NCAT Pavement Test Track
Western Hemisphere’s Most Ambitious Asphalt Research Facility
Inducted in 2003
Over ninety percent of American paved roadways have surfaces made of hot-mix asphalt. And yet, American civil engineers faced the new millennium unable to fully test innovations in hot-mix asphalt design. Enter NCAT, the National Center for Asphalt Technology, formed at Auburn University in 1986 by AU and the National Asphalt Pavement Association. NCAT’s mission is improving pavements, a valuable service: lengthening pavement life by just ten percent saves two billion U.S. dollars annually. Close to the university, on 309 acres and boasting a 1.7-mile track, research quarters, weather station, and asphalt plant, NCAT is pursuing its mission. At the NCAT Pavement Test Track, designers can subject surfaces in just two years to a load equaling a decade of busy interstate traffic. The track thus allows pavement innovations to be tested on real-world terms, in workable periods of time.
The highly anticipated $7.5 million test track opened in late 2000. Its 32-foot-wide paved surface was installed using premier paving equipment. Only the oval’s outer lane carries traffic, which in the initial two-year research period comprised four trucks, each pulling three weighted trailers at 45 m.p.h. around the track, sixteen hours daily, six days a week. The track’s structural layers are uniform around its length. Research focuses on surface failures, those in the top four inches of pavement. The inaugural research at the track tested 46 surface pavements developed by nine state transportation departments and the federal government. Each paid a fee for two years’ testing of two 200-foot sections of track paved with mix designs it devised, and each shared results on a Web site featuring field and laboratory findings. Coordinating placement of the unique track sections was a monumental task, complicated by variation in states’ lift expectations.
Since rugged terrain surrounds the test track, the contractors’ first step, in September 1998, was excavating 550,000 cubic feet of rock and dirt. The track’s length was stretched east-to-west to curtail shadows that change pavement temperature. At some points, 45 feet of fill was added.
The track base, 23 inches deep in all, uses improved subgrade soil topped with crushed granite and permeable asphalt-treated stone. This supports nine-inch and six-inch layers of two durable asphalt mixes. Reflecting an industry trend, the track exemplifies perpetual pavement, where worn surface layers can be milled off and quickly replaced. Its deep structure will endure for years.
Meeting specifications for 46 test surfaces required an unorthodox approach. Pavers advanced only 200 feet before changing mixes, precluding the usual mix adjustments made while paving, so these were made beforehand despite the resulting liberal use of mix. Sensors at several levels in the pavements monitor moisture and temperature, sending data to NCAT computers hourly. NCAT researchers regularly gather other data, such as friction and smoothness, location of cracks, depth of ruts, and mat density. Core sampling is also performed.
Volkert & Associates designed both the track roadway and the architecture of the research quarters. Montgomery, Alabama-based W. S. Newell undertook the first phase of construction: site preparation including the subgrade. A second phase, completing the track through the experimental mix layer, was handled by APAC–Couch Construction Division of Dothan. W. W. Dyar of Hamilton, Alabama, built the 4700-square-foot laboratory. Alabama’s DOT assumed most construction costs of the test track, in return for test sections. The university also acquired the land where the NCAT Pavement Test Track now resides, a proud achievement uniting several forms of engineering in skillful service to an industry, a government, and a people.