Tarmac's John Lennon Airport resurfacing: Specialist focus: Quarrying & Aggregates

Runway resurfacing is a unique sector within the paving industry and one that is evolving. The boom in low-cost air travel is putting additional demands on contractors and materials suppliers, which are responding with new ideas - as at John Lennon airport.

Tarmac National Contracting has just finished its largest airfield job to date at Liverpool's regional airport, a £10m contract for resurfacing the runway, taxiways and apron for main contractor Amec. There have been 'firsts' throughout, including first use of innovative materials - for an airport - and unprecedented quantities of work in short shifts.

Both have resulted from pressures now typical for UK airports. Demand for runway availability at Liverpool, for Easyjet, Ryanair and others, meant only six hours were available for Tarmac's work each night. Laying a total of 90,000t of material then became a far more considerable challenge. Maximising asphalt production and laying within the hours available would be critical and led to selection and first use of foam mix recycled asphalt at an airport.

Value engineering

Tarmac undertook a value engineering exercise as part of six months of planning and pavement design prior to site work starting in September last year. The company's FoamMaster system, with Nynas Bitumen's Nyfoam bitumen binder, scored highly because it would use around 4,000t of planings, save import of the same quantity of virgin aggregate and therefore present some of the environmental benefits the airport operator was looking for.

The recycled asphalt could also be laid in one pass in 7.5m-wide strips along the whole 2.4km length of the runway's shoulders. "This allowed the shoulders to be used for construction traffic. Vehicles were run on the shoulders while we reconstructed the main runway across the remaining 45m width, shaving time off the programme," says Tarmac's project manager Andy Reynolds.

The use of FoamMaster at John Lennon represents a major advance for airfields surfacing showing the sector's clients are opening up to new ideas. The recycling process has been proven extensively on the UK's roads, but the airfields sector is traditionally more conservative in nature.

According to Tarmac National Contracting director Paul Fleetham, modern alternatives, which are generally quicker to lay than conventional Marshall Asphalt, were also considered for the main runway as part of the value engineering exercise. "We looked at competing products, but to be fair, Marshall Asphalt is tried and tested and clients are understandably cautious," Fleetham says.

Nonetheless, airport operators are keen to see better value and Tarmac was able to specify a very strong pavement for the runway, consisting of a 100mm layer of dense macadam base course, a 60mm Marshall Asphalt binder course and a 50mm Marshall surface. Each layer was bonded together and fixed to the runway's concrete base with Nynas Bitumen's Nyclean bond coat - effectively creating a single pavement layer.

Bonding the upper layers is normal practice, but creating a strong bond with a concrete base is an advance of bondcoat technology, which has also been exported from highway to runway surfacing. "I've not seen anything like it. When we went in to get cores during trials of the pavement, it was stuck solid," says Andy Reynolds.

"Nyclean is a 'non pick-up' material," says Nynas Bitumen's product applications manager Dennis Day. "It is a bitumen emulsion that breaks very quickly without pick-up by site traffic thus enabling contractors to maximise available time under the working window constraints of most airport contracts. Nyclean only melts to create a strong bond when hot asphalt is laid on it, saving a lot of time and difficulty associated with clean-up operations."

Despite its best-value engineering efforts, Tarmac still needed around six months to complete its work, partly because it had to be done in the airport's quiet season. Bad weather stopped work on 22 nights. During the rest, Tarmac had six planers taking off the old asphalt and two mobile asphalt plants on site producing the new material. Four paving machines worked in echelon across the runway supplied by a50-strong fleet of 20t wagons shuttling between planers, plants and pavers.

"It is an issue of logistics, ensuring sufficient asphalt can be mixed and supplied as quickly as the old is planed off. The quantities have to be balanced," Fleetham says. "The volumes at John Lennon are the largest we have produced and laid in single shifts. There was a lot to do each night in a very limited six-hour window and we could not leave anything to chance. We had a technical team on site at all times to check the quality of the material and laying process and also a Griptester to ensure the runway had sufficient skid resistance prior to opening the following day."

Midnight run

A normal night for Tarmac's 100-strong team involved gearing up in time to move onto the runway at midnight with planers, pavers, rollers, tractairs, sweepers, a bondcoat tanker and spare plant for every item in use. Planing was followed by bondcoat, laying of the macadam base, bondcoat again and then the Marshall binder course. The team would clear the runway so it could be fully inspected before the first flights at 6.30am, which landed on a new pavement course (this is normal practice, according to Fleetham). The Marshall surface course, grooving of the surface and white lining of that section would be carried out the following night.

"Our best nightly output was actually 1,400t of binder course, with no remedials on the contract throughout its duration," Fleetham says. "This is excellent considering it was carried out over a six-month period working nights in the winter."

Contract value: £10m

Client: Peel Holdings

Main contractor: Amec

Surfacing contractor: Tarmac National Contracting

Aggregate supplier: Tarmac

Bituminous products: Nynas Bitumen