In summer 2012 the emphasis was on high-performance asphalt mixes and placement as crews of Austin Industries — under terrific deadline pressure — laid three courses of critical pavement at the new Circuit of The Americas (COTA) Formula 1 track just southeast of Austin, TX.
Executed in the midst of crews working to erect administration buildings, grandstands, an amphitheater, an observation tower, fences and landscaping, the paving at COTA took a little over four months. Each lift of asphalt was specifically designed to meet the standards of the sanctioning body, the FIA or Fédération Internationale de l’Automobile, and the rigors of the central Texas climate. Specifications demanded that the two top courses be placed in echelon, that is, by multiple pavers at the same time, to eliminate cold joints.
Compaction at the paver was required in advance of the rolling train. For this critical, high-visibility application Austin selected four Super 2100-2 asphalt pavers from Vgele with AB 600-2 TP2 screeds, and a host of Hamm vibratory and pneumatic compactors, including HD+ 90 VV-S rollers with split drums, and the new GRW 280 rubber-tired rollers.
The base course was designed to support the vertical forces of the cars. The binder or intermediate course was designed to support the horizontal forces of the cars during acceleration and breaking, and the wearing course was designed to provide grip at high speeds.
“The overall design of the asphalt mix for the track is crucial to the performance of the car,” said Oscar Rodriguez, Rodriguez Engineering, one of the subcontractors working on the project. ”We worked with Tilke Engineers & Architects, and our asphalt expert, Dr. Rainer Hart, to produce a mix that met their specifications.”
Ground was broken in January 2011. Circuit of The Americas sits on nearly 1,000 acres; 350 of which are the track itself. When construction was completed, COTA will represent a private investment of approximately $400 million.
The 3.4-mile track features 20 turns – some extremely sharp – plus inclines and a straightaway. Width varies from 32 to 52.5 feet and it’s designed to accommodate speeds approaching 200 mph. The maximum change in elevation is nearly 133 ft.
In mid-October 2012, in advance of the first race the weekend of Nov. 16-18, crews were putting the finishing touches on the track, with fresh coats of bright red paint to the edges of the margin. The track’s run-off areas will feature red white and blue stripes to commemorate the American heritage of the circuit.
But all this was possible due to the hard work of Austin crews using high-performance asphalt construction equipment to place bituminous lifts to exacting specifications, under blazing-hot environmental conditions that pushed or exceeded 100° F week after week.
Strict smoothness specs
The combination of strict smoothness specs, a tight schedule, rigorous mix designs, and having to work in the public eye meant a challenging project that would tax the best contractors.
By race day, approximately 700,000 cu. yd. of material will have been used to precisely construct the 3.4-mile track alone. During construction of the entire project, some 3.25 million cu. yd. of earth were moved, enough to fill a 1/3-mile-deep hole the size of a football field.
For the track, the project crew excavated approximately 10 ft. of Texas clay the entire length of the track. A black 30 mil polyethylene liner was then placed along the length of the grade as a separation layer. Then, 7 ft. of sandy, clayey loam select fill, 1.5 ft. of pit-run clayey sand, and 6 in. of crushed recycled concrete aggregate (RCA) was placed with conventional equipment.
This was followed by 6 in. of crushed limestone flex base and 3.1 in. of HMA base course, these layers placed by a single Super 2100-2 paver. The subsequent 2-in. binder course and 1.6-in. wearing course were placed by multiple Super 2100-2 pavers in echelon, resulting in a total asphalt pavement depth of 6.7 in.
A total of approximately 80,000 tons of HMA was placed on the track. Approximately 10,500 tons of surface mix were placed on the wearing course alone. When the paved run-offs and verges are included, a total of 21,000 tons of critical wearing course were placed.
“This is the only purpose-built Formula 1 race track in the United States, and it’s the first one we’ve ever been part of,” said Tom Byrum, management team member for Austin. “The section is 10-ft. thick, and was placed on a short schedule. Everyone in the world has his eyes on this track. So we have to be on top of our game, because when November comes, the whole world of racing will be watching.”
Getting 60 people, 40 trucks, a hot mix plant, four paving machines, and six to 10 rollers to all move in concert, with everyone on the same page, marching to the same beat, knowing exactly where to be every minute, was a daunting task, he said.
“There are many differences between building a Formula 1 track and a high-level interstate-type highway,” Byrum said. “No. 1, the surface mixture, as specified by Tilke, is a high-performance friction course with a high level of skid resistance, and asphalt cement is present at 6.5 percent of the mix. At PG 82-22, the liquid asphalt was highly modified with SBS polymer. It could be considered a Superpave mix, very similar to a stone matrix asphalt, with high binder content and gap-graded aggregate, providing rock-on-rock contact with minimal fines. It must be durable and skid-resistant.”
The smoothness spec was the toughest aspect of the job, he added. “More than anything, the flatness spec is what made this a huge challenge,” Byrum said. “The surface course has a very tight specification for smoothness, 2 mm over 4 meters [0.08 in. over 13 ft.].”
