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Vote of confidence

Highways Recycling

New performance specs are bringing recycling into the mainstream, say roads contractors.

One step at a time seems to be the Highways Agency's view of road recycling. 'Recycling has a huge future and can be as good as virgin material with regard to performance, but a big uptake will not happen overnight, ' says the Agency's senior pavement technical advisor Robert Dudgeon.

'New initiatives and technology take time to understand and the consequences could be dire if we take too big a leap at once.'

There are two key technical issues that need to be addressed - the quality of the material to be recycled and the type of binder added to make the rejuvenated asphalt mix work.

These have now been overcome, according to Nynas Bitumen, which claims to supply 50% of the insitu and exsitu recycling bitumen binder market.

'Trial projects have demonstrated just about every combination of exsitu and insitu methods with bituminous and hydraulic binders and many suppliers now regard long term trials as unnecessary, ' says special products manager Roger Dennison.

Local authorities seem to be getting serious about secondary aggregates and recycling. Roadstone Recycling is a long-time fan of exsitu recycling, and believes it has gained the confidence of major clients. 'Three exsitu jobs were carried out in Cumbria during 2003, including the first full motorway scheme on the M6, ' says managing director Gary Cook.

'But awareness of what's possible will be low until the detail is in the specs, ' he warns.

A 'cover all' performance based recycling specification may well be slotted into the Agency's Specification for Highway Works during 2004. The spec is being developed by transport research group TRL and is due to be launched this spring.

According to TRL's pavement design team leader Ian Carswell, the specification will contain specific clauses for the two principal exsitu and insitu methods and options for use of quick and slow curing hydraulic and viscoelastic binders. Crucially, it will also provide design curves that have been extended from 20M to 80M standard axles.

The specification is intended to be unbiased, but exsitu recycling is emerging as the more popular. 'Exsitu allows multi layered construction and greater control of the material than insitu alternatives, which are generally more suitable for smaller schemes, ' says Carswell.

Recycled base and binder courses account for a couple of hundred thousand tonnes in comparison to the 25Mt of new asphalt produced each year.

But Ringway Specialist Treatments in the guise of LCR Highways, its Lincolnshire County Council maintenance arm, is the latest convert. Having gained a taste for recycling using Roadstone Recycling as a subcontractor, the economics have justified the purchase of its own equipment.

'We are generating about 50,000t of granular waste each year at six storage sites and it is all being recycled for use as type one fill or Foambase asphalt, ' says LCR senior contracts manager Roy Hancock.

'The specification within our term maintenance contract now includes provision for use of Foambase. We expect to lay around 60,000t in the next three to four years.'

Insitu or exsitu?

Exsitu: Planings are transported to a crushing and mixing plant where the stone is screened to a designed grading and mixed with cement and bitumen 'foamed' through the injection of air and water.

Insitu: The top layers of worn out carriageway are pulverised to a depth up to around 500mm with rotovating plant which simultaneously adds water to bring the material to its optimum moisture content.

Calculated quantities of a bituminous or hydraulic binder such as cement, or a combination of both, are then mixed in before compaction.

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