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Carbon fibre bandages tried and tested say experts

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UK STRUCTURAL experts this week maintained that the practice of wrapping carbon fibre reinforced 'bandages' around concrete columns to prevent flexure and reduce the risk of bursting is a 'reasonably tried and tested' remedial method.

Failure of column heads is the suspected cause of structural failure in the collapse of Terminal 2E at Charles de Gaulle airport last weekend.

During construction of the Terminal 2E, cracking was noticed in some of the main column heads shortly after contractors placed the longitudinal beams which support the concrete vault.

It emerged that the tops of the columns were under-reinforced, and this was remedied by wrapping the top 500mm of each column with resin injected carbon fibre bands.

This work is now the focus of the investigation into what went wrong.

But the procedure is not new.

In the US and Japan, use has been widespread for more than a decade and applications in the UK date back around five years.

The Concrete Society published a guidance document on the method in December 2000 and UK experience includes car parks, bridges, offices and hotels.

Specialist subcontractors usually carry out work.

Care is needed to ensure surfaces are properly prepared and that the adhesive is spread evenly. One of the issues with the method is that after curing it is difficult to prove the bond between concrete and wrap is satisfactory.

The most common 'test' is to tap the cured wraps with a coin and listen for a dull tone - not easy in the middle of a busy airport.

Non-invasive specialist testing company Aperio has developed a thermal imaging test, but it told NCE that demand is limited and typically restricted to projects where the client is following best practice.

However, the company reports that where this test has been used, it usually identifies some areas of debonding; but stresses this tends to be in very isolated pockets and only over a small surface area.

Wrapping columns is considered a straightforward application, although experience with square columns, such as those used in Paris, is limited.

In this case, care is needed to avoid tearing the wrap on the sharp corners.

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