Not Slippery When Wet:Anti-Ice Coating Hits The Road
There’s a bridge along Wisconsin’s Highway 8 that’s notorious for ice and bad wrecks. But this winter, no one has spun out and slammed into the guardrails above the Wolf River, and officials say that’s no accident.
Last summer, workers installed a new surface on the 120-foot span, located about six miles west of the small town of Crandon, Wis. Developed by a researcher at Michigan Technological University, this anti-icing pavement overlay is a sheet of epoxy covered with an aggregate. From the top, it looks like kitty litter. A cross section looks more like toffee covered with lots of chopped nuts.
“It acts sort of like a hard sponge,” says inventor Russ Alger, a project manager/research leader at MTU’s Keweenaw Research Center. “You put a light amount of de-icing chemical on there, and it keeps coming up to the surface.”
Thus, when salt trucks apply magnesium chloride to the bridge, it doesn’t just sit on top of the concrete, to be pushed off by snow plows or washed into the river. It soaks into the overlay and stays put.
This reduces runoff into the river, and it can save money. “You don’t have to use very much chemical, and you don’t have to apply it very often,” Alger says.
When the time came to test the overlay, Alger approached the Wisconsin Department of Transportation, which has no shortage of treacherous roadways, especially in the north. “They told me, ‘We’re going to give you the worst bridge in the state,'” Alger recalls. “It had the highest accident rate and the worst frost and ice.”
The bridge crosses a river that gives off a lot of steam, which condenses and freezes on the pavement. Plus, it’s midway up a steep hill.
Motorists come barreling up Wolf River Hill with their cruise control set on 60 mph. “If you are accelerating and your tires hit that ice, you are off to the races,” observes Ron Cole, patrol superintendent of the Forest County Highway Department.
As a result, Cole has received more than one 3 a.m. call from state police asking him to send a salt truck out to the bridge, which has seen five accidents in the past two years.
However, with the anti-icing overlay coating the pavement, his phone has been quiet. There have been no accidents so far this winter, and crews have applied magnesium chloride to the bridge only five times, fewer than half the typical number.
“One time I was out there, and the bridge was white on both sides and wet in the middle,” Cole said. “It’s been a success in my mind.”
Alger hopes that the Wolf River Bridge success will be repeated elsewhere. Michigan Tech is negotiating a licensing agreement with a large corporation to use the anti-icing pavement overlay, and plans are under way to install it this summer on a number of accident-prone sites across the Midwest.
If the Wolf River Bridge trial is any indication, highway departments will see the cost of treating their trouble spots plummet, and drivers will make fewer trips to the body shop–and to the hospital.