#3: Houses from the printer

Georg Hansemann at the Roboter Design Lab. © Lunghammer - TU GrazGeorg Hansemann at the Roboter Design Lab. © Lunghammer - TU Graz

Will we soon be able to print out houses with a printer? Georg Hansemann, who works on 3D printing of components in the Robot Design Lab, answers these and many other questions.

Talk Science To Me is the most curious science podcast in the podcast world - but especially at TU Graz. We ask the questions, and our researchers provide the answers. From artificial intelligence to sustainable construction and on to microorganisms that feed on CO2 to produce proteins... it’s all found here! Listen in and be inspired.
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Welcome to the TU Graz science podcast Talk Science to Me. It’s great that you are with us again today. Today it’s all about a very exciting topic in the field of sustainable construction: 3D printing with concrete. The central question: Will printers soon be able to build houses? My guest today is Georg Hansemann. He is a doctoral candidate at the Institute for Structural Design and is working on his dissertation with the printing robot in the Robot Design Lab in Inffeldgasse in Graz.

Talk Science to Me: Hi Georg! Welcome and thank you for answering my questions today. You are working in the Robot Design Lab with a printer that can print out concrete. The goal is to use it in architecture and construction. Will the printer soon be able to print out houses?

Hansemann: In recent years, there has really been an increasing interest in research and industry, and 3D printing with concrete has taken a big step forward in development. It can already support the construction industry to print or implement houses cheaper, faster, more sustainable. At the Institute for Structural Design, however, we are not pursuing the approach of printing entire houses, but rather concentrating on specific construction elements, then implementing them in the laboratory as in the precast plant, and then delivering them to the construction site as precast or semi-precast parts.

You already mentioned sustainable construction. Where is the sustainability aspect - How can you make construction more sustainable using 3D printers?

Hansemann: Using 3D printers, we can make construction more sustainable by designing smarter building structures. It is often the case that very simple concrete formwork is erected for reasons of time and simplicity. The concrete is poured in, conventionally reinforced, and no attention is paid to optimising the structures because it is simply too time-consuming and costs too much money. And 3D printing can help and, through complex special shell construction that is nevertheless economical thanks to the robot, can help us get back to more complex structures or more intelligent concrete construction. We also always talk about the 3D printer being a formwork printer. We use these objects with low wall thickness as formwork, which are then used in conventional structures and take out all the concrete that is not needed.

How would formwork be built in the classical way?

Hansemann: We have an application area here - for example the ceiling, which is treated very extensively as a research area and a large square metre number of flat ceilings are installed worldwide. And these flat ceilings are not really intelligent. A lot of material is used here that is not even needed from a structural point of view. But it is done anyway because it is simply economical. You have a simple formwork on the construction site. The implementation is very easy. You can reinforce it conventionally. And then simply pour it in completely. And for time reasons, one refrains from building complex formwork conventionally. Because it’s not economically justifiable and that’s why you have all these monolithic components. And the 3D concrete printing itself makes the whole thing more economical again. So we can simply plan these formworks, these complex formworks, digitally, print them out and install them on the construction site. In the case of the slab, these are then simply placed on a slab formwork, are then conventionally reinforced and are then poured with concrete. And we thus convert all the flat ceilings into ribbed ceilings, which are much more material-efficient. Here we achieve a material saving of not infrequently 40 to 50 percent.

You say more complex structures and you can then make ribbed ceilings from a normal smooth ceiling. What shapes are possible with the concrete printer?

Hansemann: In the research project we always test out how far the technology can go. We often do this in workshops with students. We start by printing vases, tables, wall panels, acoustic panels and complex structures, where we can test the printing process and the material, which requirements they can meet and which shapes are possible.

When I get into the Robot Design Lab, what do you have there? What do I see there?

Hansemann: This robot design lab consists, as the name suggests, more or less of a robot. This robot is an industrial robot from ABB and it stands on a linear axis that can move six metres. And has a construction area of six metres by one metre fifty. And two metres in height.

