Latest / The Manufacturing Podcast with Fexingo: Factories, Supply Chains, and Industrial Business / How a German Factory Is 3D Printing Houses with Recycled Concrete
Transcript
- Lucas: So there's a factory in Beckum, Germany — small town east of the Ruhr — that is printing load-bearing walls from demolition rubble. Not prototypes, not showpieces. Actual walls going into apartment buildings. Luna: I've seen the 3D-printed house videos — the robot arm squirting out concrete like a giant icing bag. But using recycled aggregate? That's different. Lucas: Exactly. The company is Peri — they're known for formwork systems, the molds you pour concrete into on a construction site. They've been in that business for over fifty years. But they saw the writing on the wall: formwork is labor-intensive, it's wasteful, and for complex shapes it's hugely expensive. So they started a 3D printing division. Luna: And they're printing with recycled concrete? How does that even work structurally? Lucas: They take crushed concrete from demolition sites — old parking garages, office blocks — and they grind it into an aggregate with a specific particle size distribution. Then they mix it with a geopolymer binder instead of Portland cement. The binder is the key innovation. Traditional cement is responsible for about eight percent of global CO2 emissions. Geopolymers use industrial byproducts like fly ash or slag, and they cure through a chemical reaction rather than the high-heat process that makes cement so carbon-intensive. Luna: So you're cutting the embodied carbon from the binder. But what about the recycled aggregate — does it have the same compressive strength? Lucas: That's the engineering challenge. Recycled aggregate is more porous, it has micro-cracks from the original crushing. But Peri found that if you optimize the particle gradation — meaning the mix of coarse and fine particles — and use a geopolymer that bonds chemically with the old concrete, you can actually exceed the strength of standard C30/37 concrete. Their printed walls reach about 45 megapascals after 28 days. Luna: That's impressive. But I remember reading that 3D-printed concrete often has issues with layer adhesion — the weak point between the printed beads. Lucas: Yeah, that's the classic failure mode. If the time gap between layers is too long, the surface dries and you get cold joints. Peri's gantry printer — it's a large frame that moves on rails — prints at about 10 centimeters per second, and the nozzle is designed to keep a continuous bead. The machine lays down layers that are about 4 centimeters tall and 6 centimeters wide. The key is that the printer doesn't stop between layers; it does a continuous spiral pattern for the wall, so there's no horizontal joint. Luna: Continuous spiral — so the wall is essentially one long strand of concrete coiled up like a pot? Lucas: That's the visual. And because it's a 3D shape, you can optimize the wall geometry. You don't need a solid rectangular cross-section. You can print a honeycomb interior, or a zigzag pattern that uses less material while maintaining strength. Peri claims their printed walls use about 60 percent less concrete than a traditional cast wall of the same structural capacity. That's the headline number. Luna: Sixty percent less material — that's massive. But what about the printer itself? How big is this thing? Lucas: The gantry at the Beckum factory spans about 20 meters by 10 meters by 6 meters tall. So it can print walls up to 5 meters high. The print head moves on three axes, and there's a fourth axis for the nozzle angle. It looks like a giant CNC machine, but for concrete. The whole setup was developed in-house by Peri's R&D team over about four years. Luna: And is this actually being used on real construction sites, or is it still in the testing phase? Lucas: Real projects. They printed a two-story apartment building in the town of Wallenhausen in 2024. That was the first multi-story residential building in Germany with load-bearing 3D-printed walls. Since then they've done a few more — a single-family home, a small office extension. The apartments in Wallenhausen are occupied. People live there. Luna: So the technology is past the 'look what we can do' stage. But what's the economic case? If the raw material is recycled and the labor is automated, is it actually cheaper? Lucas: The raw material cost is about 15 percent higher than conventional ready-mix concrete, because the geopolymer binder is more expensive than Portland cement, and the recycled aggregate requires more processing. But the big savings come from eliminating formwork. For a standard rectangular wall, formwork accounts for about 30 to 40 percent of the total concrete structure cost. For complex geometries like curved walls or integrated window openings, that can go even higher. With printing, you don't need any formwork. So for complex shapes, the total project cost can be lower than traditional methods. For simple straight walls, it's still more expensive. The sweet spot is anything with non-standard geometry. Luna: Makes sense. But there's also the speed factor, right? How fast can they print a wall compared to pouring and curing? Lucas: The actual printing time is fast — a typical house wall section might take two to three hours of print time. But that's just the deposition. You have to consider the setup: the gantry needs to be assembled on site, the concrete mix needs to be calibrated, and the printer needs a continuous supply of material. The real bottleneck is the concrete itself — it has to have the right rheology to be pumped and extruded without sagging, but also set quickly enough to support the next layer. Peri uses a mix that has an open time of about 30 minutes, meaning it stays workable for half an hour, then stiffens. So the printer can run continuously, but if there's a stoppage, you can't just pause and restart — you'd get a cold joint. Luna: Right, so it's like a just-in-time manufacturing process. The concrete arrives and it has to be used immediately. Lucas: Exactly. And that's where the logistics get tricky. The factory in Beckum is a central mixing plant — they produce the geopolymer concrete and truck it to the construction site. But for larger projects, they're considering mobile mixing units that can be set up on site. That's still in development. Luna: You know, this reminds me of something we've touched on before — the tension between innovation and regulation. Germany's building code is famously conservative. How are they getting these walls approved? Lucas: That's the biggest hurdle. German building law requires a general building approval, or allgemeine bauaufsichtliche Zulassung, for any