Project Profile: A Smooth Finish

Jan. 1, 2009
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In late 2007, Bruton Smith, chief executive officer of Speedway Motorsports Inc., had a vision to build a one-of-a-kind drag racing facility that would become the crown jewel of the National Hot Rod Association (NHRA) racing circuit. Less than one year later, zMAX Dragway @ Concord held its first event with the inaugural NHRA Nationals on September 11, 2008.

zMAX Dragway is adjacent to Lowe’s Motor Speedway in Concord, a suburb of Charlotte, NC. Speedway Motorsports, a publicly held corporation, owns and manages seven racing venues across the nation. zMAX is its fourth drag racing track and the first four-lane, all-concrete facility in the United States.

“zMAX is the only four-lane drag strip that the POWERade Series races at,” says Adrian Parker, director of communications for zMAX Dragway and Lowe’s Motor Speedway. “The surface is smooth and there are no transitions, which could lead to record-breaking times.”

Construction began in January 2008 with an aggressive schedule that was approximately two-thirds of the normal construction timeline. From the very beginning, the design of track changed significantly. The Dragway’s original design included the two racing lanes, grandstands, a pedestrian tunnel, and a 54,000-square-foot starting line tower, housing luxury suites and the press box. Changes included two additional racing lanes, additional grandstands, and a second tunnel. The only thing that didn’t change was the drop-dead completion date. The track had to be ready for drivers and racing fans by September 11.

“Even with all the design changes we’ve had along the way, we stayed right on schedule,” says Jeff Black, project manager for Speedway Motorsports. “Our facilities at zMAX are a step above with great amenities and a fan-friendly venue.”

The racing lanes are 4,000 feet long-the equivalent of 13 football fields. The first quarter mile is all concrete, and asphalt accounts for the remaining 2,600 feet. Granite Contracting won the bid for the asphalt paving of the racing lanes and the asphalt parking lots.

Granite Contracting is a turnkey site development company in Charlotte and has completed various projects at Lowe’s Motor Speedway for the past 10 years. President Steve Cosper knew from the beginning this would be the most demanding paving job his company had undertaken.

“Hands down, this was the most challenging paving project we’ve done,” says Cosper. “In the paving industry, the high watermark for tight tolerances are airports, and these specifications were even tighter.”

There is a good reason for such a tight tolerance. With racecars traveling at top speed down the drag strip lanes, there can be no differential where cars can possibly lose contact with the pavement. The paving structure called for 4.75 inches of hot mix asphalt with a one-eighth-inch tolerance. If that wasn’t difficult enough, the specifications mandated that the asphalt mat could not be touched with a lute or a shovel after it emerged from the screed.

“We couldn’t rake the surface or fill any dips,” Cosper says. “If there were any irregularities, it had to be milled back up and repaved.”

At the take-off, Cosper knew the mix design and tight specifications would require a larger highway-class asphalt paver. It was important to get a paver that could meet the one-eighth-inch tolerance with the precision needed to lay a perfectly smooth mat. Cosper contacted ASC Construction Equipment and inquired about the new Volvo pavers recently introduced to the marketplace.

Why would Granite risk using a new, completely redesigned asphalt paver with so much riding on a near-perfect paving operation? Add to that the fact that his employees had no previously experience with the new paver.

“We have used Blaw Knox pavers for years, and I was pleased that Volvo bought the line,” says Cosper. “It was a good time for us and for Volvo to demonstrate this new class of asphalt paver on an actual paving operation.”

Dave Reger, asphalt industry manager for Volvo Construction Equipment, brought in a new Volvo PF6110 tracked paver and Omni 318 vibratory power extendible screed for the job. According to Reger, the PF6110 has a redesigned undercarriage with a new tandem-bogie distribution system that provides optimal traction and allows the paver to balance itself. The tandem-bogie pivot allows the machine’s weight to shift smoothly during operation and maintain contact with the ground. The Omni 318 screed is electrically heated which enables a consistent flow of material.

“The PF6110 performed very well,” says Reger. “We recommended a tracked paver over a wheeled paver to maintain the required consistency in the paving operation. It was critical that the machine stayed level. Granite could not risk a chance of leaving marks in the asphalt race lanes, so it was critical to use a paver designed to meet this special need.”

Cosper agrees. “The pull-off was critical. Many times when a machine first pulls off, the screed will rise or fall. This paver and screed were very consistent in behavior, and it held the grade
very well.”

The paver also was equipped with TopCon’s grade-control system, which helped with the critical pull-off and with longitudinal consistency. Reger says he and the Granite crew worked closely with TopCon experts to ensure all systems were operational and in sync to assure a quality surface. Granite also built custom 6-foot rails for the screed to ensure a flawless pull-off.

The design specifications called for three lifts of asphalt on the track: a binder lift, a coarse-surface lift, and a finer-surface lift. The mix design was not the standard hot mix asphalt typically used in Superpave mixes for most highway paving projects. The mix used on the track was a more traditional Marshall mix.

“It’s a richer mix. The surface course has a higher percentage of liquid asphalt and a lower air-void content than normal. That gives the pavement more rubber on asphalt contact.”

Based on rideability tests, which are considered the best indicators of meeting tolerance specifications, Granite reached near perfection. Smoothness was determined by using a California Profilograph, and the final results dramatically exceeded project specifications. Vertical deviation in the pavement surface was only one-fourth of what is allowed by the tight requirements. A material transfer vehicle was used for the final lift, so there was no chance of a material truck bumping the paver and causing irregularities in the mat.

Cosper credits planning, training, and quality control to the success of this paving project.

“This project required tremendous attention to detail,” Cosper said. “There were so many things that could have gone wrong.”

For instance, Granite spent more time than typically necessary in fine-grading the subgrade and stone base prior to paving. Granite utilized a Volvo 720B motor grader equipped with a Trimble laser-guided grade control system from Spectra IS for the operation. The Trimble system utilized laser beams to guide the motor grader and ensure accuracy with an effective radius of 600 feet. This allowed a large area to be graded without resetting the system’s guidance system. Grades were constantly checked to insure that the finished stone grade was within one-quarter inch of plan elevation along the entire racing area.

Training was also an integral part of planning. Granite, ASC, and Reger spent a lot of time prior to starting the job providing refresher training for Granite’s crew.

“We repeatedly reviewed the basic fundamentals of asphalt placement, as well as the project specific challenges,” said Reger.

It was risky introducing a crew to new equipment; however, according to Reger, the crew found the Volvo PF6110 very operator friendly.

As the paving commenced, quality control was of the utmost importance. Cosper explained that crewmembers were assigned specifically to monitor different areas of the operation.

“One man’s job was to coordinate the flow of asphalt trucks in and out of the job site,” he said. “In addition to quality control at the plant, we also had someone constantly monitoring the mix as it was being placed to insure we had no material segregation. Another crewmember did nothing except monitor the compaction of the asphalt once it was placed. Then someone else was assigned specifically to monitor the grade control system to ensure elevation, smoothness, and
rideability.”

We looked at every aspect of quality assurance in our process, starting with the mix design to the asphalt production to the actual placement,” said Cosper. “We planned for everything we could possibly anticipate and focused on the smallest detail-and it paid off.”