Is this a normal robot that you can buy and that can already 3D print? Or did you have to develop something new?

Hansemann: Well, the 3D concrete printing system as it is found today did not exist as a ready-made system that could be modified. Instead, most of the system components had to be developed from scratch. The only things that already existed were the industrial robot from ABB and the mortar mixing pump from the company Mai. We had to develop the material, for example, because normal concrete is not suitable for 3D printing. A conventional concrete is usually poured into moulds where it can harden. And with 3D printing, the material itself must have the property of building up in layers and staying in shape. In addition to the material, we have developed all the other components that are necessary for the printing process. Starting here with the mortar mixing pump, which already existed, but which we had to modify to such an extent that we reduced the material flow and adapted it for 3D printing. Then we developed a nozzle that is mounted on the robot, where the material, which has to be very pumpable and have long open times so that it is practicable, has an accelerator added to the nozzle so that when it leaves the nozzle, the material can be deposited on a print substrate in a stable shape.

How should I imagine the material? Is it very different from the conventional concrete?

Hansemann: The printed concrete can no longer be compared to normal concrete. In the beginning, we tried to print normal concrete. But we saw right away that it doesn’t work. Over the years, we have developed the material further and further. Now we have to intervene and say that we don’t print with concrete. For definition reasons, it is actually a mortar. Because we have a maximum grain size of two millimetres in the material and that’s when we actually talk about a print mortar and no longer about concrete. And this printed mortar must have certain properties that normal concrete, when it is tipped into a formwork and left to harden for several days, does not have to have. On the one hand, this printed concrete must be very easy to work with. We pump this mortar with a mortar mixing pump to the nozzle, so it has to be very pump-resistant. When we are not printing and the printing plant is at a standstill, the open times have to be very high so that the concrete does not harden and set in the material hose. That is another property that print concrete has. And then it has to harden again very quickly at the nozzle. Because when it leaves the nozzle, it must be able to be deposited on the print substrate in a dimensionally stable way. And we achieve this by adding an accelerator to the print nozzle. This then reacts with the concrete and as soon as it leaves the nozzle it is dimensionally stable and can be layered.

So as soon as it’s printed, I can take the part with me?

Hansemann: You can’t take it with you straight away. You are very surprised during the printing process that it hardens so quickly and can be built up in front of you in such a stable shape. But you have to wait a bit. You can manipulate it and move it around with the print background. But you can only really lift it off the print background after a few hours. Which is still very fast compared to poured concrete, where you sometimes have a stripping time of 20 days.

How does the printing process work in total? Let’s say I want a table, I know what I want it to look like, I come to you and ask you to print that table. What happens then?

Hansemann: With this design developed, we can then design the print paths. This is then simply a 3D model that is broken down into layers and these layers are a continuous path that the robot can be taught to follow precisely. So the object can be built up precisely. And then we would actually start the machine. So we would load the mortar pump with dry material and we would mix this dry material with water. This is then pumped up to the nozzle. There, as already mentioned, it is mixed with an accelerator and then this concrete strand can be built up in these layers.

It’s basically like a long thread coming out of the concrete printer. What does the finished product look like then? Is it a smooth wall?

Hansemann: Quite the opposite. It is not a smooth wall. It is divided into layers by this strand and you can see that in the end product. And it has a certain roughness. But in the end, you can design very well with this roughness and these layers. In these façade panels, we have the possibility to reproduce a variety of textures. That is a great advantage of additive manufacturing, because it is built up in layers. So you can design each layer more or less separately. In other words, you can influence it with speed and with additional material and create structures or textures that are also very interesting for architecture. Very complex patterns are possible that would be far too costly with a complex formwork. You can intervene during the printing process - you don’t just have to run straight lines and can do zigzag lines, for example. And this creates an even rougher surface on the whole object, but one that has a system in itself and comes across in the pattern.

Have you already implemented real projects and used real concrete-printed parts in buildings?

