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.