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.
PennDOT managers felt confident enough in the overlay's winter performance to proceed with the Johnson Creek Bridges project on Route 15. In May, the department installed the overlay on both the north-and southbound lanes of the 765-foot-long concrete decks of the twin Johnson Creek Bridges. The project represents a typical installation, which includes:
Safety Plus Protection
- Surface preparation that cleans off oil and contaminants, including surface repair if needed.
- Shot-blasting concrete surfaces to an ICRI level of 5 to 7 to roughen up the surface and ensure a good chemical bond.
- Crews mix and prepare the epoxy, then manually spread it with squeegees. The aggregate is immediately broadcast across the surface with a shovel.
- Overlay is applied in two applications for road and bridge projects, versus one application for commercial and airport uses.
- The epoxy cures for seven to eight hours depending on temperatures.
- Loose rock is scraped off and vacuumed up by a sweeper truck, followed by leaf blowers.
- The surface is reopened to traffic.
Improved traction year-round is one of the immediate benefits motorists crossing the Route 15 bridges should experience following the overlay installation.
Studies at multiple overlay installation sites found surface friction immediately after installation measuring 58 to 60 using the ASTM E 524 bald tire skid test. On this test, the higher the number, the better the friction; generally, any skid number of more than 40 is considered acceptable. By providing increased friction, the overlay can reduce traffic delays for drivers and help avoid the expense of highway shutdowns due to weather conditions that make roads impassable.
Come winter, motorists will also benefit from enhanced safety during potential icing conditions, should the overlay's performance on the Route 15 Bridges match that of other test sites (see side-bar on page 42).
While greater safety and mobility provide the most immediate benefits of the overlay, in the long run its ability to extend the life of roads and bridges may prove to be as important an asset. The United States spends billions annually to preserve and maintain bridges, but it hasn't been enough to stem the tide of infrastructure decay.
For three decades, transportation departments have been using standard epoxy overlays to minimize water seepage and intrusion of corrosive agents like chlorides. The Virginia Transportation Research Council's Michael Sprinkel—a national expert in the design, construction, and evaluation of epoxy overlays—notes that the Safe-Lane overlay provides all the benefits of standard epoxy overlays. “However,” he says, “the specific aggregate-chemical combination in SafeLane has the additional benefit of minimizing snow and ice-related crashes as well.”
In the future, Shane Winner, assistant construction engineer of PennDOT District 3, would like to see a comparative study between the overlay and the latex-modified concrete overlays the district has used in the past, which he says are more labor-intensive and expensive than SafeLane.
Should the technology meet Penn-DOT's expectations, North Central Pennsylvania may become known not only for its premier fly-fishing. It may also be seen as a trail-blazer in the use of innovative transportation solutions.
— Persichetti is general manager of Cargill SafeLane Surface Overlay.
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