Hansemann: Yes, I have already had the opportunity to implement the construction method at the Institute together with my colleagues. One project was together with the client Hans Kuppelwieser at Schloss Seehof in Lunz am See. And another project was in Nördlingen together with the company Eigner Bau, where we built an underground car park for a residential building.

How exactly did this construction go?

Hansemann: As I said, in cooperation with Hans Kuppelwieser, we designed a ceiling or a studio roof in the first project in Lunz, where this technology is used. And we reinterpreted this construction method, which we had already tested in the research project, where we printed recesses that we then placed normally on the formwork in order to save concrete. Not only did we produce an orthogonal and regular ribbed slab or roof, but we also intervened in terms of design. In the robot design lab we then produced the 3D printed bodies, our recess bodies, which were then used on the construction site and took concrete out of the structure. Here we were able to save 40 per cent of material and find a very successful solution for the studio roof.

Are there any current projects you are working on?

Hansemann: We are currently working on a ceiling in Bludenz, Vorarlberg. Together with a construction company, we are building a ceiling for a building materials yard. We are already in a much larger area. This ceiling has a dimension of 600 square metres.

Approximately how long does it take to finish something like that?

Hansemann: In the case of Lunz, we printed 130 recess bodies and had an effective printing time of 18 hours. Of course, that is divided into several days, but you have a certain benchmark to which you can adhere. In the construction project in Bludenz, we have 640 recess elements, which are a bit larger. So the time is multiplied considerably.

Where do you have the feeling that further work should be done? Where could you still optimise? Or what are the big research questions you still have?

Hansemann: It is clear that the construction process needes to be optimised. We have questions of logistics and reinforcement that have to be handled better. At the moment in Lunz, we have tried and tested the project ourselves. We got to know the whole process, we got to know the construction site and we got to know that reinforcing the complex geometry is very complex. System solutions have to be found here, and that’s why we’re doing more projects. Like the project in Nördlingen or the project in Bludenz, where we are also working out such systems together with a reinforcement company in order to minimise construction times. In the area of façades, we are working very hard on the integration of a probation system. Here, very thin-walled façade panels are implemented, which would not hold on their own without probation. For safety reasons and also for static reasons, a reinforcement must be inserted there.

How can you do that, for example, that you integrate a reinforcement there?

Hansemann: So in our case: You print an infinite concrete strand and we want to carry the reinforcement with us. So the most obvious thing to do was to integrate a reinforcement in the middle of the concrete strand. And this then runs along during the process, forms a bond with the concrete and can better absorb the tensile forces that arise in the structure.

Just so I understand it correctly: The reinforcement then travels the exact paths that the concrete travels during printing?

Hansemann: Exactly, the reinforcement is carried along, maps the same paths and therefore you have to plan the structures better. So that the forces can be absorbed in both directions and not only in the horizontal layers.

What do you personally find so exciting about the topic that you deal with it so intensively?

Hansemann: It is a very multi-layered subject where you can further your education in many areas. In addition, the balance between printing in the lab, working in front of the computer, working on the construction site and interacting with students in workshops is a very good one, which I personally like a lot.

Money is always a very big issue in research. If it was not at all, what would you implement?

Hansemann: If money were not an issue, I would wish that these potentials of 3D printing would be used much more often. For example, in the areas of ceilings, walls and foundations. There is potential everywhere to take out material. And construction companies often shy away from making changes there and changing structures. And with the possible money, you could build up a certain leverage here that would then lead to this being implemented.

Do you feel that 3D printing can and will be used on a large scale in construction?

Hansemann: The ceiling application already has the potential to be used on a large scale. The flat ceiling is a very popular construction method. And because it is very easy to plan and implement, it is installed in a large number of square metres. And these could already be optimised with a small amount of effort using 3D printing. And our implemented objects show that it is already possible to save material in the near future and to approach the construction of our supporting structures in a more resource-saving way.

Then we are very curious to see in which direction the development will continue. Thank you very much for being our guest today and answering my questions!

Hansemann: Thank you very much!

Talk Science to Me: And thanks again to all of you for being there! We’d love to hear from you again next time!

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