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New formula for high-strength shotcrete: Protecting tunnels from fires and terrorist attacks

Date:
May 5, 2015
Source:
Ruhr-Universitaet-Bochum
Summary:
Engineers have developed a shotcrete which is much more robust than traditional concrete. It can render tunnels, bridges and other constructions more resistant against fires and explosions. The new formula includes 140 kilograms steel fibers per cubic meter concrete – a figure that was thought to be impossible for shotcrete.
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In order to make the shotcrete more robust, RUB engineers add steel fibres into the mixture.
Credit: © RUBIN, photo: Gorczany

Engineers at the Ruhr-Universität Bochum have developed a shotcrete which is much more robust than traditional concrete. It can render tunnels, bridges and other constructions more resistant against fires and explosions. The new formula includes 140 kilogrammes steel fibres per cubic metre concrete -- a figure that was thought to be impossible for shotcrete.

Air bubbles make high fibre percentage in concrete possible

The new concrete owes its high protective capacity to its high steel fibre volume, plus the three kilogrammes of synthetic fibres which are added to the mix. "It used to be said that approx. 70 kilogramme steel fibres per cubic metre of concrete is as good as it gets," says Götz Vollmann from the Institute for Tunnelling and Construction Management. Larger volumes would render the material too rigid to be pumped through a hose and sprayed via a nozzle. His team's trick: foaming up the concrete until the mixture contains approx. 20 per cent air bubbles. "We assume that this process generates a ball-bearing effect of sorts," explains Vollmann. "The fibres presumable roll over the air bubbles, which makes everything smoother." The engineers add a defoamer to the concrete as it leaves the nozzle, which extracts air from the concrete within the fraction of a second.

New concrete can be applied to surfaces with complex geometries

Today, constructions materials do exist that can partly absorb the impact of explosions. Due to their manufacturing principle, however, they almost exclusively take the form of slabs, which cannot be used for cladding surfaces with complex geometries. The shotcrete from Bochum, on the other hand, can be applied to surfaces of any shape. In controlled blast experiments, project partners from the Fraunhofer Association's Ernst-Mach-Institut in Freiburg demonstrated the capabilities of this protective concrete: it accounts for as much as 60 per cent of the residual load capacity of the construction that has to be protected. To compare: the residual load capacity of unprotected concrete in the same experimental set-up reaches a mere 20 per cent.

Further information from RUBIN: http://rubin.rub.de/en/featured-topic-traffic/preventing-terrorist-attacks-shotcrete


Story Source:

Materials provided by Ruhr-Universitaet-Bochum. Original written by Julia Weiler. Note: Content may be edited for style and length.


Cite This Page:

Ruhr-Universitaet-Bochum. "New formula for high-strength shotcrete: Protecting tunnels from fires and terrorist attacks." ScienceDaily. ScienceDaily, 5 May 2015. <www.sciencedaily.com/releases/2015/05/150505082829.htm>.
Ruhr-Universitaet-Bochum. (2015, May 5). New formula for high-strength shotcrete: Protecting tunnels from fires and terrorist attacks. ScienceDaily. Retrieved May 28, 2017 from www.sciencedaily.com/releases/2015/05/150505082829.htm
Ruhr-Universitaet-Bochum. "New formula for high-strength shotcrete: Protecting tunnels from fires and terrorist attacks." ScienceDaily. www.sciencedaily.com/releases/2015/05/150505082829.htm (accessed May 28, 2017).

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