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Happy landings

Recycling has saved thousands of lorry journeys during construction of an airport apron, as Lisa Russell discovers.

You could reasonably expect construction of a major new airport runway to generate a good deal of road traffic. But work on a new apron and main runway upgrade at London Ashford (Lydd) Airport in Kent has avoided this.

Some 35,000t of deliveries have been kept off local roads, thanks to a determined effort to reuse as much material as possible, including breaking up the redundant second runway for use as aggregate.

Main contractor Foster Yeoman Contracting (FYC) has made extensive use of recycling and insitu ground stabilisation.

Project manager Colin Timmins estimates that some 60 lorry deliveries a day have been saved.

FYC's £3M contract includes construction of 24,000m 2of new apron as well as work to bring the main runway up to scratch for increasing volumes of UK internal and European air traffic.

The upgrades will prepare it for international Boeing 737 flights.

The overall surfacing operation will consume 1,400t of bitumen and involve laying 30,000t of asphalt across the rejuvenated runway and new apron. FYC made it a priority to adopt a sustainable approach throughout the project.

Recycling can bring substantial cost savings as well as cutting lorry movements. But there are other benefits. 'The wonderful thing about recycling is that you are your own master, ' says Timmins. With material readily available on site, there is no risk of delay caused by deliveries being held up.

Although parent company Foster Yeoman's prime business is in quarrying, 'we always look to recycle as much as possible', claims business development manager Nick Humby. 'The value of the quarry side of the business is in the stone that's in the ground.

The faster we use up that reserve, the shorter the life of the business for generations to come.'

The 24,000m 2apron is largely located on greenfield land, but two techniques have been adopted to minimise environmental impact: To keep volumes of imported materials as low as possible, the site is being stabilised using lime and cement.

Soil stabilisation subcontractor O'Keefe Soil Remediation has already placed two 250mm thick layers of stabilised sub-base material with a CBR strength of 30%. This involved removing the top 250mm of soil - a fine sandy clay with a little gravel - to formation level. Lime was then mixed insitu into the ground to a depth of 250mm, followed by stabilisation with Portland cement to increase bearing capacity.

The excavated soil layer was then replaced and similarly stabilised.

Breaking up the redundant second runway provided the raw material for a 200mm cementbound base on which the apron's asphalt top layers are laid. This required specialised equipment, starting with a Goliath mobile crusher to break up 6,000m 3ofthe old runway. A mobile recycling plant owned and operated by FM Conway produced the final material.

Design consultant Parsons Brinckerhoff specified Marshall asphalt for the binder and surface layers. This is a very high stability, stiff, dense graded mixture.

The apron is being surfaced with a 60mm binder course topped by a 40mm surface course. 'It is a very flat area and we are not inducing high falls, so the tolerances we are working to in laying the material are very tight, ' says Timmins.

The apron area is being profiled to ensure efficient runoff of surface water into newly installed, large capacity Gatic slot drains which will feed into an outfall basin. Reed beds will clean up the water before discharge.

The main runway was in poor shape but did not need full depth reconstruction. Cracks are being repaired before applying a regulating layer to achieve the correct profile. It will then be topped with Marshall asphalt binder and surface courses.

Ashford airport continues to operate as work advances. A phased approach has enabled FYC to close off outer 500m sections while keeping the airport's central 1km of runway open. However, it is now time to tackle the central section and night possessions have just begun.

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