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Dense pavement makes driving more quiet

I really like the new blacktop between Ashland and Medford. What component was added to make it so quiet? And why didn't they put a layer of it on the bridges? Would it add too much weight?

— Jim, Ashland

The Oregon Department of Transportation is using a dense-grade mix of asphalt more often, including along that stretch of I-5, said ODOT spokesman Gary Leaming.

That compares to open-grade mix, which results in more aggregate at the top of the road surface, he said.

The dense-grade mix creates a smoother, flat surface, without the spaces between the gravel found on the surface of open-grade mix, Leaming said.

While many drivers appreciate how quiet the smooth surface is, dense-grade mix has other benefits.

"There's better traction. You don't have as much open space. It's more dense, so tires have more contact with pavement," Leaming said.

Open-grade mix is more subject to wear-and-tear, he said.

In the past, ODOT had to replace a section of open-grade paving along I-5 near Ashland because the roadway was getting chewed up when motorists put on chains to go over the Siskiyou Pass in winter.

"The chains would grab the aggregate. We saw a lot of rutting there," Leaming said.

A downside to the denser mix will be more water spraying up during rainy periods, he said.

Leaming said bridges weren't coated with asphalt because the extra layer isn't necessary.

"There's no need to put asphalt on a bridge if you have a good concrete deck. It does add weight," he said.

— Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to youasked@mailtribune.com. To see a collection of columns, go to mailtribune.com/youasked. We’re sorry, but the volume of questions received prevents us from answering all of them.