Archive for Tuesday, October 21, 2008

Thin is in for highway repavings

October 21, 2008


New pavement on state highways is getting thinner, harder and less time-consuming to apply.

And with each fresh placement of the NovaChip surface, engineers are embracing a welcome side benefit: new holes in the road - thousands upon thousands of tiny openings - that help improve traffic safety.

"The water does have a place to escape," said Rick Barezinsky, Kansas Department of Transportation field materials engineer. "We do have less spray - when you're following a truck, there's less spray."

The department is rolling out the new surface with increased regularity, expanding the reach of its real-life road tests to assess performance, cost-effectiveness and other factors when compared with traditional repaving methods and materials.

The NovaChip surface - the brand name for what engineers call an "ultrathin wearing course," or "ultrathin bonded asphalt surface" - is a modified version of traditional "hot mix" pavement. Unlike typical overlays, which can range from an inch to 1.5 inches thick, the thinner surface ranges from 5/8 inch to 3/4 inch thick.

That may not sound like much of a difference, but for engineers concerned about drainage profiles and height clearances under bridges, every bit counts, Barezinsky said. The thinner surfaces also cover less area, as they typically don't need to extend onto roadside shoulders.

Then there's scheduling. A traditional hot mix overlay can be installed at a rate of three miles a day, Barezinsky said, and that's on a "great" day.

The thinner surface goes down twice as fast, meaning less time for arrow boards, orange cones and merging drivers on affected roadways.

"This stuff can be placed as much as six miles in a day," said Barezinsky, who chuckles when recalling his on-site observations of the process in practice. "You jog along with the paver. It goes down fairly quickly."

The process isn't without its drawbacks. The system requires harder-than-normal aggregate, which costs more, and the emulsion membrane - the sticky, sealing material that holds the rock in place and seals cracks in the road below - also isn't cheap, he said.

But by covering less area, and with rock options becoming more economical, the cost comparison is about break even, Barezinsky said.

Now it's a matter of performance. The department's first NovaChip surface came in 2002, when applied on Shawnee Mission Parkway on the way to and from the Plaza in Kansas City, Mo.

Since then the thinner material has found its way onto stretches of Kansas Highway 10 in Johnson County, and more areas are being considered for future projects.

Engineers are looking for the "niche" where the thin pavement works best, said Rick Kreider, the department's bureau chief for materials and research.

"These (products) all have their boundaries," he said. "If you don't explore a little bit, you don't know where the niche really begins or ends."


gccs14r 9 years, 1 month ago

What's it do to tire wear? If it's a harder, more angular aggregate, is it then a State-sponsored tire shredder? How much will that cost us in the long run?

Curtis Lange 9 years, 1 month ago

Wouldn't more holes in the roadway increase pothole chances during the winter months? Damned if you do, damned if you don't.

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