A Scrappy Stretch of Road : It’s Made of a Mixture of Asphalt and Rubber From Recycled Tires
Right next to Chi-Chi’s Restaurant in Santa Clarita, near the intersection of Soledad Canyon and Bouquet Canyon roads, there is a section of street where the rubber really meets the road.
The half-mile stretch of Soledad Canyon Road looks like any other road in the area except that it has been paved with asphalt rubber, a combination of conventional asphalt and rubber made from ground-up scrap tires.
Thousand Oaks, Ventura, Anaheim, Arcadia and several other Southern California cities have laid down the rubber, using hundreds of thousands of old tires in repaving projects, adding to the 3,000 miles of state roads that have received the treatment.
It seems like an environmentalist’s dream: Instead of getting junked in the area’s shrinking landfills, the tires are mixed with asphalt to create a paving material that holds up twice as long as conventional asphalt.
Although reviews by state and local officials have been generally positive, questions remain. Some transportation officials fear that the material has not been adequately tested. There is no conclusive evidence that asphalt rubber can be recycled after it deteriorates, as conventional asphalt can. And there is concern whether the process of heating and laying the material gives off more toxic fumes than conventional methods.
Another issue is the cost, which is twice that of standard asphalt. Even though tests indicate that roads repaved with the mixture could last twice as long, allowing it to be applied more sparingly and reducing the overall cost, not everyone believes that the material’s greater expense is justified.
Only a handful of companies--just one in California--have licenses to make the patented key ingredient in the product, generating criticism from some who say the price would be lower if there was more competition.
Despite such concerns, the California Department of Transportation in February removed the material’s experimental designation and approved guidelines for its use. Last year, federal legislation was adopted requiring the asphalt in federally funded projects to contain at least 5% rubber by 1994. The required percentage is to increase to 20% by 1997.
But long before paving with an asphalt-rubber mix was officially backed by state and federal authorities, cities throughout Southern California were experimenting with it.
Asphalt rubber is considered less permeable that conventional asphalt and therefore not as susceptible to cracks and potholes caused by rain and freezing temperatures. In addition, roads paved with it are slightly darker and smoother and some road construction officials believe that the rubber in the pavement provides for a quieter ride and better traction.
“I find a difference,” said Tom Pizza, a principal civil engineer with Thousand Oaks. “To me it feels a little bit smoother and quieter.”
But Caltrans officials have not tested the rubber-laced surfaces to determine whether they make the ride quieter or improve traction.
One indisputable benefit is that asphalt-rubber roads provide another way to recycle used tires and other scrap rubber that would otherwise end up in landfills. In total, 14.7 million pounds of ground rubber--the equivalent of more than 2 million tires--were used between 1983 and 1989 throughout California.
In Southern California, Santa Clarita has used 51,729 recycled tires to pave nearly four miles of streets; it plans to pave another three miles this summer, using another 34,700 tires. Last summer, Thousand Oaks used 177,000 tires to pave about 30 miles of streets.
Los Angeles tried asphalt rubber more than 10 years ago on a section of Olympic Boulevard but has not used it since.
Patrick Howard, director of the Bureau of Street Maintenance, said asphalt rubber is not considered cost-effective. He said the city has its own asphalt-making facilities and would have to make expensive improvements to equipment to include rubber.
The city recycles most of its asphalt by reconstituting it in a microwave processor and is recycling glass by mixing it with some of the asphalt, he said.
“I think we are not at a point yet where we can say that the cost is offset by the properties that rubberized asphalt is supposed to have,” Howard said.
Even though Santa Clarita is ahead of other cities in using and testing the material, civil engineer Kit Nell said the material is being used sparingly and that only half-mile stretches have been paved with it. “We didn’t want to blindly jump on the bandwagon,” he said.
Despite its growing use, asphalt rubber barely makes a dent in the 3-billion tires piled in legal and illegal dumps nationwide. Each year, another 250 million tires are discarded and 85% wind up in landfills.
“Clearly . . . any product’s use that reduces reliance on landfills is important . . . even if it is by a small amount,” said Joan Edwards, director of Los Angeles’ Integrated Solid Waste Management Office.
Donna J. Carlson, spokeswoman for Manhole Adjusting Inc. of Monterey Park, the only California-based firm licensed to produce the patented material used to make asphalt rubber, said its durability and ecological benefits make it the paving product of the future.
“If you paved 5% of all roads in California with a two-inch overlay of asphalt rubber you can use up all the tires” that are thrown away in the state each year, she said.
Tire rubber can be used on streets in a number of ways. But the most common method is called asphalt-rubber hot mix, in which the rubber is pulverized to the size of coffee grounds and blended with the hot asphalt in a mix of 25% rubber, 75% asphalt. That mix, known as a binder, is combined with gravel aggregate and applied with conventional paving equipment.
Jack Van Kirk, a senior material and research engineer for Caltrans and one of the state’s leading experts on asphalt rubber, said although he sees many benefits from its use he would have preferred to conduct more tests on the material’s capacity for reuse before the state guidelines were adopted.
He said the rubber industry and tire granulator manufacturers helped rush adoption of the federal legislation requiring the use of rubber, spurring the state to move ahead more quickly.
Carlson said there was no pressure put on Congress to adopt the legislation. And she criticized Caltrans for failing to test asphalt rubber sooner. She also said the company’s research has not turned up any problems with increased toxic emissions. A spokeswoman for the South Coast Air Quality Management District said the company has never been cited for emissions violations.
“Quite frankly, if we waited for government to do this we would be in the year 2000 and still not have all the answers,” Carlson said.