Meeting those specs on the top layer meant each lift below also had to be super-smooth. The 3.1-in.-deep base course has a PG 64-22 binder with a smoothness spec of 4 mm over 4 meters (0.18 in. over 13 ft.), while the 2-in.-deep intermediate “binder” lift in the middle has PG 76-22 liquid asphalt, with a little SBS modifier in it, and a smoothness spec of 3 mm over 4 meters (0.11 in. over 13 ft.).
While the base course was placed by a single paver, the binder and wearing courses were placed by pavers in echelon. “We had a V-shaped paving operation, with two pavers on the outside, trailed by a third paver in the middle,” Byrum said. “This had to be a continuous process and we could not stop throughout the pass. The transverse joints were placed at intervals where cars will be driving slowest, and the longitudinal joints are virtually nonexistent due to the echelon formation. A fourth paver was used in echelon with the other three where ramps widened the paving width for verges and run-offs.”
Flat and elongated particles were suppressed in these mixes, Byrum said. “During the crushing it’s always optimum to obtain cube-shaped or rounded aggregates,” he said. “That being said we had to use aggregate that will crush into that shape. The aggregate is hard limestone-dolomite, with a sandstone from Marble Falls. All aggregates were sourced in central Texas.”
Equipment helps meet specs
The specifications required use of pavers with compaction, and the team selected Super 2100-2 pavers with AB 600-2 TP2 high compaction screeds from Vgele. Also on the project were five HD+ 120 VV HF rollers, used on the wearing course, four HD+ 90 VV-S compactors with split drums for easier compaction without tearing on curved sections, three GRW 280 pneumatic rollers, and one HD 14 VV Compact Line roller, all from Hamm.
The small HD 14 VV compact roller was used for rolling up against positive and negative curbs, and also had an edge-rolling attachment to place a beveled edge on the lifts. The HD+ 120 VV HF rollers were kept in reserve for use on the wearing course, when the roller configuration would change. Also, a Vogele Super 800 paver with AB 200 TV screed was employed to pave some narrow run-off areas bordering the main line.
A Wirtgen W 210 cold mill was used to correct pavement smoothness, remove obstructions and as a trimmer. “We used it for ‘smart’ repairs, very minute repairs to the surface that will allow us to meet specification,” Byrum said. “The W 210 was used to shave off infinitesimally thin layers to make the lift as smooth as it can be.
“We’ve had a lot of very positive experience with Wirtgen mills, Vgele pavers and Hamm rollers,” Byrum said. “We’ve had great success with the rollers, and I’m a huge fan of the millers. The Vogele pavers are well-designed and work well for us. When you look at what was specified, and the choice in machines, it was pretty much a slam-dunk for us.”
The specified split-drum rollers enabled the drum sections to turn at slightly different speeds on tight radii. “Because of the sharp corners that we had to pave and compact, the split-drum was ideal for making those tight turns,” Byrum said. “If you don’t use the split-drum, the mat will shove and push and cut on those sharp turns.”
Outside of the sharp turns on the binder course, the HD+ 90 VV-S split-drum compactors also served as breakdown rollers in back of the pavers for all three courses. “The split-drum worked fine on the rest of the track too,” he said.
The pneumatic rollers served as intermediate rollers. “They kneaded and fixed the surface of the mat,” Byrum said. “This mix was somewhat tender so we kneaded it using those rollers. But on the wearing course, the pneumatic rollers were not allowed, except at the very end of the rolling train, and that was a whole other challenge.”
The AB 600-2 TP2 screeds on the Super 2100-2 pavers have a leading-edge tamper bar, and two trailing-edge pressure bars. The pressure bars were used in conjunction with the tamper bar in placing the limestone flex base and base course, but not the binder and wearing courses.
“For the binder and wearing courses we used the tamper bar in front, but not the pressure bars in back,” Byrum said.
“When we didn’t use the pressure bars we got about 88 to 89 percent density,” he continues. “When we turned them on we got 91 to 92. But our consultant preferred that we not use the pressure bars as the aggregate might fracture. In response we rolled it a little bit more.”
Specification for the binder course breakdown rolling was 94 to 97 percent density, and the rollers were getting 96. In general, density specs for each lift were in that range, with the wearing course a little higher.
“Everyone involved with this project – Austin, Wirtgen America, our distributor Cooper Equipment – all have given 110 percent, partnering together, to make this project a success,” Byrum said. “Those guys – our equipment consultants – were here whenever we needed them to help us be successful, and we could not have done it without them.”
Thumbs up from FIA
“Everything that I’ve seen so far has been absolutely first class, and the progress that’s been made since the last time that I was here is amazing,” said Charlie Whiting, who directs racing, safety and technical matters for FIA.
“The guys have done an awesome job, it really is quite fantastic. It’s built to the highest quality, exactly as we expected, and I’ve got absolutely no complaints whatsoever.”
Whiting visited in mid-September, about two months before Formula 1 racing was to take place at the track. All Formula 1 circuits must be inspected and approved by Whiting before they can conduct Grand Prix racing, and the motorsports veteran spent approximately two hours touring the facility along with representatives of COTA, general contractor Austin, and German track architects Tilke GmbH.
Whiting approved the circuit for Grade 1 status, which is the highest distinction awarded to a motorsports venue. The passing grade cleared the way for the circuit to conduct Formula 1 racing this fall.