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Testing Quieter Asphalt

WSDOT Will Monitor How Two Types Hold Up on Busy Stretch of I-5

Story by Carl Molesworth -- Pacific Builder and Engineer, 12/4/2006

Motorists traveling southbound on Interstate 5 between Everett, Wash., and Seattle have begun enjoying an 8.5-mile respite from the rutted, worn roadway surface in the Lynnwood area, thanks to a paving project recently completed for the Washington State Department of Transportation.

The Everett office of Wilder Construction Co. (see related story starting on Page 4) served as general contractor for the $8.1-million project. Starting in June, Wilder's crews ground down and repaved 8.5 miles of southbound I-5 from State Route 526 in Everett to 52nd Avenue West in Lynnwood. They also repaved the Swamp Creek interchange, and improved the 44th Avenue West interchange in Lynnwood by repaving the existing ramps, extending the on-ramp to southbound I-5, upgrading lighting, and adding guardrail.

An important element of the job was a 1.8-mile test section with two types of quieter pavement between Swamp Creek and 44th Avenue West in Lynnwood. Quieter pavement is made of materials that help reduce the amount of highway noise generated by the tires of traveling vehicles. Over the next five years, WSDOT engineers will study this section of roadway to see if quieter pavement can stand up to ever-changing driving conditions in the Pacific Northwest.

According to WSDOT, the two types of quiet asphalt used in the test were Open Graded Friction Course and Open Graded Friction Course Asphalt-Rubber. OGFC consists of a mixture of asphalt, mineral aggregate, mineral filler, and other additives. Asphalt binder material for the OGFC is PG 70-22. SBS modifier is added to the neat asphalt to produce a binder that complies with the requirements. Meanwhile, OGFC-AR contains a mixture of rubberized asphalt, mineral aggregate, mineral filler, and other additives. The asphalt binder is PG 58-22 or PG 64-22.

Although quieter pavements are used in many dry, warm states such as Arizona, California and Texas, WSDOT engineers want to make sure the pavement can stand up to the Northwest's unusual driving climate.

Operating mostly at night because of the high traffic volumes on this stretch of I-5 during the daytime, Wilder's crews worked their way southward from the north end of the project. This also allowed them to schedule the paving of the test section during mid-August, when temperatures and weather would likely be closest to ideal.

It didn't quite work out that way, however. A key piece of equipment failed during paving of the test section on the weekend of Aug. 26–27. The project team decided to take a calculated risk and continue paving without it. But after it was finished, irregularities and bumps on the surface were noted on a one-mile-long section in the right center lane of the freeway.

The OGFC surface in question did not meet WSDOT and Wilder Construction's standards for smoothness and durability. As such, this section of pavement had to be removed and replaced at Wilder Construction's expense. Weather and other factors intervened, but about 300 tons of the polymer-modified asphalt finally was laid on the night of Oct. 5 to complete the paving.

"We're really pleased to finish paving this season," said WSDOT Project Engineer Marlin Lenssen. "Wilder pushed hard to get this work done so drivers could enjoy a smoother, safer ride on I-5. We were also very fortunate that the weather cooperated."

Through December, crews are adding the finishing touches to the project, including permanent striping, guardrail and signing.

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