A group from the Vienna University of Technology has come up with a way of creating a domed concrete structure much cheaper and faster than current methods. Normally concrete domes are not built often because of the expense. Up until now to build a concrete dome, it was necessary to build a wooden structure to hold it in place. while the concrete hardened.
First you lay down a plastic bladder that can be inflated. Then you set out rebar on top of it and tie the rebar together. The rebar is laid out in pie shaped wedges. At this point, concrete is poured in and allowed to harden while it is all flat on the ground. Then the sections are all fastened together and cables attached.
There is an oval in the center which acts as the roof. Then around that but connected are the wedge shapes which have an empty channel between them.
Now, they start to slowly inflate the bladder to raise it into a dome structure. The concrete cracks some but supposedly is still structurally sound. Supposedly because the sections support each other, a bit like ice blocks in an igloo. Of course the rebar has to help as well. It must bend some as the the bladder is inflated. We also wonder if the concrete is raised before it is entirely hardened, but the article about the process didn’t say. They say the cracks are only small cracks.
As the bladder is being inflated, the cables are tightened. This apparently ensures that all the sections rise at the same rate. The article was less than clear as to why this was the case. After fully inflating the dome, the bladder is deflated and removed.
Then a layer of plaster can be coated over to help strengthen and to cover up the cracks. Seems odd unless the plaster is added to the inside. It seems like most of the cracks would be on the outside. But it doesn’t seem like plaster would hold up well exposed to the elements. The article could have been a bit more specific.
They built a test dome 10 feet high and the lead professor thinks they can create domes with a diameter of 160 feet or so without any problems. They think it will cut the cost of a building like this in half and also reduce time and material. Interesting idea but we would like to know a bit more about it before we trusted the process.