Twenty-seven tracks host paid NASCAR Cup Series races in 2022. Only the Nashville Superspeedway was designed with a concrete running surface. Martinsville installed concrete in the curves in 1976, while Bristol and Dover switched from asphalt to concrete in 1992 and 1995 respectively.
The 1.33-mile Nashville runway is a D-shaped oval and the longest of the four concrete-containing runways. At 14 degrees incline, it is slightly more inclined than Martinsville (12 degrees), but much less inclined than Dover (24 degrees) or Bristol (24-28 degrees). If we count half of Martinsville, concrete represents 13% of the NASCAR Surfaces Cup Series. Dirt constitutes 3.7%, leaving the asphalt representing the remaining 83.3%.
Concrete vs asphalt
Concrete and asphalt are both composites: aggregates (also known as “small rocks”) bonded together by a glue-like material called a binder. The concrete dates back to the Roman Empire, while the first paved roads were not built until 1848. The nature of the collectors explains the difference in timelines.
Concrete usually uses a Portland cement binder, a mixture of limestone and clay. Asphalt uses bitumen, a black tarry substance derived from the heavier components of crude oil, as a binder. The binders determine the method of application. While the concrete is poured and hardened, the asphalt must be heated to a high temperature before extrusion and allowed to cool.
As asphalt is more flexible than concrete, asphalt can be laid in long, continuous swaths. The concrete must be poured in sections to avoid damage caused by expansion and contraction induced by atmospheric agents. The lines between the concrete sections also help with water drainage. This is necessary because concrete is less porous than asphalt.
The flexibility of the asphalt means that it does not distribute loads. Asphalt undergoes greater and more concentrated stresses than concrete. The following figure shows typical stress distributions (in red) for asphalt and concrete.
As you can imagine, from this graph or your personal experience with potholes, asphalt is more easily damaged than concrete. Asphalt simply cannot withstand the high forces of racing cars taking tight turns at high speed.
Transportation engineer Van Walling compiled the fascinating compendium (not yet published). Almanac of the oval track. The three volumes document 45 years of in-depth research on over 1,000 tracks in the United States and abroad.
Martinsville, Walling explained, turned to concrete because racing cars damaged the asphalt in the corners. Trucks can damage the asphalt in circuits off the freeway ramps in the same way.
“Between the high temperatures and the strength of the vehicles,” Walling said, “the asphalt can be moved, creating a texture like a washboard.”
While the “push,” as the phenomenon is called, is annoying for an exit ramp, those bumps create serious problems for racing cars. Track operators have no choice but to frequently refurbish or reconstruct the surface or switch to concrete.
This is not to say that the concrete tracks are waterproof. In 2004, Jeff Gordon lost a Martinsville race due to the concrete coming off the track. In 2018, a piece of Dover’s concrete surface loosened and damaged Jaime McMurray’s car. The debris from the impact broke the glass of a pedestrian crossing above the competition surface. That episode prompted Dale Earnhardt Jr. to tweet that “The asphalt is for racing. Concrete is for pavements “.
Walling, who studied the original plans for Daytona International Speedway, said NASCAR founder Bill France Sr. wouldn’t necessarily agree.
“He wanted the corners of Daytona to be concrete,” Walling said. “The problem was the cost.”
Concrete requires a much larger initial investment, and France was already struggling for funding.
“He originally designed a 60-foot running surface,” said Walling, “but in the end he was content with 40 feet.”
If France hadn’t found the money, Walling says, Daytona could have become a much flatter track. The initial cost is why nearly all new tracks are built with asphalt, even if maintenance is more expensive in the long run.
How the race actually changes
The main grip mechanism on any track is the deformation of the tire around the aggregate. Concrete, by its nature, is smoother than asphalt. When NASCAR measured the track surface roughness in 2019, Martinsville, Dover and Bristol were the three smoothest tracks.
The second gripping mechanism is the adhesive interaction between the rubber molecules on the track and the tire. Although Goodyear designs its tires to deposit rubber onto concrete tracks, the rubber does not sit still.
“At speed,” said Greg Stucker, Goodyear’s director of racing, “the track will progressively turn black as the cars lay the tire on the concrete surface and then turn white back under the warning flag as the tires pick up much of that rubber. . Keeping up with that transition is an important element of the race strategy ”.
A driver loses traction on a concrete track much faster than on asphalt. Drivers have already driven more in 2022 with the Next Gen car than in all of 2021. The accident rate is also on the rise.
The concrete surface of Nashville can be a real challenge. Dover, the only race of 2022 on an all-concrete track so far, has had 13 yellow cards. This is almost double the number of yellow cards in each of the previous two games and triple the number of each of the previous two.
On the plus side, concrete doesn’t wear out as fast as asphalt. Even if the car is new, the surface will not have changed much since last year. The tires are also familiar. The teams used the Nashville left tire three times (including Dover) and the right side six times this year. They also raced the same left-right setup twice: in Charlotte and the Texas All-Star Race.
Black and white
Keeping track of color is important.
The sun emits a spectrum of electromagnetic waves. The little band that we can see is what we call light. But the sun also provides infrared waves, like the heat lamps that restaurants use to keep food warm. Its ultraviolet waves are the reason why you should wear a lot of sunscreen on the track.
Different colored surfaces interact differently with the sun’s waves.
We see objects because they reflect, emit and / or transmit light. A red car absorbs all wavelengths of light except for those corresponding to red. Only the red wavelengths reach our eyes.
White surfaces reflect most of the wavelengths of light. That’s why you see concrete as white: white light is the sum of all the colors of light. Black surfaces, on the other hand, absorb a lot of light. Because no light is reflected, you see black. The same thing happens with infrared waves, which cause black surfaces to heat up faster than white surfaces.
The white traces also reflect more light into the drivers’ eyes. Pilots will need colored detachable visors for the local 4pm start (5pm east), which will be broadcast on NBC.
The heat causes the bitumen in the asphalt to release oils which make the track more slippery. This does not happen with concrete.
The end result is that a concrete track does not change over the course of a race as much as an asphalt track. The Nashville Superspeedway should be easier for team leaders to follow because changes in temperature will not change the competition surface much.
On the downside, if a team gets the setting wrong, the track is far less likely to come to them during the race.