MISSISSAUGA, Ontario—Rubber-modified asphalt not only works but can no longer be labeled a ``new'' technology, according to asphalt-rubber experts. There is enough evidence now to demonstrate the product's absolute value in lengthening pavement life, giving a smoother ride and dampening road noise, these experts said at ``Rubber Recycling '98: The North American Experience,'' a fall conference held in Mississauga.
The rubberized asphalt experiences of a county in Canada and the state of Arizona demonstrate that contention.
Grey County, about 100 miles north of Toronto on Lake Huron's Georgian Bay, began its system in 1991 to try and clean up 28,000 tires landfilled within its borders, according to Gary Shaw, manager of the Grey County Highways Department.
``Our local government was very supportive,'' Mr. Shaw said at the conference. ``We received (about $1.3 million) for different pilot programs.''
But the government insisted on ambient-ground rubber instead of the cryogenic grinding prevalent in Ontario, so at first Mr. Shaw had to ship the tires to Long Island for grinding.
Persuading the provincial government of Ontario was even tougher.
``We had to prove to the Ministry of Environment that we weren't solving one problem by creating another,'' Mr. Shaw said.
At first, Grey County used the generic dry process of asphalt rubber created by Barry Takallou, a Los Angeles highway engineer. ``I read about the work he'd done in Alaska,'' Mr. Shaw said.
But later the county switched to a unique combination wet-dry process which produces ``a very black, sticky and spongy asphalt.''
In its highway projects, the county tries to lay conventional asphalt and asphalt rubber side by side to compare performance. In every case, the asphalt rubber has reduced not only pavement cracking, but also stopping distance, driving noise and winter salt requirements, according to Mr. Shaw.
Cheaper asphalt is another benefit of the closed-loop program, because Grey County now grinds its own crumb rubber and sends it to the asphalt supplier. The savings pay for the cost of crumbing the tires, Mr. Shaw said.
Grey County charges $2.50 per each new tire sold to pay for the closed-loop program. At 60,000 tires sold in Grey County annually—about one per county resident—that generates about $97,170 annually for the program.
For its innovative program, Grey County won an award last year from the Asphalt Recycling and Reclaiming Association. Mr. Shaw also receives calls from across North America about the county's asphalt rubber technology, but not its closed-loop recycling system.
``I don't know of anyone in Canada who's doing what we're doing,'' he said.
Arizona's experience with asphalt rubber goes back to the 1960s. At that time, the state began using Charles McDonald's wet-process asphalt rubber for ``Band-Aid'' chip-seal applications, according to Gary Hicks, professor emeritus of civil engineering at Oregon State University.
Arizona's experience is living proof of the cost-effectiveness of asphalt rubber, according to George Way, pavement design engineer for the Arizona Department of Transportation.
Arizona is a good test case for asphalt rubber, Mr. Way said. It has not only the hot, dry ambience of the desert but also the extreme winter conditions of the mountains around Flagstaff, where temperatures fall as low as minus 29 degrees Celsius and snowfalls reach 100 inches annually.
The state built several test sections on Interstate 40 near Flagstaff in 1990, using both conventional asphalt and asphalt rubber.
``The conventional asphalt cracked the first winter and continued to crack,'' Mr. Way said. But on an asphalt rubber section near the conventional asphalt, ``we can verify that very few cracks have occurred to this day—most of them in the shoulder, where you don't get traffic.''
High prices for asphalt rubber—about $500 a ton—were the only thing that kept Arizona from using the material more extensively. But when the patent on the process lapsed in the early 1990s, prices fell by half and the cost-effectiveness grew exponentially, Mr. Way said.
Since 1988, Arizona has laid about 1,100 miles of asphalt rubber pavement, using about 5.5 million tires, he said. He expects the state to reach 2,000 miles in the next few years.
``Arizona,'' Mr. Way concluded, ``is the state where the rubber meets the rubber.''
A federal government-sponsored life-cycle cost analysis was completed in 1994 at the University of Florida, surveying current manufacturing and road-building practices using asphalt rubber. That set the stage for the latest investigation, performed by Mr. Hicks and others at Oregon State.
Budget cuts canceled the government's sponsorship, but the Rubber Pavements Association put up the money to finish the report, Mr. Hicks said.
Many factors are included in figuring life-cycle cost analyses, including agency costs, user costs, the expenditure stream and the complete present value, Mr. Hicks said.
But there are only two ways of calculating life-cycle costs: the deterministic, which assigns fixed values to all calculations and costs, and probabilistic, which considers variables and ``allows you to bring in an element of risk,'' he said.
In the preliminary numbers for the latest study, while the deterministic life-cycle method demonstrates some benefit to using asphalt rubber, the probabilistic model shows the material to be cost-effective more than 80 percent of the time, according to Mr. Hicks.
``Asphalt rubber needs to be evaluated using life-cycle cost analyses,'' he said. ``Where it's not cost-effective, it shouldn't be used. But for the sites we've looked at, it's proven to be cost-effective under most circumstances.''