Bomb-proof concrete

Clay Technology magazine
13 Feb 2009
A cracked section of the fibre-reinforced concrete

A high performance concrete designed to reduce the impact of bomb blasts is being investigated by engineers at the University of Liverpool, UK.

The fibre-reinforced material has already been employed in the design of slender footbridges and government buildings in Australia, but has yet to be used in the UK. Other applications include bomb-proof litter bins and protection barriers.

The material has a high cement content, low water/binder ratio and uses fine silica sand as its only aggregate. Short, straight steel fibres with a high compression and tensile strength in the region of 1,800 and 2,000N/mm2, respectively, reinforce
the material.

‘Concrete barriers can be dangerous if subjected to intense explosive loading, as they are susceptible to back-face spalling and can create flying shrapnel, one of the most lethal consequences of bomb-blasts,’ explains Professor Steve Millard, lead scientist on the project at Liverpool. ‘The fibre-reinforced material is different because needle-thin steel fibres added into the concrete mix provide a better bonding action than conventional steel reinforcing bars, increasing its tensile strength by 10 times’.

The material, produced by Lafarge, a Paris, France-based building materials company, is formed in a conventional concrete mixer, but requires curing at an elevated temperature of 90°C to improve the microstructure and increase strength.

University engineers, working in partnership with the UK Centre for the Protection of National Infrastructure, have explored the limits of the material’s capabilities with a series of high explosion blast tests at RAF Spadeadam in Cumbria.

‘We gradually reduced the distance to the explosive charge to examine the concrete’s bending strength and capacity to absorb energy,’ says Millard. ‘The material resisted the explosions without any disintegration from the back of the panels causing shrapnel.’

Concrete and cement science specialist Dr Charles Fentiman of Fentiman Consulting, based in Horsham, UK, can see a number of potential uses for the material, but argues that steel plates could provide a more cost effective solution.

However, while Millard agrees that a solid steel plate will have a similar blast/impact resistance, he argues that steel cannot be cast easily to any shape. ‘The fibre-reinforced concrete can be cast without the need for specialist facilities or handling,’ he adds.