Transcript podcast: How can 3D concrete printing accelerate the construction of houses?

Intro: You are listening to The Digital Engineer. In this podcast, we bridge the gap between our work as engineers and the digital world. In this three-part series, we update you on the housing challenge and how digital technology can help.
Pieter-Bas: Nice of you to listen to this podcast. My name is Pieter-Bas de Visser and in this series of 3 I talk to 3 specialists who each work on projects related to housing. Today I talk to Maartje Hoogeveen. She works as a structural engineer at Witteveen+Bos and she works in the Digital Construction team, where she is involved in innovations such as 3D concrete printing. Maartje nice to have you here, welcome.
Maartje: Thank you very much.
Pieter-Bas: Can you tell us a bit about your background? Where did you study?
Maartje: I studied in Delft, did civil engineering and as a master Structural engineering and from there I started at Witteveen+Bos as a structural engineer two years ago.
Pieter-Bas: Directly from your studies, nice. You are working on innovation within 3D concrete printing. Can you explain for the layman what that is exactly?
Maartje: Yes, 3D concrete printing is a new way of building, in which concrete comes out of a robotic arm layer by layer and with that you can build structures and the big advantage is that concrete is strong enough to bear its own weight and also the weight of the layers above it. So you no longer need formwork. That saves a lot of construction waste, you can lay the material wherever you want, so you have great freedom of form and you can also save a lot of concrete.
Pieter-Bas: Yes, what do we as Witteveen+Bos do in this? Mainly design work or what is our specialism?
Maartje: Our specialism is that we make designs. We also work a lot with the universities, with contractors with the governments to realise as many 3D concrete printed structures as possible.
Pieter-Bas: And what is your exact role in this?
Maartje: Well my role primarily is structural engineer. So I calculate the 3D concrete printed structures. What should the height be? What should the thickness be? Et cetera. And besides that, we do studies, we do tests to determine the capacity of 3D concrete printed beams. Those results need to be analysed and interpreted. That's what I'm working on.
Pieter-Bas: And if I remember correctly...If I remember correctly, we as Witteveen+Bos, not just in a consortium, have a printing site, are you often to be found there as well?
Maartje: Yes, we work a lot with that and with that we really realise concrete structures. We also do a lot of testing, so I can be found there sometimes, yes.
Pieter-Bas: And the way I know concrete, it always needs reinforcement as well. Is that printed along with it or is that applied afterwards? How exactly is that done?
Maartje: In that sense, it's really quite a different material actually than reinforced concrete. There are a number of ways to apply reinforcement. You can add fibres to the mix, small steel fibres. These give some extra strength to the concrete. We can also print just the formwork, right? So then you actually print a mould. You can put the reinforcement in there and still make reinforced concrete. You can also lay down rods in the layers while printing.
Pieter-Bas: Manually?
Maartje: Yes, or in the future maybe with a robot. So there are other solutions to still apply that reinforcement. We have realised a number of bridges, which are bicycle bridges with a span of 6, 7, 8, 9, 10 metres. It varies a little bit and then we pre-stressed the bridges, so then you actually compress the elements which again reduces the tensile stresses.
Pieter-Bas: And those elements are then printed in the print facility and then transported to site?
Maartje: Yes, actually a kind of pre-fab idea. There are also quite a few parties that print on location. I think that is also an important application of that printing, but is also a very big challenge. Concrete is a sensitive material. In the hall we have nicely controlled conditions, but on location we have weather and wind, so then it is a bit difficult to control the process properly.
Pieter-Bas: Yes, and compared to conventional reinforced concrete, what are the big advantages of concrete printing compared to current construction methods?
Maartje: I think it's a number of advantages. First of all, it's more durable, which I just mentioned, you don't need that formwork anymore. Often when you make a round shape, you make the formwork all the way around and then you can usually throw it away afterwards, because it's really made specifically for that object. You can lay the material down wherever you want, so you can make hollow sections instead of solid sections. That just saves you concrete. It also plays an important role in the housing task we have, because you can build very quickly with it. You can print an entire object in a few hours. So it's faster to build with it, also safer. One person has to turn on the robot. That is then controlled by a computer script and the robot does its job print the object and nobody has to pour concrete anymore.
Pieter-Bas: And you can go day and night.
Maartje: Yes, so it really does have a lot of advantages.
Pieter-Bas: There is also a trend going on about as far as wood in construction is concerned. Concrete is obviously not the most sustainable material. Well I understand that this means you need a lot less concrete by using the printer. But do you see this trend of wood construction as a threat to concrete printing, or are these things actually things that can coexist very well?
