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M25 tries out combination topping

A UNIQUE hybrid form of road construction will be tried for the first time on a deteriorating section of the M25 south of London between Junction 5 and the Clacket Lane services.

Fitzpatrick has been awarded the £11.7M contract to reconstruct 7km of unreinforced concrete road built in the late 1970s. Highways Agency civil engineering group manager Graham Bowskill said the road was 'very tired' despite surface dressing in 1990 and an extensive programme of vacuum grouting intended to stabilise the concrete slabs.

'We carried out a value engineering exercise with our agent WS Atkins to determine the best way of achieving a 40 year life for the road, ' Bowskill explained.

'A number of options were looked at, including complete reconstruction, but the chosen solution has less than half the whole life costs of complete reconstruction and will take 16 weeks rather than 50.'

A high strength 200mm thick continuously reinforced concrete pavement will be laid on top of a 12mm layer of bitumen applied directly to the inner two lanes of the existing concrete road. A 30mm high performance bituminous wearing course will be laid on top.

The outside lane, less prone to rutting, will be levelled up with 212mm of bituminous roadbase topped with the same wearing course.

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