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Test Drive

It will be years before we know whether Superpave lives up to its name, but encouraging reports are already rolling in. In New York, contractors repaved 50 kilometers of Interstate 81 across Cortland County with two-thirds original recipe and one-third Superpave. After just one winter, according to state director of technical services Paul Mack, the old-fashioned asphalt began deteriorating. “The Superpave section looks very good in comparison,” he says.

Superpave has seen its share of technical failures and real-world resistance. Several of the asphalt tests bombed in the real world, and Amoco’s Swanson says others are proving tricky to use. Although her technicians make careful measurements, she regularly haggles over the results with the hot mix plants. These firms, which supply construction crews with raw pavement, repeat the performance tests, often with different outcomes.

Road crews also face a learning curve. The new mixtures feature larger stones and are proving tough to compact, says New York State materials engineer William Brudi. In typical road work, a paving machine crew throws down a swath of piping-hot mix and gliding steel-wheeled rollers follow about 60 meters behind, ironing it down at temperatures near 93 C. But Brudi says that’s not hot enough for Superpave. Now, on a $90 million project to construct a 9-km HOV lane on the Long Island Expressway, rollers follow hot on the tail of the paving crew, compacting the mix at a blistering 150 C. “That demands a lot more coordination of the machines,” says Brudi. “The teams aren’t used to communicating, now they have to to get it right.”

Sometimes those who resist the newfangled technology have a point. At a 1993 job near Kingman, Ariz., contractors following Superpave guidelines omitted the antistripping chemical that is conventionally used to protect the road from moisture. Today, moisture cracks snake over the road’s surface. “Our feeling is that for us to blindly accept this design procedure without using our engineering knowledge is a disservice to the citizens of Arizona,” says state DOT engineer Julie Nodes.

The reaction of folks like Nodes is critical-Superpave’s fate rides on a thumbs-up from such officials because state DOTs finance the majority of the nation’s road construction. So far, most have taken up the voluntary Superpave specifications eagerly, with Indiana, Maryland and New York leading the way. Overall, 38 states now ask contractors to use the new performance graded asphalts, and nearly half are implementing the aggregate mix design.

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