Traffic moves along Douglas County Road 1061 as it crosses over Kansas Highway 10.

Douglas County is looking into using an increasingly popular pavement-sealing technology to extend the lives of its bridges – while boosting cost efficiency, reducing traffic delays and giving tires a better surface to hold onto.

An added bonus: Drivers might even be able to turn down the radio, or lower their voices when talking to passengers in the back seat.

“It’s very smooth and quiet,” said Dave Meggers, research development engineer for the Kansas Department of Transportation. “We don’t tend to get the noise off it, because it’s an irregular surface. You don’t build up the harmonic noise that you have with typical pavement.”

The sound of relative silence is only one of several features of the sealant – formally known as a multicoat polymer overlay – that recently covered four bridges along Kansas Highway 10 in Douglas County.

Those projects, paid for and administered by the state’s department of transportation, are giving county engineers reason to look at the process for their own work.

With dozens of rural bridges in line for surface upgrades in coming years, the proximity of state projects could make the work more affordable, said Terese Gorman, engineering division manager.

“It’s another option for us,” she said. “It’s a choice, and it’s a cost comparison that can be made. With KDOT doing so much, then it could become more cost competitive in this area.”

The state already has put the surface on 100 bridges, and plans to continue adding more as the department’s maintenance schedule – and budget – allows, Meggers said.

The state has about 5,000 bridges, while cities and counties have more than another 20,000 – a grand total that ranks Kansas third in the nation in terms of the number of bridges on roads and highways, Meggers said.

Perhaps it’s no wonder, then, that the search for an optimal bridge surface continues.

The polymer overlay’s basic technology actually surfaced in the 1970s, but its use waned because of an underlying problem, Meggers said: People doing the projects hadn’t been preparing bridge surfaces properly for the new coatings. Crews had been using high-pressure water to scrub away oil, dirt, crumbled rocks and other materials that otherwise would keep the coating from forming a seal.

“It failed miserably,” Meggers said. “They didn’t clear the decks properly.”

Since then engineers have embraced the coatings once again, only now they are sure to have the bridge decks cleared by shotblasting – a cleaning process that shoots thousands of tiny metal pellets at the road surface, ripping away the top layer and all its imperfections for removal.

Crews then cover the pristine bridge surface with an epoxy, followed by a layer of small, angular flint chips. Next comes another coating of epoxy, plus another layer of grip-enhancing rocks.

The new coating forms a waterproof seal across the entire bridge deck, often running up onto the sides of guardrails so that moisture and other materials cannot seep into the cracks of the deck.

That’s key, Meggers said, because bridge decks are heavy, cost lots of money to replace and contain plenty of metal. Keeping moisture away helps prevent rust, stress and other problems that can lead to high-cost repairs or premature replacements.

Besides, Meggers said, applying the polymer-and-rock coating might take four or five days for a typical project, compared with two or three weeks for a traditional overlay. The polymer cures in four hours, rather than the week necessary with other methods.

“Here, we’re done in a week,” he said. “That’s much better, in terms of the user cost.”

Mike Perkins, operations manager for public works in the county, oversees crews who typically put an acrylic-based sealant on the county’s 162 bridges once every two or three years – an upgrade from the previous process, using linseed oil.

But that’s a short-term approach. Among bridges on the list for more significant work is one on Wells Overlook Road, which is Douglas County Road 458 just east of U.S. Highway 59.

After watching crews earlier this year apply a polymer coating on a bridge connecting Kansas Highway 7 and the Kansas Turnpike, Perkins is looking forward to exploring options for using the process on county bridges.

“I think there are some real possibilities for it,” he said.