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Contractors World UK & Ireland
2012 Vol 2 No 3   
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Substantial cost and environment benefits on in-situ recycling repairs - page 3 of 3 >>>

Stabilised Pavements director Gerry Howe.

Stabilised Pavements director Gerry Howe.

Proven cold recycling techniques

The in-situ recycling process used on the eight Enfield tar-bound roads initially involved the top uncontaminated layer being planed off and disposed of as reusable road planings. Then the underlying damaged sub-base layers of each of the roads were broken up and rotovated by a special machine to a depth of 200 mm. A layer of cement, blended with pulverised fuel ash, was spread over the surface of the rotovated material.

The special in-situ recycling machine returned to rotovate and mix the cement and PFA blend into the material to full 200 mm depth, while at the same time water was added into the mix to produce the required optimum moisture content.

Any excess material was taken off site and mixed with crushed concrete before being used in the Borough’s roads and footways as Type 1 sub-base. The in-situ stabilised and strengthened material was then compacted with a roller, reprofiled and rolled again, prior to spraying the surface with a bonding tack coat and gritted so that the road could be temporarily opened to residential traffic. The recycled road was subsequently paved with a new 50 mm think surface layer and opened to full traffic.

The mix recipe for the recycled, stabilised and strengthened material was designed and determined from testing and analysing core samples taken from the tar-bound roads. The cement and PFA complement each other as the cement provides an initial gain in strength of the recycled road materials, while the PFA slows hydration and contributes to increasing the strength over time.

Roads in Enfield comprise of long straight through roads to narrow twisting residential streets.   The in-situ recycling at Enfield was carried out by the specialist road recycling and stabilisation contractor Stabilised Pavements Ltd, based in Lutterworth, Leicestershire.

Roads in Enfield comprise of long straight through roads to narrow twisting residential streets.
Photo: Christine Matthews

The company used its 500kW purpose built Wirtgen WR 2500 Cold Recycler, which is capable of pulverising to a depth of 320mm, to treat and stabilise in-situ nearly 13,000 m² in the eight roads and provide a 20 year design life for 0.5 million standard axles.

“I believe our in-situ recycling technique has to be the way forward for treating tar-bound roads in the UK, which also provides the additional bonus of a saving on CO2 emissions,” says Stabilised Pavements director Gerry Howe.
“This has been my first experience of in-situ recycling and anticipate using it on similar road strengthening schemes in future,” says Ian Sturrock. “Enfield is probably not alone with roads containing tar-based materials and this process could save other London Boroughs a fortune in disposal costs.

Up to a fifth of our budget could be spent on tar removal and that money, which would have been needed for disposal, can now be directed straight into treating and repairing in-situ failed, tar-bound roads. SPL has done an excellent job for us on these first roads that we identified containing tar and anticipate they will be returning in the spring to continue on the next programme of works.”

Click here fore more information >>> Stabilised Pavements Ltd

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