Carbon fibers improve blast, impact resistance of conventional reinforced concrete

Published 23 October 2009

Researchers find that adding longer carbon fibers to conventional reinforced concrete significantly improves a structure’s ability to withstand blasts, hurricanes, and other natural disasters

Researchers at the Missouri University of Science and Technology have received $567,000 (£342,100) to explore how carbon fibers 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 fibers 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 fibers — measuring no more than 1.5in — are found in buildings, bridges, and slabs to limit the size of cracks. Volz says that in the future, the carbon fibers could be up to 6in in length, significantly improving a structure’s ability to withstand blasts, hurricanes, and other natural disasters.

The long fibers 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 fibers 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 will not have to clear chunks of concrete out of their way.

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

Coating the fibers 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 fibers 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 fibers to disperse more uniformly during mixing.