A development that should have a major impact on domes for protecting mineral stockpiles is a revolutionary technique for their erection developed at the Vienna University of Technology. When concrete shells are constructed conventionally, they usually have to be supported by elaborate timber or other structures. This system now uses inflatable air cushions instead.
This completely new construction method does not require any timber structures at all: a flat concrete slab hardens on the ground, and then an air cushion below the plate is inflated, bending the concrete and quickly forming a sustainable shell. Even large event halls could be built this way, the University says. In Vienna, a first experimental structure has now been built using the new method.
“It is similar to an orange peel, which is regularly cut and then flattened out on the table”, says Professor Johann Kollegger. “We do it the other way around, starting with a flat surface and then bending it to a shell.” Johann Kollegger and Benjamin Kromoser (TU Vienna) have developed the new construction technique, which has now been successfully tested on the Aspang Grounds in Vienna.
At first, a flat slab is created using standard concrete. It is crucial to get the geometric shape exactly right. The slab consists of several segments. 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 center and pushed together from outside. To ensure that all the concrete segments move in perfect synchronicity, they are connected with metal beams. In the experiment, the whole process was finished after about two hours, the final height of the concrete structure was 2.90 m.
When the concrete is bent, many tiny cracks appear – but this is not a problem for the stability of the shell. “We can see that in old stone arches”, says Johann Kollegger. “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.