Results are in for the first phase of field tests at the National Center for Asphalt Technology at Auburn University in Alabama and states are crowing about the results. "They show if we can control quality during construction then we can solve most of our problems," says E. Ray Brown, civil engineering professor and center director.
|LOTSA LAPS Trucks made 1 million passes, yielding 15 years of data in two years. (photo courtesy of Auburn University)|
The center's goal when it opened the test track in 2000 was to provide practical research for individual state departments of transportation, which in the past had only fragmented results, says Don Brock, chairman and CEO of Astec Industries, Chattanooga, Tenn., and member of the center's board of directors. States get results in two years; a typical interval on a highway test section is 15. Four trucks made 1 million passes on the 1.7-mile-long test track in rural Alabama to achieve 9 million equivalent 18,000-lb single axle loads (ESAL). The track has 46 200-ft-long asphalt test sections, 24 in the straightaways. The 22 curved sections had similar results as the more desirable straightaways.
Alabama put up $3.5 million to build the track and nine state departments of transportation sponsored at least two sections at a cost of $250,000 each. The states determined what they wanted tested and shipped rock and asphalt mixes to the site. "This is not a typical shared research project. It is a research co-op. Each state is my boss on their sections," says Raymond "Buzz" Powell, project manager. The National Asphalt Paving Association invested $9.8 million, but has an arms-length relationship to keep test results objective and credible, says Mike Acott, president.
|MANY BOSSES Powell works for nine state DOTs. (photo courtesy of Auburn University)|
The states wanted to test performance. "About one-third of our highway budget goes for hot-mix asphalt. We wanted our research dollars to show us where to put our construction money," says Larry Lockett, Alabama DOT materials and tests engineer. The agency learned that increasing the limestone in its aggregate mix polishes or slickens the surface. "We have lots of limestone, but we're losing our source of river gravel," says Lockett. Tests also showed that good mixes can be made from all aggregate choices, which is helpful to states like Mississippi, with only one choice.
Indiana researchers wanted to find a relationship between lab and field performance tests. "We got really good agreement and we're excited about that," says John Haddock, assistant engineering professor at Purdue University.
Indiana and South Carolina wanted to test whether superpave's coarse mix or fine mix were more rut-resistant. Both performed the same, debunking the widely held belief that coarse mix performs better. South Carolina plans to test its sections for another 10 million EASLs, says Chad Hawkins, state asphalt engineer. Two more sections in the next phase will tell SCDOT about the performance and constructibility of stone matrix asphalt.
Tests that show which mixes reduce noise best will end in mid-December, with results to be published by February.
One major plus is that states share information. Each week the sections are tested for rutting, skidding, temperature and other variables. Results are posted on the Website www.pavetrack.com, where each state can see the performance of its section and the performance of other states' sections.
Covenant Transportation, Chattanooga, Tenn., provided trucks and drivers and tested engines, tires and transmissions. Results showed that smooth roads reduce fuel consumption by 5%, and reduce tire wear, maintenance and driver fatigue.