Maartje: Yes I think so. First of all, there are a lot of developments now in developing a more sustainable concrete mix, so with less cement, right? Because cement in that sense is the culprit in terms of CO2 emissions. That's what we call geo-polymer concrete. That's a different type of reaction, but more sustainable. And besides, wood is indeed a biobased material. Which grows, it stores CO2, but it's also a bit weaker. So if you need a very large span, concrete might be more convenient, because if you opt for a wooden floor, the floor height might become very large, making it still less sustainable. So I don't think there is a particular choice to be made. I think both play an important role in making construction more sustainable and, in that sense, they also stand side by side.
Pieter-Bas: Okay and going back for a moment to the normal printer I always used to print my book reports with. Yes, it also sometimes has no ink in between or a paper gets stuck. Do you also have these kinds of issues with the concrete printer?
Maartje: Yes, often enough. Well, often enough is not true, but there really are occasional problems that the pump might not work or that the material is too fluid or just too thick. And I think that's all part of that innovation. Also, do think that the role on the construction site will also change soon, right? Now we have a carpenter. Soon we will have an operator of the printer who keeps an eye on whether the printer actually does what we have asked.
Pieter-Bas: There should still be some kind of visual check on the construction process?
Maartje: Yes, I think so, but ultimately it does become safer, because accidents still happen in construction. Now the printer basically does the job.
Pieter-Bas: Then you indicate, you calculate those constructions. I can imagine a square building and maybe even a round building you can calculate through. But how should I see that with such a hugely organically designed structure?
Maartje: Yes, it is indeed very different. A 3D concrete printed structure is really a totally different structure than a reinforced concrete one. The material is very different anyway for reinforced than also structures we have standards. A lot of studies have been done in history, so we know how to design them safely. There are calculation rules for it, but for that 3D printed concrete, that doesn't exist yet. Those are in development, by the way. Which is very good, but now we have to prove the strength of structures by doing tests. First the very first bridge we had we tested 1-to-2 scale model all the way until it broke down. And so we actually went from coarse to fine again. Then we tested a bridge element. And then we only did a test very specifically to determine the shear force capacity for the bridge. Then we only really tested the material itself, with lots of small beams. So basically we really have to demonstrate the capacity and strength of the structures with tests.
Pieter-Bas: And so those standards are under development as you say, are we participating in that? Or who is developing those standards?
Maartje: Yes, we are also working on that. There are lots of parties doing research worldwide and that information is all being compiled.
Pieter-Bas: So there will soon be a handbook 3D concrete print building design? Drawn with Maartje. You also went to Singapore for this, I understood. What exactly did you do there?
Maartje: We purchased a printer there for the government and what they wanted was actually to investigate: How can we use 3D concrete printing to speed up our construction? They have a similar task to the one we have here in the Netherlands. There are a lot of people but not enough houses, so there they also want to build with fewer people eventually.
Pieter-Bas: Fewer construction workers?
Maartje: Fewer construction workers, and they want to see if they can automate that with 3D concrete printing, among other things. They bought that printer and got it working and printed a lot of objects actually and eventually also printed a prototype of a house. Really to show of, this is a very good method to do use for that housing development eventually. This was just one floor. They have houses of up to 20 or 30 floors there. But anyway, it's the beginning.
Pieter-Bas: And you brought your expertise in construction to that. Very nice and so now since two years at Witteveen+Bos, from your studies. Any specific reason why you chose Witteveen+Bos?
Maartje: Well, I did my graduation internship at Witteveen+Bos and that was, not entirely coincidentally, about 3D concrete printing. It was about a 3D concrete printed bicycle bridge and I looked at, how can we make the design of that bridge so that we can print it as quickly and as cheaply as possible? The printing process has a significant impact ultimately on the quality of that bridge and that concrete is of course very strong, isn't it? Because it has to be strong enough to support the layers on top, but that does go up to a certain limit. At some point it does start collapsing, because the concrete is still wet, so I found an optimisation in that of: How should we make those dimensions, the geometry of the bridge look, so that it can be printed as well as possible, but ultimately after 15 years still standing?
Pieter-Bas: Yes, so also when the next layer is printed on it, that the previous one has already hardened to the extent that it can bear it, but not too much, because otherwise it won't stick anymore.
Maartje: And then you just used unnecessary material.
Pieter-Bas: And what do you like most about your work?
Maartje: The thing I like most is that we are working on innovation. That is often very complex and very challenging, but therefore also very interesting and no day and no project is the same.
