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Concrete transformers

Precast systems - Versatility is the watchword for a new precast concrete system.Dave Parker finds out more.

Only two basic units make up the precast concrete Karapace system - a 3.15t trough shape and a near 2t flat wall panel. But such is the ingenuity of the concept that the units can be joined in a bewildering number of combinations with an astounding list of potential end uses.

Building consultant Nigel Maydew will demonstrate many of these at the drop of a hat.

In his briefcase he carries neat 1:20 plastic scale models of the basic K1 and W1 units, and in his hands these snap together into retaining walls, jetties, culverts, motorway safety barriers and much, much more. An agricultural engineer by training and an inventor by inclination, Maydew has been working with Bristol based precaster Milbury Systems on the Karapace concept since 2004, and the first contracts are now in progress.

Karapace was launched at NCE's Civils 2005 show last November, and there 'we attracted attention from a remarkably eclectic range of potential customers', Maydew reports.

'These included the military, who were looking at blast walls and bunkers, people who were planning a marina in the Grenadines, and someone who thought Karapace might be just what he needed for storm water drainage in the Middle East.' The original concept was a precast walling system for earth retention and slope stabilisation that would require minimal foundations and would make maximum use of as-won materials for stability. 'It doesn't work like gabions or blocks, ' says Maydew. 'A better analogy would be expanded metal sheeting laid on its side.' Made of C50/60 concrete in steel moulds, the two units are linked together by steel rods dropped into holes. Erection is simple; so is disassembly, so Karapace can be used over and over again for temporary demountable structures such as winter flood defences. For permanent structures the linking rods are grouted up after assembly.

Start playing with the models, and the system can take on many forms. Two lines of trough and panel units back to back could be a jetty or a railway platform. 'Interlocking' the two lines narrows the footprint, turning Karapace into a safety barrier for the central reservation of motorways - or temporary security barriers around embassies or similar potential terrorist targets.

'All these applications share the same benefits, ' says Maydew. 'On normal ground no foundations are needed, and erection is simple and quick.

If appearance is important, Karapace can be produced with a range of surface finishes, but the standard finish is high quality anyway.' Turning the system through 90- opens up even more possibilities, he adds. Set on its 'back', the K1 unit immediately becomes a drainage channel.

Topped with another K1, the resultant hexagonal duct can offer protection to sensitive services. Add horizontal W1 wings to the K1 drainage channel and a canal with 'towpaths' appears. More complex arrangements yield sophisticated culverts.

'The units are designed with a standard 15mm gap between them, ' Maydew says. 'This is easily sealed with any of a wide range of materials to produce a watertight structure.' He adds that the most interesting Karapace contract at the moment is in Wales, where it is being used to stabilise a slate waste scree looming over a new lorry park. No foundations or imported material are being used, a feature of Karapace that is attracting a lot of attention from the railway sector.

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