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Contractors race to replace Wadesmill black top

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A MASSIVE recovery operation is under way on the troubled £25M A10 Wadesmill Bypass in Hertfordshire, where up to 7km of newly laid dual carriageway may have to be totally reconstructed.

Contractor Fitzpatrick has already removed nearly 10% of the road and the Highways Agency has confirmed that at least 25% will have to be replaced.

Heave resulting from sulphate attack on the lime stabilised capping layer is blamed for the problems (NCE 11 March).

Material from the site was mixed with quicklime to form the capping layer and was used under almost all the construction.

An intensive testing programme is still under way to locate any sulphate concentrations that could still attack apparently unaffected stretches of the roadway.

Above the 300mm thick capping layer was 150mm of Type 1 sub-base and 300mm of asphalt base and wearing courses. Fitzpatrick is planing off and stockpiling the blacktop, separating out the subbase and crushing the central concrete channel for recycling.

The contractor originally expected to open the bypass eight months early. Lime stabilisation of site-excavated material was seen as a 'winwin' option, saving time and money as well as minimising environmental impact.

Fitzpatrick hopes that existing on-site trials (see box) will allow it to recycle as much as possible of the 6,000t or more of blacktop and other materials it will have to replace.

Otherwise it will have to dispose of this and import virgin materials instead. If this happens Fitzpatrick will struggle to meet the official August opening date.

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