Pieter-Bas: Yes, that also makes it unique. How do you experience the construction world or at least innovation within the construction world? Are they ready for this or do you notice that there are still a lot of barriers to overcome before this becomes a tried-and-tested method?
Maartje: I think that construction industry is definitely aware that something has to change. In recent years, of course, the design process has become very digitised. We used to have a drawing board, now we work with 3D and 4D models. But yes, the construction process itself is still a lot of manual work, which makes a lot of sense. It is very complex. Every project is different. And we also have a lot of responsibility. We do actually make the constructions.
Pieter-Bas: It does all have to stay up.
Maartje: Yes, it does all have to stay standing, so I think the construction is definitely ready for it. But for the reason I just mentioned, it's also just pretty challenging because it's so complex and it needs innovation, but innovation is also exciting.
Pieter-Bas: Yes, it takes time.
Maartje: Yes and a lot of research and a lot of proven projects.
Pieter-Bas: You're on the Digital Construction team, a lot of innovation, digital engineer also which of course this podcast is about. Do you also notice that the role of the engineer is changing in that?
Maartje: Yes definitely, that's also one of the advantages of 3D concrete printing, isn't it? Because we control that robot with a computer model and eventually in the future I can see it then becoming that same model really becoming the basis for the design, where the architect can make the adjustments. The structural engineer can make adjustments and now that is quite often then has an iterative character and with that we can work together in that model much better and more efficiently.
Pieter-Bas: Yes so the roles become much more integral in that respect. And can you then also envisage that it, you mention it already that it is now quite iterative in design loops almost huh, does that then become a kind of continuous process? Do you envisage it like that?
Maartje: Yes, I do think continuous, but eventually you will always work from coarse to fine. But I think the coordination between the parties would run more smoothly, and eventually we can also send the design straight to the printer, which will hopefully also reduce the number of execution errors. Because that robot, it just does what it has to do.
Pieter-Bas: Well we are in the Netherlands, well known, facing a huge housing task is 3D concrete printing going to help us out here?
Maartje: Yes, I think so. We can build much faster with 3D concrete printing, as I said, with fewer hands, with fewer people. And we need to finish almost 1 million houses by 2030, so it could very well be that 3D concrete printing can play an important role in that. To actually make that task a reality.
Pieter-Bas: And what is needed for that? We obviously need to bring municipalities into that process. Are there still some bumps to be taken in the context of 3D concrete printing. Before we can actually start putting those houses down?
Maartje: So what would help a lot is what we just discussed as well, right? That standardisation, so that we can start standardising those designs. That would help a lot. I think that is the most important hurdle to take, so that the municipality can have those houses printed there with peace of mind. For that matter, so will the structural engineer himself.
Pieter-Bas: Is there anything in terms of laws and regulations that you guys are running into, of that's not allowed at all yet?
Maartje: No, not at all, as soon as you show that a construction complies by means of tests. That's really a part of the Eurocode, so in principle... you can do a lot and of course we work a lot together with the municipalities, the clients, we involve them a lot. That is also a very important part of this innovation, you know, that you really work together with all parties, so with the material supplier, with the contractor, but also with universities, but also with the clients.
Pieter-Bas: That all the ingredients are right. Then I can imagine that this innovation is actually quite all very fast, also certainly with robotisation. It always remains to be seen whether the government can move at that same speed, doesn't it? That it will soon all be applicable. How do you see your role within Witteveen+Bos in 10 years, for example, will it have changed completely by then, or how do you envisage it?
Maartje: In 10 years' time, I hope that we will have realised a lot more 3D concrete printed structures, which we can look back on. That we will also have gained a lot more knowledge from that and we will be working a lot more with 3D concrete printed structures, so when we design a new building, we will choose between reinforced concrete, made from precast elements or insitu, cast-in-place concrete. But there should also be an option there by default: we're going to print it. So I think my role is really still the same. Constructors are always needed, huh, to show that a structure is strong enough, but with many more many more options to also build more sustainably and build automated.
Pieter-Bas: Yes and will we need other colleagues in 10 years' time. And what will those colleagues be?
Maartje: Yes, we will need lots of people to help us make the designs, to control the robot. Architects, always installers. I don't think that will just go away, precisely because every building and every project is so unique and complex.
Pieter-Bas: Those roles are not just going to disappear, you think.
Pieter-Bas: Maartje, I want to thank you tremendously for the talk. Nice of you to be there. And dear listener until next time.
Outro: Nice that you listened to the digital engineer. Keep an eye on our channel for more episodes. This was a podcast by Witteveen+Bos.