“Nobody thinks about asphalt until it comes apart,” Bob Harrington says. “Then, everybody’s interested.”
Harrington is always thinking about asphalt. After building airport runways during the Vietnam War, he embarked on a career in conventional paving. When track owner Roger Penske called about a job at Michigan International Speedway in 1994—the two-mile oval needed a new surface—Harrington and his team came up with a formula to polymerize racing surfaces. It was the beginning of a long collaboration. Harrington has since worked on about thirty tracks, from Daytona to Laguna Seca.
“To build a track is very expensive,” Harrington says. “The racing surface is not an immediate revenue source. But you need it to get other revenue streams going, like beer and hot dogs. So much of motorsports is via TV viewership. The last thing you want is to have the track start coming apart.”
He explained to us what goes into paving a modern racetrack—and why it’s much more complex than paving the highway you use to commute to work.
A. Asphalt for racetracks contains a polymer called styrene-butadiene-styrene (SBS), similar to what makes up Styrofoam cups. This raises the asphalt’s melting point so that it can stand up to the summer sun and hot, supersticky racing tires. The asphalt must therefore be laid down at a higher temperature—about 320 degrees Fahrenheit versus 200 to 300 degrees for public highways. Because of this, it’s mixed as close as possible to the track and transported in insulated trailers. Sometimes, a portable factory setup is brought to the site to streamline the process.
B. A rubber-tired crane is fitted with a rear-mounted generator. A conveyor carries the mix uphill to the paver.
C. The edge of a strip of asphalt is less dense and thus lets in more water—that’s why seams between highway lanes often erode prematurely. To prevent this on a racetrack, the crew rips up and repaves the edges, ensuring that every part of the pavement has between 92 and 97 percent of its maximum theoretical specific gravity.
D. The track is laid down in three asphalt layers. The base layer is 2.0 inches thick. The middle layer is 1.5 inches thick, and the crew measures it with a profilograph to identify all the bumps and dips—only a certain number are acceptable per mile of pavement. Then they carefully lay down another 1.5-inch-thick wearing surface as the top layer.
E. Racetracks are designed to support huge lateral loads from race cars stopping, turning, and accelerating; that’s the opposite of highways, which are much thicker so they can support extreme vertical loads—like trucks weighing 50 tons.
F. Banked turns, like those at Talladega Superspeedway (repaved in 2006), present special challenges, as heavy construction equipment must be modified to work at severe angles. Bulldozers at the top of the banking, each with an arm, reach over the retaining wall. Cables pass through their arms, preventing the paver and the roller from sliding down the turn. Tension is constantly adjusted so that the roller and the paver stay flat—otherwise they’ll lay down uneven pavement.
In Case Of Emergency
For all the care taken in construction, racetracks still develop potholes. Fast-Track 500, shown here, is one type of emergency repair kit. It has the consistency of brownie mix but hardens in minutes (this example was poured into a cake pan). The compound is designed for hot, dry conditions—quite unlike the cold and wet weather that prevailed when a pothole infamously interrupted the 2010 Daytona 500 for more than two hours. The material that ended up working that day? Bondo.
“The asphalt in modern-day racetracks has nothing to do with state-highway work. A racetrack has no vertical loading to speak of,” Harrington says.