Carbon reinforced concrete

US researchers have received $567,000 to explore how carbon fibres could improve the blast and impact resistance of conventional reinforced concrete.

Researchers at the Missouri University of Science and Technology have received $567,000 (£342,100) to explore how carbon fibres could improve the blast and impact resistance of conventional reinforced concrete.

The researchers, headed by Dr Jeffery Volz, the assistant professor of civil, architectural and environmental engineering, is being funded through a co-operative agreement with the Leonard Wood Institute.

Reinforcing concrete with fibres is not a new idea, said Volz. The Roman Empire used hair and straw in its concrete structures and Egyptians mixed straw in clay to make harder bricks.

Today, short carbon fibres – measuring no more than 1.5in – are found in buildings, bridges and slabs to limit the size of cracks. But in the future, Volz said that the carbon fibres could be up to 6in in length, significantly improving a structure’s ability to withstand blasts, hurricanes and other natural disasters.

‘The long fibres will absorb more energy as they pull out during the pressure wave or impact, cutting down on the potential for failure during an explosion or earthquake,’ Volz explained. ‘The fibres will also significantly diminish secondary fragmentation, reducing one of the leading causes of damage to surrounding personnel and materials.’

Emergency teams should then be able to get to the scene faster because they won’t have to clear chunks of concrete out of their way.

Previous efforts by other researchers to incorporate longer carbon fibres have failed for two reasons. First, longer carbon fibres are more likely to ball up as the concrete is mixed. Second, it is difficult to disperse the carbon fibres throughout the concrete.

Coating the fibres can reduce their tendency to form into a ball. The team plans to work on a variety of formulas to find a coating that balances between flexibility and rigidity. ‘A delicate balancing act is required to allow the fibres to flow easily during mixing, yet bond sufficiently with the concrete matrix in the hardened state,’ said Volz.

In addition, the team plans to study how a negative electric charge applied to a polymer coating could force the fibres to disperse more uniformly during mixing.