Bridge number 5961 was a 120 foot-long problem. Steam on the river and from a nearby paper mill result in an icy bridge deck when the cold air hits, causing accidents. And with almost 6,000 vehicles crossing the bridge daily, that’s a real problem.
NRRI researcher Larry Zanko offered a local solution—taconite tailings. This waste rock from the taconite pellet making process, is being tested in a new, high-friction bridge deck surface treatment on 5961 to improve its “grip-ability.” The bridge is on Highway 11, just east of International Falls, Minn.
“I’m looking forward to seeing how well this works through the winter snow plow season,” said Zanko. “Mn/DOT will be watching it closely and we’ll evaluate its wear characteristics, but I expect this to work well.”
Extensive NRRI research on taconite waste rock as an aggregate product is proving valuable for road repair projects and, in this case, increased driver safety. Tailings offer a long list of benefits: it’s already blasted and crushed, it’s hard and angular, and it’s dark-colored so it absorbs solar heat to help melt snow and ice.
“Our goal is to find value-added uses and markets for taconite aggregate since it’s readily available on the Iron Range, and a project like this helps us do that,” said Zanko.
The aggregate adheres to the bridge surface with AccuFlex, a castor oil-based road repair compound made by a locally owned company. It cures within a couple of hours, and is odorless, durable, and environmentally friendly.
“Normally we use fractured flint from Oklahoma for bridge decks,” explained AccuFlex CFO Gordy Carlson. “It’s very hard and angular, similar to taconite tailings. But flint is light in color. Because the tailings are dark, they’ll absorb solar energy to melt snow and ice, which is great in this part of the country.”
An added bonus, of course, is not trucking rock thousands of miles.
A similar demonstration project on a slippery bridge in Colorado three years ago is holding up well, Zanko said.
“On that first project, we learned how important the prep work is before the application. We also know that dry conditions are required when we apply the coating and the rock,” he said.
Mn/DOT bridge engineer Pat Huston said they’ll talk with the plow drivers and watch how well the product holds up. They’ll also keep track of any accidents to compare whether or not the new bridge deck increased safety.
“This is a homegrown product, so that’s good,” said Huston. “And for such a remote bridge, I was surprised at how much traffic is on it. We’ll watch it, and hopefully we’ll see a decrease in accidents.”