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Two giant 'concrete ears' planned for opposite sides of the English Channel are setting a stiff challenge for the UK precast concrete industry.Devised by sculptress Lise Autogena, the acoustic mirror project is designed to act as a symbol of the link between the twinned towns of Folkestone and Boulogne.

When complete, visitors will be able to stand at the focal points of the mirrors and talk directly to each other across the Channel. Autogena explained that this would need electronic assistance, due to the high level of ambient noise in the Channel.

Autogena drew inspiration from the series of insitu concrete acoustic mirrors constructed along the south coast during the 1930s. These were intended to give early warning of air attack, but were overtaken by technological developments such as radar.

Structural engineer B Consultants designed the 7m diameter hemispherical mirrors to be made up of precast lightweight concrete segments.

'We need the segments to be cast to an accuracy of no less than +/-3mm, ' B Consultants technology director Richard Harrison explained, 'And +/1mm would be even better.'

Harrison said eight leading precasters had been contacted in the last two months, and two had expressed serious interest.

'The problem is the cost of the moulds, which could run into hundreds of thousands of pounds, ' he added.

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