The newest innovation in asphalt mix has everyone talking in Arizona, from drivers on the interstate to transportation department officials. The state has started regularly using an asphalt rubber overlay to resurface roads. The technique reduces road noise by 78 percent.
Since 1988, Arizona has paved one-third of its roads with asphalt rubber. The mix constitutes 15 to 20 percent ground rubber, which not only reduces the noise of cars on the road but also cracking in the pavement surface. Because of the rubber’s flexibility, underlying cracks on old pavement are less likely to come through the overlay than they would with traditional asphalt mix.
Eventually, asphalt rubber will crack, but tests are still being run to find out how long the rubber pavement will last. The Arizona transportation department has been monitoring its first non-experimental asphalt rubber overlay on Interstate 19, which was paved 15 years ago. In 2001, only 1 percent of the surface had cracked, and the annual maintenance was running at $50 per lane mile.
Several other Southern and Western states, including California, Florida and Texas, routinely use asphalt rubber for overlays. Many contractors, however, have been critical and suspicious of asphalt rubber. Conventional asphalt is seen as a more comfortable, reliable solution that is more cost-effective for the short term. Because asphalt rubber costs more, many DOTS with tight budgets will choose the traditional mix.
New Mexico’s state highway and transportation department had originally planned on paving a 112-lane-mile stretch on U.S. 54 with conventional asphalt. But FNF Construction of Tempe, Ariz. persuaded the department to use the project to test asphalt rubber. To help the DOT’s test, Ford donated old Bridgestone/Firestone tires that had been recalled in 2001. Ford paid the cost of processing the asphalt rubber. New Mexico therefore got the asphalt rubber test surface for the cost of a conventional asphalt pavement.
Asphalt rubber isn’t for all jobs, but some jobs call for it despite its higher cost. Pavement that has extreme cracking or requires total rehab can cost more than $200,000 per lane mile. An asphalt rubber overlay, however, could hold the road together long term for one-fourth the price of rehabbing the road.
Laying asphalt rubber is different from paving with conventional asphalt in that heat is a major concern in the mixing process. Because of the rubber content in asphalt rubber, the heat should be controlled to prevent smoke. Another difference involves rollers. Pneumatic rollers cannot be used to lay asphalt rubber because the rubber tires pick up the rubber in the asphalt. Steel-wheeled machines handle the compaction instead.
