Tougher concrete speeds road repairs

Frequent or prolonged closure of road bridges for strengthening and maintenance could be significantly reduced following the development of a high-strength, fibre-reinforced concrete.

The UK’s road bridges are undergoing a strengthening programme, following EU and government decisions to progressively increase maximum lorry loads from 38 to 44 tonnes. This has caused disruption as concrete constructions are fitted with steel plating and carbon-fibre laminates. But if the concrete behind the strengthening material begins to disintegrate, the load falls on the strengthening which may result in a sudden failure and collapse.

CARDIFRC, developed by a team at Cardiff University, is more ductile that steel or carbon fibre. Stress will cause a gradual rather than sudden failure, allowing minor repairs to be carried out. Plates of the material can be cut with a diamond saw, and fitted using commercial adhesives.

The new material consists of concrete containing between six and eight per cent brass-coated high-strength steel fibres with a diameter of 150 microns and lengths of 6mm or 13mm.

Usually steel fibres used to reinforce concrete bunch together owing to strong electrostatic force. But CARDIFRC is made by reducing the amount of water used while ensuring fibres are uniformly dispersed, improving strength.

The university would not reveal its exact formula as it is still awaiting a patent. However, researchers say it involves simple engineering techniques.

‘The material has a bent strength of 30N/mm2 and a compressive strength of over 200N/mm2. Its toughness, or the energy required to break it, is at least 20,000 joules per mm2, making it a lot more resistant to cracks,’ said team leader and professor of engineering Bhushan Karihaloo.

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