Barrett Byrd Associates

Recent advances in materials engineering has led Exeter Airport to specify a durable new asphalt surfacing to renew part of its runway, writes Mike Walter

A fully laden Airbus A310 passenger aircraft can weigh as much as 123t and exerts considerable forces onto an airport runway when the wheels of the plane touch down. Airport authorities take no chances over the quality of surfacing specified on an airfield and a few airports such as Exeter are keen to try out the latest, most durable asphalt materials available when resurfacing is called for.

One recently developed asphalt surfacing material is known as Super AirMat and the material was laid for the first time on a runway in the UK by Bardon Contracting this October on a large part of Exeter airport. The material contains a durable variety of aggregate and a special polymer modified bitumen binder and has been designed by the materials specialist Bardon Aggregates in association with Nynas Bitumen.

Super AirMat contains a 10mm nominally sized gritstone from Bardon Aggregates in south Wales which has a very high polished stone value. This provides the surfacing with an exemplary level of grip which is demanded by airport authorities of material used to resurface runways. The aggregate is coated with Nynas Bitumen’s durable binder known as Nypol TS, which is designed to give good adhesion and cohesion with the stone. Added durability is afforded to the asphalt mix with the addition of cellulose fibres.

Resurfacing a runway using Super AirMat helps airport authorities to prolong the life of their asset and ensures the highest standards of safety for aircraft, says Bardon Aggregates’ regional technical manager, Chris Mellor.

“Super AirMat has been designed especially for use on airfields and is a very durable asphalt material which holds the aggregate firmly in place,” he says. “Laying the asphalt is a one-pass process. Two pavers work in eschelon to minimise the number of longitudinal joints in the material and once laid, the material does not have to be grooved as with the alternative Marshall Asphalt.”

The Nypol TS binder used to coat the aggregate is a polymer modified grade of bitumen. Properties contained within the binder cause it to become thixotropic when not under sheer loading, which helps to prevent it from draining from the stone when asphalt is being delivered to site. When mechanical action is applied – during paving and compaction – the binder becomes less viscous to make the asphalt more workable.

Nynas Bitumen’s product application manager for performance asphalts Jukka Laitinen says: “Asphalt material containing the Nypol TS binder can be compacted quickly, which helps surfacing crews who are working within a restricted timescale. The contractor at Exeter Airport faced stiff financial penalties if the runway resurfacing had overrun. We made up to four deliveries of bitumen each night to a nearby asphalt production facility to help ensure that enough asphalt material would be delivered to site in time.”

Bitumen and aggregate were mixed together for the Exeter Airport contract at two dedicated asphalt production plants belonging to Bardon Aggregates at Westleigh quarry close to the nearby village of Burlescombe. A total of 1500t of asphalt was supplied to site during two weekend overnight closures of the runway.

Resurfacing at Exeter was carried out by Bardon Contracting on a 660m long section of the runway which measured 20m across. Works were carried out following a successful trial of the material on a part of a disused runway at the airport. Runway resurfacing began with the planing out of 50mm of existing Marshall Asphalt surfacing, which was taken away to a tip on site for later reuse as a low grade material. A polymer modified bitumen bond coat was applied onto the base before the new Super AirMat surfacing was laid to a depth of 50mm.

Bardon Contracting’s operations manager John Rae said: “The team on site aimed to complete resurfacing works at 4am each Sunday morning to allow for the new material to cool. The runway was then swept carefully and line markings reinstated ahead of aircraft being allowed to use the runway two hours later.”

Exeter is one of the UK’s fastest growing regional airports. Passenger numbers increased three fold in the past few years and the airport's first one million passenger year should be reached in 2005/06. Work to extend the front of the main terminal building was completed this autumn to accommodate additional passengers and construction is due to start this winter on a new outbound baggage handling bay, additional aircraft stands and improvements to the airport’s fuel storage facility.

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