| Growing enthusiasm for a form of motorcycling known as SuperMoto has led to the construction of the first racetrack of its kind in the UK, at the Wildtracks off-road activity centre in Suffolk, UK. The racetrack features a 700 metre circuit that has been surfaced with a robust thin asphalt material first used at the world famous Brands Hatch motor racing venue in Kent, UK. Masterpave Brands Hatch Mix Asphalt The surface in question is based on Tarmac's Masterpave asphalt material, and was developed by Tarmac Southern and materials specialist Nynas Bitumen for use on racetracks. The new material is known as the Masterpave Brands Hatch mix, and was laid at the Suffolk racetrack during October 2003. The Brands Hatch mix has more recently been used to surface a Land Rover test track in Warwickshire and a karting circuit in Somerset. Differences Between Highways and Racetracks Designing a surfacing material for a racetrack as opposed to a highway represents a 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 Use of Finer Aggregate and Its Effects One significant advance made with the new material is its use of 6mm size high PSV aggregate, as opposed to 10mm 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.’ Binders 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. Stiffness and Flexibility ‘Thin surfaces 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. SuperMoto Racing The sport of SuperMoto combines both on and off road racing. Motorcyclists competing at the new racetrack leave the 700 metre asphalt circuit and ride on a rough, unmade surface, which is 200 metres long and includes two earth mounds over which the riders jump. Competitors then rejoin the asphalt circuit and immediately turn through 180 degrees. The Effect of Gravel on Asphalt Surface 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. ‘The action of grinding dirt into the track puts the bitumen binder under immense stress. Therefore, our polymer modified Nypol HR binder has to be particularly strong to cope,’ says Nynas Bitumen’s Southern Area Sales Manager Miles Williarnson. Installation of the Asphalt Surface More than 500 tonnes of the Masterpave Brands Hatch mix were produced for the Suffolk racetrack at Tarmac Southern’s nearby Cavenham asphalt coating plant. Insulated vehicles delivered fresh quantities of the material to the site and the surface 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. Structure of the Racetrack Surface 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 surface distribution. Laying and Compaction 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 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.’ Summary 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. ‘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,’ concludes Wood. |