The science behind Miami GP’s “innovative” F1 track surface

Miami's new Formula 1 circuit has an "innovative" surface ahead of its inaugural grand prix on 8 May, mixing local limerock and granite to yield the expected grip and wear.

UK firm Apex Circuit Design has designed the 3.36-mile anticlockwise circuit – which winds around the Hard Rock Stadium in Miami Gardens – with an expected lap time of 1m35s and an average speed of just under 135mph.

Paving the track required 24,000 tons of asphalt, which was laid out over 85,000 yards in echelon over three lanes for an average track of 50-feet width. Construction scheduling had to be choreographed around the stadium’s multiple other events including the end of the NFL football season, a jazz music festival and the Miami Open tennis tournament.

“Of course, a lot of engineering and analysis has gone into the asphalt itself,” said Apex’s project director Sam Worthy. “The FIA requires the asphalt to be down at least 60 days ahead of the race weekend. We hit that, so it’s going to be well cured before the race happens.

“We’re starting to see the limerock aggregate peek through right now because we’re getting that top layer of binder coming off now. You can see white specks in it.

“Normally, limerock is a poor aggregate to use for F1 tracks: one, it is ‘friable’ and can chip and, two, it polishes. So you don’t usually get good tyre degradation and grip is reduced. But, in Southern Florida, the predominant aggregate is a more abrasive limerock.

“Our asphalt specialists, R3, looked into the local aggregate and they said they’d seen nothing like it throughout the world, as it is much harder than expected and will result – with the mix of 60% US-mined granite from Georgia – in suitable abrasiveness in our asphalt mix. R3 has been involved with most recent F1 tracks in some way, so their exposure to data from other venues gives us a good reference.

“What R3 found in South Florida is that ‘our’ limerock is unique because it has a very high silica content. Its texture is like little shards of glass, so as the limerock itself breaks down and degrades it exposes more of this silica and so you get an effect where it maintains a much higher tyre degradation than you’d usually get in with limerock elsewhere in the world.

“Granite was brought by train from Georgia, and so our mix is an innovative combination of granite and limerock that is all locally sourced – it’s nowhere near what people thought we’d have originally. We are very pleased with the results we’ve got.”

Super-flat track surface

Worthy also explained how the track’s super-flat surface was achieved despite a paucity of expertise in the local area when it came to the quality of finish that Apex was demanding.

“The entire team is very proud of what we’ve achieved in terms of track flatness,” he said. “A lot of hard work was put into that, because while local contractors were very good at what they do with their methodology, their technology was lacking – we had concerns with that. When we mentioned what the FIA specs were for laying asphalt, they said ‘it’s impossible to get it that smooth’. It scared the bejesus out of them!

“That’s when we had to find contractors who had the technology we are familiar with in Europe and elsewhere in the world and who were confident to supply us with what we needed. We relied on specialist contractors to lay the asphalt itself, although the base rock layer and subgrade and first two structural lifts of the asphalt, the second of which was ‘overbuilt’, was by local contractors. On completion of those first base layers we LIDAR-scanned the entire track, in order to generate a full 3D mesh of that surface prior to milling and final paving.”

Key to completing the process was enlisting the expertise of construction contractors, who ensured the track’s base layers were as smooth as possible.

“We worked with Rifenburg Construction from upstate New York, who are a recognised user and specialist in the use of Topcon electronic control of milling and paving,” added Worthy. “They used GPS-controlled micro-milling to bring the overbuilt second layer of asphalt to our design standards by taking our design data and  into their machinery. These micromilling machines use much smaller teeth in their milling process than you’d normally see to assure accuracy  to within millimetres.

“We milled a super-accurate surface that itself was very close to being race-ready, so that when they commenced the final top lift [of asphalt], which is an inch and a half thick, Rifenburg could focus solely on making it smooth and flat as they’re laying it. So they didn’t have to worry about anything else like the cross slope or the trench drain, because these criteria were already at the perfect elevation required.

“We paved the final surface course in ‘echelon’ [with three pavers running simultaneously to ensure hot seams between lanes to ensure a long life for the asphalt], the number of quality assurance and control personnel involved, following behind each paver, was really impressive. The paver would go by, with a truck dumping asphalt into a transfer vehicle, which had a driver with two spotters, and the paver would have a crew of six to eight people. Then behind the paver you’d have a sizeable team of quality people with three straight edges checking every direction as they’re rolling.

“The sheer number of people and effort that went into this final track laying process was immense. It was important to ensure no bumps between the paver lanes or at the seams, they did such a good job, which all folks who have since seen have commented upon really positively.”

One last step of the process

Worthy explained that there is a final stage of preparation required to make the entire track race-ready for the F1 weekend: “We have one remaining task with respect to the asphalt surface prior to the race, working with Roadgrip from the UK; we’ll be texturising the surface with their patented TrackJet equipment to uniformly strip the surface bitumen and to open the surface to the target macrotexture required by F1.

“This work will be an annual exercise; for Year 1 it is more aggressive as we are preparing the asphalt for its first race. In future years it will require track cleaning as much as is the case for the Singapore F1 venue, as the site is used for multiple other events between races and there is likely to be dirt and contamination to remove each year.”

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