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Heavyweight breaker

Wrekin Construction has successfully completed a £3.6M 'crack and seat' carriageway reconstruction contract using a machine it developed itself. The firm used its new mobile guillotine to help rebuild 44,000m 2of the M54 in just 89 days.

Crack and Seat was developed in the US in the 1980s and arrived in Britain some years later. It was first used on a UK motorway in 1997. It has become increasingly popular as an alternative to the conventional reconstruction of concrete roads.

The method involves using a heavy weight to create cracks right through the concrete pavement. It leaves the concrete in pieces of sufficient size to provide enough structural integrity to act as either a capping layer or sub-base, allowing a bituminous or concrete surface to be laid on top.

Before developing its own machine, Wrekin carried out contracts using hired-in units but found them to be unreliable.

Managing director John Evans says: 'We have hired machines before and had breakdowns. On lane rental you can't afford to have the process stop. The Highways Agency want us off the road as soon as possible.'

When the contractor first got involved in this sort of work it tried using a demolition ball on the end of a 35t crane, but found the cracking it achieved was uncontrolled. The second step was to develop an oblong weight to replace the ball. 'It was fairly unsophisticated but there was some control, ' says Evans.

Wrekin then looked at a job that would have required two machines with that capacity, and decided the time had come to 'let the mechanical people loose on it'.

The result is a large guillotinestyle weight mounted on the body of an old blacktop paver. The 2.6m wide falling blade has a variable weight of up to five tonnes, and can induce cracks through the full thickness of a concrete carriageway in a single blow.

The key difference between Wrekin's machine and others lies with the control system. The blade is raised by a hydraulic ram and wire cable, and is activated by an air valve. Evans says this will result in far fewer breakdowns, as the system will not be affected by vibrations from the falling weight.

The contractor spent £20,000 developing the guillotine breaker and believes there is enough work of this type coming up in the UK to justify the construction of a second machine.

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