County tests new paving treatment

EVERETT — Snohomish County is taking the lead on a new approach to paving that could result in cheaper, faster and better upgrades to local roadways.

It’s called “ultra thin bonded wearing course” — and while it won’t do any heavy lifting, it’s already been put to use on roads needing minor fixes for cracks and raveling.

“We’ve been investigating ways to stretch our preservation dollars for quite a number of years now, and this is one of the methods that we thought showed a lot of promise,” said Doug McCormick, a Snohomish County engineering manager who oversees the paving program. “It’s a way of preserving the road but with less dollars than a traditional overlay.”

The treatment is a classy upgrade from the usual chip seal, which city folk often find to be too rough, and which also carries the potential for flying chips of rock.

And it is, in theory, a more durable and longer-lasting alternative than the more frequently used methods of hot-mix asphalt overlays.

It’s one reason the Washington State Department of Transportation in 2001 decided to test the treatment (under the trademark NovaChip name) on a section of Highway 17 in Soap Lake. A six-year study of its effects showed the treatment was effective in reducing both the frequency and severity of cracking. And it made for a smoother ride, too.

But not much has been done with the process since then.

Snohomish County believes its efforts this summer — in conjunction with the cities of Mill Creek, Mukilteo and Marysville — is a first for the region.

It’s a small start. In all, 6.5 miles of roadway received the new treatment, out of 105 miles of summer road repairs.

“It’s a new technology, new method we’re trying to introduce to the area,” McCormick said.

The method was developed in France in 1986, according to a Federal Highway Administration brief. In the United States, use dates to the 1990s but didn’t pick up for another decade.

Research from other states indicate pavement life expectancies of between five and 12 years depending on what the treatment is covering up and local conditions, such as weather.

The treatment results in reportedly quieter pavement, and it also drains better, meaning less spray kicked up by tires.

And, yes, it is “ultra thin.”

Part of the cost savings comes in less material. The “ultra thin” overlay is three-quarter-inch thick, while a normal overlay depth in Snohomish County is 2 inches.

Savings also come in the quick turn-around, thanks to special machinery that applies a finishing coat immediately after a first tack-like coat.

“The road is open back to traffic fairly quickly — like 20 minutes — where with a typical overlay you’re talking 2 hours,” McCormick said. That means less traffic control and flagging expenses.

The apparatus wasn’t available locally, which added some costs to the county’s initial foray.

But the county still expects savings overall.

Estimates put cost savings at about $10,000 per mile compared to a more typical overlay, said Joyce Barnes, a pavement management engineer with the county.

“Right now we fully expect to use it again,” McCormick said.

The future could see other experiments.

There’s a method that involves recycling part of the old roadway. The hot-in-place method “removes a portion of the existing asphalt roadway surface and mixes it with new emulsion (the sticky black stuff) to rejuvenate the material and then places it back down on the roadway,” McCormick said.

There’s also a warm mix asphalt method that lowers the temperature of the asphalt as it’s placed, leading to fewer emissions and better compaction, Barnes added.

The machinery used for both methods, however, is even more cumbersome than that needed for an “ultra thin” overlay. And like the “ultra thin” application, only certain roads would be candidates.

For a list of roads that received the “ultra thin” treatment this summer, see the Street Smarts blog at www.heraldnet.com.

Roads where the ultra thin bonded wearing course was placed (cities paid for work in city limits):

Mill Creek:

Silver Crest Drive (28th Drive SE to 35th Avenue SE)

139th Place SE (28th Drive SE to cul de sac)

139th Place SE (27th Drive SE to 28th Drive SE)

138th Street SE (Silver Crest Drive to 32nd Drive SE)

32nd Drive SE (138th Street SE to Silver Crest Drive)

30th Drive SE (Silver Crest Drive to cul de sac)

28th Drive SE (139th Place SE to cul de sac)

27th Drive SE (139th Place SE to Silver Crest Drive)

Mukilteo: