Barrett Byrd Associates

A durable asphalt surfacing custom designed for use on Brands Hatch has been specified at a unique motorcycle track in East Anglia. Mike Walter reports

Growing popularity of a form of motorcycling known as SuperMoto has led to construction of the UK’s first purpose built racetrack for enthusiasts of the sport and for karting racers in Suffolk. The new racetrack – at the Wildtracks off road activity centre – features a 700m circuit, surfaced with a durable thin layer first used at legendary motor racing venue Brands Hatch.

The surfacing is based on Tarmac’s proprietary Masterpave asphalt material and was developed for motor racing use in association with materials specialist Nynas Bitumen. The new material has been coined the ‘Masterpave Brands Hatch mix’.

Design of a surfacing for a racetrack as opposed to a highway represents a totally different form of asphalt engineering. A racetrack has much lower traffic volumes than a road, but endures considerably higher stresses as drivers turn quickly and corner at speed more often. The new SuperMoto racetrack in Suffolk features a series of very tight bends and riders can reach speeds of up to 100km/h.

One significant advance made with the new material is its use of 6mm size high PSV aggregate, as opposed to 10 or 14mm size aggregate used in a standard Masterpave product. Tarmac Southern’s Anglia technical manager Greg Wood explains: “Use of smaller size aggregate produces a more compact asphalt mix with fewer air voids. This results in a greater surface area for a wheel to make contact with and better grip, which competitive motorsport demands.”

Standard Masterpave surfacing contains a high aggregate content, filler, cellulose fibre and a conventional binder grade to give the asphalt a high degree of stiffness. But the ‘Brands Hatch’ mix includes a polymer modified, high resistance binder developed by Nynas Bitumen known as Nypol HR. Use of this particular binder in place of a more conventional straight run bitumen gives the surfacing greater flexibility and added strength.

“Thin surfacings can be either stiff or flexible in nature, but the Masterpave Brands Hatch mix has been designed to be both stiff and flexible to suit the rigours of motor racing use,” adds Wood.

The sport of SuperMoto combines both on and off road racing. Motorcyclists competing at the new racetrack leave the 700m asphalt circuit and ride on a rough, unmade surface, 200m long which includes two earth mounds over which they jump. Competitors then rejoin the asphalt circuit and immediately turn through 180 degrees.

Mud and grit is easily transferred onto the track, but the abrasive action of gravel detritus does not affect the condition of the surfacing. This is due to the durable nature of the asphalt and its binder.

Nynas Bitumen’s southern area sales manager Miles Williamson says: “The action of grinding dirt into the track puts the bitumen binder under immense stress. Our polymer modified Nypol HR binder has, therefore, to be particularly strong to cope.”

Over 500 tonnes of the Masterpave Brands Hatch mix were produced for the Suffolk racetrack at Tarmac’s nearby Cavenham asphalt coating plant. Insulated vehicles delivered fresh quantities of the material to site and the surfacing was laid in two days by Tarmac South East Contracting with two paving machines working side by side. Laying of the material was carried out under the close supervision of contracts manager John Pelton.

A sub base of crushed concrete was overlaid with a 70mm deep binder course before the Masterpave surfacing was laid to a depth of 30mm. Great care was taken to ensure that the asphalt dispatched from each paving machine was knitted together to give a continuous and even distribution of surfacing.

The asphalt was rolled as soon as it went down to ensure compaction was completed before the material cooled. “The most important aspects to consider when dealing with thin surfacings are the laying and compaction,” says Greg Wood.

“The performance of the material is assessed at Tarmac’s Ettingshall laboratory where it undergoes wheel tracking, rutting and water sensitivity tests. The components of the material are also tested at the asphalt coating plant’s materials laboratory for quality control purposes.

“We increasingly supply asphalt to meet high performance end uses and the Masterpave Brands Hatch mix is a good case in point, designed as it is to suit high stress conditions,” he adds.

The material meets Clause 942 of the Specification for Highway Works for thin surfacings and has been approved for use under the Highway Authorities Product Approval Scheme.

BOX ONE:
High performance asphalt surfacing Masterpave was first specified for use on a motor racing site as part of repair works at Brands Hatch in Kent five years ago.

The track had been resurfaced with an asphalt that uses a high PSV stone but with conventional straight run bitumen. This proved a good material for all but the Graham Hill Bend.

This area of the circuit features a turn rising up after a steep drop where vehicles reach very high speeds and high G-forces press them down hard against the track. Difficulty with the Graham Hill Bend led to it being resurfaced on more than one occasion.

Tarmac’s solution was the development of Masterpave containing Nynas Bitumen’s high resistance binder Nypol HR. Early in 2003, Tarmac supplied this product for an extensive resurfacing contract at Brands Hatch. The ‘Brands Hatch mix’ has more recently been used to surface a Land Rover test track in Warwickshire and a karting circuit in Somerset.

BOX TWO:
The sport of SuperMoto is one of the fastest growing forms of motor racing in the country. Although still in its infancy in the UK, it has an established cult following. Several digital television channels screen competitive races from around the world and Channel 4 has begun to televise the event.

SuperMoto bikes are equipped with road going tyres and are powered with engines of up to 650cc. Construction of the SuperMoto race track at the Wildtracks off road activity centre in Suffolk allows local riders to compete and practice on a track specifically designed for the sport.

“This is the only major designated track for SuperMoto and for karting in the UK,” says Wildtracks owner and developer John Gorst. “Already the track is proving very popular with many riders from beginners to the top names in the sport.”

The first month of practice sessions at the new track over the winter attracted a turnout of over 60 SuperMoto riders and two rounds of the British Championships are scheduled to be held at the track in 2004.

Gorst adds: “The track will also be used extensively for karting and the National Karting Association’s Keith Barton has described the circuit as ‘brilliant and one of the best in the country’.”

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