A road-building approach pioneered in the late 1980s and early 1990s that supposedly makes for more durable highways is slowly gaining converts, but some questions have been raised about whether it is being implemented to the full extent its developers intended.
Only seven states have fully embraced the technique known as Superpave (SUperior PERforming Asphalt PAVEments), which is more expensive than traditional asphalt highway construction. Some researchers tout the system, while others say the innovations may not be as good as they were touted to be.
At Washington State University in Pullman, WA, civil engineering professors Tom Papagiannakis and Eyad Masad are big believers in Superpave, which basically tailors the asphalt mix to the specific climate and traffic conditions. For instance, making sure the rocks in the mix are angular rather than round, and bound tightly with liquid asphalt, can help prevent the "shoving" that happens at intersections by the force of vehicles, especially trucks, stopping at traffic lights.
Papagiannakis and Masad consider Superpave the biggest advance in the field since the late 1940s, saying it put researchers on the right track to look at the scientific reasons behind pavement failures. The two professors head the Washington Center for Asphalt Technology, which opened earlier this year.
The center, supported in part by donations from the road construction industry and the state Department of Transportation, features $300,000 in equipment that allows the researchers to design asphalt mixes to meet Superpave specifications. A $40,000 compactor can simulate 10 years of road wear in 24 hours, and ovens test asphalt in temperatures ranging from minus 30 to 180 degrees.
In Washington, a fifth of the state's major road projects use Superpave methods, with plans to completely switch over by 2005.
On the other end of the country, the University of Central Florida in Orlando is one of five universities chosen by the state to teach the art of Superpave. The university's new Geotech and Pavement Lab will help determine the right mix to use in Florida's tricky conditions of high groundwater and sinkholes. Engineering students at UCV will learn Superpave techniques, while the state DOT will use the lab to train employees.
A local engineering firm is conducting Superpave testing for construction of the first Superpave project in central Florida, Highway 429, a 32-mile toll road west of Orlando.
While Washington and Florida are pushing ahead with Superpave, researchers at the University of Arkansas claim that questions remain about the durability of Superpave.
To fully implement Superpave specifications, a shear tester is supposed to be used to check a mixture's performance. But with a price tag of $250,000, the researchers say, few Superpave projects are using the tester.
Superpave-type mixtures are much more porous than traditional asphalt mixtures. When it is installed over existing asphalt, water often seeps through and puddles between the old and new layers, says civil engineering professor Kevin Hall. That can cause wet spots on the road surface and increased rutting in the new layers.
Hall and other Arkansas researchers have been developing a cheaper lab-based test for asphalt mixture durability.