction (IBRC) program, designed to help government agencies incorporate innovative materials and technologies into bridge projects.
Even with a $150,000 IBRC grant in hand to offset the $694,000 project, Williams says, there was “some skepticism” about using the new overlay. PennDOT decided to test it before moving ahead with the Route 15 bridge surface project, which at 65,000 square feet would represent the largest installation anywhere of the product.From Small To Large
Using its own financial resources, PennDOT installed SafeLane Surface Overlay's aggregate epoxy surface overlay on a 3400-square-foot bridge along State Route 660 near Mansfield. SafeLane overlay is licensed and marketed by Minneapolis-based Cargill Inc. As the elements tested the overlay, results were positive.
Maintenance workers reported that when other roadways were snow-packed, the overlay test site remained slushy with no compacted snow. In addition, no weather-related crashes were reported on the bridge.