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New balloon method to build large concrete shells

June 16th, 2014

A new construction technique to build large concrete shell structures has been developed by scientists in Austria.

pneumaticwedgemethod-6-190x126The “balloon” method does not require any expensive supporting structures which have previously put developers off building large concrete shells.

The technique devised at the Vienna University of Technology uses a flat concrete slab which hardens on the ground before an air cushion below the plate is inflated bending the concrete and forming a sustainable shell.

Professor Johann Kollegger said: “It is similar to an orange peel, which is regularly cut and then flattened out on the table.

“We do it the other way around, starting with a flat surface and then bending it to a shell.”

A flat slab is first created using standard concrete.

Kollegger said It is crucial to get the geometric shape exactly right.

The slab consists of several segments and wedge-shaped spaces are left between these segments, so that the segments fit together perfectly when the structure is bent.

Once the slab is hardened, an air cushion below is inflated. The cushion consists of two plastic sheets welded together.

At the same time, a steel cable is tightened around the concrete segments, so that the concrete is lifted up at the centre and pushed together from outside.

To ensure that all the concrete segments move in perfect synchronicity, they are connected with metal beams.

In the first trial the whole process was finished after about two hours and the final height of the concrete structure was 2.90m.

When the concrete is bent, many tiny cracks appear – but this is not a problem for the stability of the shell.

Kollegger said: “We can see that in old stone arches.

“If the shape is right, each stone holds the others in place and the construction is stable.”

In the end, the structure can be plastered, then it has just the same properties and is just as stable as a concrete shell constructed in a conventional way.

Kollegger said the method could be used to build shells with a diameter of 50 metres.

He added: “As the new construction method renders timber structures obsolete, it not only helps to save time and resources, it also saves a lot of money.

“About half of the construction cost can be saved – even more in large structures.”

The new construction method has already been patented and trialled by the Austrian Federal Railways to build a deer pass over two high speed rail tracks in Carinthia.

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