91视频

Many of Portland鈥檚 streets are crumbling, and are pockmarked by divots and potholes. The city knows this, and is warming to a new paving technique that may help its roads last longer.

But it remains to be seen how well 鈥�warm-mix鈥� paving will hold up, and whether it鈥檚 worth a slightly higher cost.

鈥淲ho wants to take a (financial) hit if you put the (asphalt) down and it comes up in five years?鈥� said Ryan Gaylor, a construction manager at KF Jacobsen & Co. His company, which has been following warm-mix paving closely, is one of the largest paving contractors in Portland.

The state of Oregon is interested in the warm-mix technique, too, but said cost was a concern. The process requires use of a chemical additive, which costs between $1 and $2 per ton of pavement. Liz Hunt, a paving expert at the Oregon Department of Transportation, said the warm-mix technique 鈥渨arrants investigation.鈥�

Portland may become the state鈥檚 warm-mix paving pacesetter. The city has already used the technique on two projects. The first was on Northeast 122nd Avenue, between Burnside and Holladay streets, and the second was on Southeast 112th Avenue between Powell Boulevard and Market Street. The city will study the streets through winter to see how they hold up.

鈥淚n three to five years, it wouldn鈥檛 surprise me if people asked, 鈥榃hat was hot mix, and why did we ever use it?鈥欌�� said Steve Townsend, a street engineer with the city.

Jim Huddleston, executive director of the Asphalt Pavement Association of Oregon, said he believes the new technique makes roads last longer. That鈥檚 important in Portland and elsewhere, he added, because the number of motorists driving heavy vehicles, such as trucks and sports utility vehicles, has increased over the decade.

Those vehicles have pounded the city鈥檚 streets, Huddleston said. The Portland Bureau of Transportation, through its street preservation program, uses about 100,000 tons of asphalt to lay down about 50 miles of pavement each year.

But city audits have been critical of the bureau鈥檚 paving for years. The most recent audit, from 2006, stated that newly paved streets did not meet city standards.

Now, the Portland Bureau of Transportation has started testing the warm-mix paving technique, in which asphalt is mixed at temperatures 50 to 100 degrees cooler than the traditional hot-mix technique. Fewer noxious fumes are generated, and less natural gas is used with the warm-mix technique.

Using warm-mix also will allow the city to recycle more pavement material. With traditional asphalt, the city limits the amount of ground-up pavement rock to 30 percent of the overall mix. Using any more causes bonding problems.

With the warm-mix, however, recycled pavement can represent up to 50 percent of the mix, which would save money, Gaylor said.

Townsend said the task now is to spread the use of warm-mix. He doesn鈥檛 expect that to happen until more projects move ahead, and that will take time because the technique is new to the United States.

But warm-mix paving has been used in Europe for a decade. The Federal Highway Administration and the Asphalt Pavers Association of America brought the technique to the U.S. six years ago, Huddleston said.

However, warm-mix took years to trickle down to local jurisdictions because the European techniques were proprietary. Local agencies had to develop their own methods.

KF Jacobsen has been tracking the new paving technique. Gaylor said he thinks warm-mix is the future of paving, but he said it will be a hard sell to cash-strapped agencies such as the Oregon Department of Transportation.

Gaylor expects the technique to be used on more projects in the future, however, as it gains popularity elsewhere. Texas implemented warm-mix paving as the norm in 2008, and in the last year has used the technique on one million tons of asphalt.

In Oregon, Huddleston said, the state could use 150,000 tons of warm-mix asphalt. 鈥淚 lot of the workers would like it,鈥� he said. 鈥淚t would be a lot cooler to work around.鈥