| Two redundant runways at Bristol International Airport are being brought back into use as taxiways and areas designated for light aircraft refuelling and parking. The former military airstrips were last used by aircraft in WWII and have been rejuvenated with a selection of asphalt surfacing materials, one of which is designed to resist fuel. Use of Fuel-Resistant Asphalt Use of the fuel-resisting asphalt at Bristol represents the first time the material has been specified on an airfield in this country. The material is based on a product known as Bardon 10mm Forpave and has been produced using a fuel resisting binder known as Nyguard. The Binder The binder is often used in asphalt designed to resurface motorway service areas and bus depots where fuel spillage is likely. Surfacing for the Bristol contract was carried out by Bardon Aggregates and the binder has been designed by materials specialist Nynas Bitumen. Durability and Deformation Resistance ‘We have specifically designed a material that not only resists fuel spillage damage, but is highly durable and provides excellent deformation resistance,’ says Bardon Aggregates’ regional technical manager Chris Mellor. Binders and Strength The binder’s ability to resist fuel lies in a special blend of polymer modified ingredients which also help give the asphalt added strength when it is put under pressure. Nynas Bitumen senior chemist Dr lan Lancaster explains. Stiffness ‘A high level of stiffness is afforded to asphalt containing Nyguard, which remains unaffected should fuel be spilled. The binder was first developed about five years ago and can withstand enormous point loads exerted on an airfield by aeroplane tyres,’ he says. Crushed Quartzite Aggregate The Nyguard binder specified for the airport surfacing was mixed with a durable crushed quartzite aggregate at Bardon’s Westleigh asphalt plant in Devon. A total of 240 tonnes (t) of the fuel-resisting asphalt was laid at Bristol to a depth of 30mm by Bardon Contracting. The material represented a fairly small, yet hugely significant part of a larger surfacing operation, which involved laying nearly 7,000t of asphalt. Airfield Surfacings The airport’s advisor, Bristol Engineering Consultancy, requested that three further types of surfacing material were specified for the airfield. The taxiways measure 500m and 300m in length respectively one was surfaced with Bardon 6mm Smatex, the other with Bardon 10mm Smatex. Both stone mastic asphalt materials were produced using standard 50 penetration binder. Part of the new southern apron not designated for aircraft refuelling was surfaced using a Bardon 10mm Smatex Industrial surfacing, again produced with a straight run bitumen. Surfacing took place largely during the day, with night works required to tie in to the runway. Repair and Reinstatement of Runways The two former runways, rejuvenated into taxiways, aprons and refuelling areas were used by fighter aircraft in WWII but fell into disrepair and have largely been unused ever since. Reinstatement and repair were carried out to much of the runways prior to them being resurfaced and extra carriageway strength was provided with use of a glass geomembrane rolled out beneath the binder course. Resurfacing Just a Part of the Airport Refurbishment Resurfacing of the former runways has been carried out as part of a larger scheme headed up by main contractor Nuttall, to develop airport facilities including a new aircraft hangar and offices for the Bristol Flying Club on the south side of the airport. The airport’s new light aircraft hangar stands at around 13m high with a clear opening span of 50m by 30m, and works on the hangar are soon to be completed. Resurfacing Process for the Runways ‘The old runways were of very thin construction and unusable. We filled potholes, carried out patch repairs and strengthening before overlaying the existing construction with a 20mm sealing layer,’ Nuttall site agent John Hutton says. Glassmat geomembrane was then placed, after which binder and various surface courses were laid. Reprofiling and Drainage of Runways Taxiways and aprons have been reprofiled to allow efficient run off of surface water into newly installed, large capacity Gatic slot drains which take water through the drainage system to new interceptors and soakaways constructed on the perimeter. Summary ‘Bristol International Airport is designated an environmental source protection zone by the Environment Agency and as such large interceptors, fuel stop chambers and soakaways have been incorporated into the scheme,’ Hutton added. |