Ten rutted miles of Interstate 90 will be repaved this summer because asphalt put down in 1991 lasted only half as long as expected.
The work, between Pines Road in the Spokane Valley and the Idaho border, will cost about $1.3 million. The original paving was part of a large package of I-90 improvements that cost $3.3 million.
Acme Materials and Construction Co., which also did the 1991 paving, is expected to begin work Aug. 14 and has 45 days to finish the job. Lanes in both directions will be closed at times and traffic will be delayed.
Asphalt laid on well-used portions of I-90 normally lasts at least eight years, said Guy Gibson of the state Department of Transportation’s Spokane material lab. The life expectancy is longer - up to 18 years - in more rural areas.
For the 1991 project, Acme followed state specifications, which called for “open grade” asphalt, a porous mix used to control tire spray. The mix uses smaller gravel than typical asphalt, is applied in a thinner layer and offers quieter, smoother, safer driving, especially during rainstorms.
Specifications this time call for standard asphalt.
The open grade asphalt didn’t hold up to the Spokane Valley’s heavy traffic. Studded tires tore into the dry pavement, causing deep ruts; frequent freezing and thawing made matters worse.
In fact, pavement engineer Robyn Moore of the state DOT said open grade asphalt performed worse than expected most places it was applied. It no longer is used in Washington, he said.
“We’re seeing some of the same problems over here (in Western Washington). Maybe not as severe.”
What’s more, the water control advantage of the porous pavement lasts only a few years, until the pores fill in with sand and other debris, said Moore.
He didn’t know how many miles of the state’s highways are paved with open grade asphalt.
“It’s a fairly small percentage of our overall asphalt paving program,” he said.
Gibson said the asphalt was used on I-90 near the town of Sprague, but was replaced several years ago. There, it held up better, lasting about 10 years.
Several times since 1969, when studded tires were approved for use in Washington, the Legislature has considered banning the tires because they are tough on pavement. Each attempt has failed, although the tires, which improve traction on ice, can only be used in winter.
Ruts recently ground out of a section of I-90 between Spokane and the Sprague Avenue interchange are not related to the problem, Gibson said. That section is made of concrete and is much older than the pavement east of Pines.
Gibson said it’s a common misconception that heavy trucks caused the ruts. Actually, he said, truck axles are wider than the ruts, which are a good fit for most passenger cars.