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Dr. Diandra: The concrete facts about Nashville Superspeedway

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In 2022, 27 tracks will host points-based NASCAR Cup Series races. Only the Nashville Super Speedway was designed with a concrete racing surface. Martinsville set concrete in corners in 1976, while Bristol as well as Dover switched from asphalt to concrete in 1992 and 1995 respectively.

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The 1.33-mile Nashville track is a D-shaped oval and is the longest of the four concrete tracks. At 14 degrees of bank, this is slightly more than Martinsville (12 degrees), but much less than Dover (24 degrees) or Bristol (24-28 degrees). If we count half of Martinsville, concrete accounts for 13% of NASCAR. Surfaces of the Cup series. Dirt makes up 3.7%, the remaining 83.3% is asphalt.

Concrete versus asphalt

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Concrete and asphalt are composites: aggregates (also known as “small stones”) bonded together with a glue-like material called a binder. Concrete dates back to the Roman Empire, and the first paved roads were only built in 1848. The nature of the binders explains the difference in time.

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For concrete, a Portland cement binder, a mixture of limestone and clay, is commonly used. Asphalt uses bitumen, a tarry black substance derived from the heaviest components of crude oil, as a binder. Binders determine the method of application. While the concrete is being poured and cured, the asphalt must be heated to a high temperature before being extruded and allowed to cool.

Because asphalt is more flexible than concrete, asphalt can be laid in long continuous strips. Concrete must be poured in sections to prevent damage from expansion and contraction caused by the weather. Lines between concrete sections also aid in water drainage. This is necessary because concrete is less porous than asphalt.

The flexibility of asphalt means that it does not distribute loads. Asphalt experiences larger, more concentrated stresses than concrete. The figure below shows typical stress distributions (highlighted in red) for asphalt and concrete.

Graphic showing how concrete and asphalt handle stress differently.  Concrete distributes stress, but asphalt does not.

As you can guess from this chart or from your personal experience with potholes, asphalt is more easily damaged than concrete. Asphalt simply does not withstand the high loads of racing cars that go through tight turns at high speed.

Concrete cost

Transportation engineer Van Walling compiled a fascinating (as yet unpublished) collection Oval Track Almanac. The three volumes document 45 years of extensive research on over 1,000 tracks in the United States and abroad.

Martinsville, Walling explained, was reduced to concrete because the race cars damaged the pavement on the corners. Likewise, trucks can damage asphalt on expressway exits.

“Due to the heat and the strength of the vehicles,” Walling said, “asphalt can be moved around, creating a texture similar to a washboard.”

Bye “pushing“What is the name of this phenomenon, annoying off-road traffic, these bumps create a real problem for racing cars. Track operators have no choice but to frequently replace or resurface or switch to concrete.

This does not mean that concrete paths are impenetrable. In 2004 Jeff Gordon lost race at Martinsville due to the removal of concrete from the road. In 2018 part of Dover loosened concrete surface and damaged Jaime McMurray’s car. Debris from the impact shattered windows in a pedestrian crossover over the racing surface. This episode prompted Dale Earnhardt Jr. to tweet that “Asphalt for racing. Concrete for sidewalks.

Walling, who has studied the original Daytona International Speedway blueprints, said NASCAR founder Bill France Sr. would not necessarily agree.

“He wanted the corners in Dayton to be concrete,” Walling said. “The problem was cost.”

Concrete requires a much larger initial investment, and France has already struggled for funding.

“He originally planned for a 60-foot race surface,” Walling said, “but ended up with 40 feet.”

If France hadn’t found the money, Walling says Daytona could have been a much flatter track. The upfront cost is why almost all new tracks are built with asphalt, even though they are more expensive to maintain in the long run.

How concrete is changing racing

The primary mechanism for traction on any race track is the deformation of the tire around the machine. Concrete is inherently smoother than asphalt. When NASCAR measured track surface roughness in 2019 Martinsville, Dover and Bristol were the three smoothest runs.

The second adhesion mechanism is the adhesive interaction between the rubber molecules on the track and tire. While Goodyear designs its tires to fit the rubber on concrete tracks, the rubber doesn’t stay in place.

“At speed,” said Greg Stucker, Goodyear race director, “the track fades to black as the cars lay down rubber on the concrete surface, and then turns back to white under the warning flag as the tires take away most of that rubber. Keeping up with this transition is an important element of racing strategy.”

The driver loses traction on a concrete track much faster than on asphalt. In 2022, with the Next Gen car, drivers have already cheated more than in the whole of 2021. The accident rate has also increased.

Nashville’s concrete pavement can be a real problem. Dover, the only 2022 race on an all-concrete track, received 13 warnings. This is almost twice as many warnings in each of the previous two races and three times as many in each of the previous two.

One of the positives is that concrete does not wear out as quickly as asphalt. Even though the car is new, the surface hasn’t changed much since last year. The tires are familiar too. Teams have used the left-hand tire in Nashville three times this year (including at Dover) and six times on the right. They even competed in the same left-right configuration twice: at Charlotte and at the All-Star Race in Texas.

Black and white

The color of the track matters.

The sun emits a spectrum of electromagnetic waves. The tiny streak that we can see is what we call light. But the sun also emits infrared waves, like heat lamps that restaurants use to keep food warm. It is because of its ultraviolet waves that you should wear a lot of sunscreen on the track.

Different colored surfaces interact differently with solar waves.

We see objects because they reflect, emit, and/or transmit light. The red car absorbs all wavelengths of light Besides corresponding to red. Only red wavelengths reach our eyes.

A graphic showing how white light (light of all colors) hits a red surface.  The surface absorbs all light except red.  This light is reflected in our eyes.

White surfaces reflect most wavelengths of light. That’s why you see concrete as white – white light is the sum of all the colors of light. On the other hand, black surfaces absorb a lot of light. Because the light is not reflected, you see black. The same thing happens with infrared waves, which cause black surfaces to heat up faster than white ones.

Graph comparing light falling on black and white surfaces.

White tracks also reflect more light into the eyes of drivers. Drivers will need tinted visors for the 4:00 pm local time (5:00 pm ET) launch, which will air on NBC.

The heat causes the bitumen in the asphalt to release oils that make the track more slippery. This does not happen with concrete.

The end result is that the concrete track does not change as much during the race as the asphalt track. It should be easier for crew leaders to keep an eye on the Nashville Superspeedway because temperature changes won’t change the racing surface as much.

On the other hand, if a team misses a set-up, there is a much less chance that the track will hit them during the race.


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