construction method that deviates from the standard. Peri had to go through a multi-year testing process with the German Institute for Building Technology to get approval for their printed walls. They had to demonstrate fire resistance, sound insulation, load capacity — the whole battery. They finally got a national technical approval in 2023, but it's specific to their system. So each new project still requires individual approval from the local building authority. Luna: So it's not like you can just buy the printer and start printing walls tomorrow. There's a regulatory moat. Lucas: A very deep moat. But that also protects Peri's position. They're one of the few companies with an approved system in Germany. There are competitors — COBOD in Denmark, ICON in the US — but they use different materials and processes. Peri's advantage is that they have the formwork legacy, so they understand the construction industry's requirements. They're not a tech startup trying to disrupt; they're an established manufacturer adding a new capability. Luna: That's a smart framing. It's not about replacing concrete — it's about reducing waste in concrete construction. Which brings me to the environmental angle. If you're using recycled aggregate and a geopolymer binder, and you're using less material overall, what's the carbon footprint per square meter of wall? Lucas: Peri published a life-cycle assessment for the Wallenhausen project. Their printed walls had an embodied carbon of about 120 kilograms of CO2 per cubic meter of wall — compared to about 300 for a standard cast concrete wall with Portland cement. So roughly a 60 percent reduction. The majority of the savings come from the binder — geopolymers have about 80 percent lower emissions than Portland cement — and the rest from material reduction. But you also have to factor in the printer's energy use and the transport of the recycled aggregate. The net is still significantly positive. Luna: And what about end of life? If the wall is made of recycled concrete, can it be recycled again? Lucas: In theory, yes. The geopolymer binder is chemically different from cement, but it can still be crushed and used as aggregate in a new geopolymer mix. The challenge is that the recycling stream would need to be separated from conventional concrete waste. That's a sorting issue, not a technical one. Peri is working with a local demolition company to create a closed-loop system: they take the rubble from old buildings, process it into aggregate, print new walls, and at the end of the building's life, the walls go back into the same process. Luna: So essentially, the building becomes a material bank. Lucas: Exactly. That's the long-term vision. But right now, the volume is tiny. Peri's Beckum plant can produce about 100 cubic meters of printed wall per year — that's enough for maybe two or three houses. They're scaling up, but it's slow. The real breakthrough will come when the cost curve crosses over for simple geometries, not just complex ones. Luna: And when building codes catch up. If you're a developer, the uncertainty around approval is a dealbreaker. Lucas: Right. It's a chicken and egg problem. More projects would lead to more data, which would lead to faster approvals, but you need approvals to get projects. Peri is trying to break that cycle by doing demonstration projects and publishing results openly. They're also working on a standardized wall design that could be pre-approved for multiple sites. Luna: Before we go into the future of this, I want to shift gears slightly. You know, I've been thinking about this podcast itself. We spend a lot of time talking about factories and innovation, and we don't run any ads. That's a deliberate choice — we want the conversation to be uninterrupted. And we've had listeners ask how they can support that. There's a simple way: if these episodes have helped you think differently about a business problem or given you a concrete example to share, you can support the show at buy me a coffee dot com slash fexingo. That's buy me a coffee dot com slash f-e-x-i-n-g-o. It's not a subscription or anything — just a way to say 'keep going.' We appreciate it. Lucas: Yeah, that's exactly right. It's a listener-supported show, and that's how we keep it ad-free. So thank you to anyone who's contributed. Now, back to Peri — I want to talk about what's next. They're not stopping at walls. They've started experimenting with printing floor slabs and even staircases. The printer can handle any geometry that fits within the gantry envelope. The challenge with floors is that you need to incorporate reinforcement — steel rebar — which is hard to do in a continuous print. They're working on a system that places rebar robotically between layers. Luna: So it becomes a fully automated construction system. Robot places rebar, robot prints concrete, robot smooths the surface. The human role shifts to design and oversight. Lucas: That's the trajectory. But I think the more immediate impact is in infrastructure — things like retaining walls, noise barriers along highways, or drainage channels. Those are often repetitive geometries that are currently built with expensive formwork. If you can print them on site with a mobile gantry, you save time and material. Peri has already done a few noise barrier projects along the A1 autobahn near Dortmund. Luna: Those are perfect candidates — they're long, linear, and don't have complex interior spaces. And they're usually in remote areas where formwork logistics are a headache. Lucas: Exactly. So the factory of the future for construction might not be a central plant at all. It might be a mobile printing rig that moves from site to site, printing walls and barriers and foundations using locally sourced recycled aggregate. Peri is prototyping a containerized version of their gantry that can be trucked and assembled in under a week. Luna: That's fascinating. But what about the quality control? If you're printing on site, you don't have the controlled environment of a factory. Temperature, humidity, wind — all affect the curing of geopolymer concrete. Lucas: That's a real issue. Geopolymer curing is sensitive to temperature — it accelerates in heat and slows in cold. Peri has developed admixtures that extend the working temperature range, but they still recommend printing only between 5 and 35 degrees Celsius. They also use sensors embedded in the print head to monitor the concrete's viscosity and adjust the mix in real time. It's a feedback loop: the printer measures the material properties and tweaks the feed rate or the nozzle pressure accordingly. Luna: So it's not just a 3D printer — it's a smart manufacturing system. That's a different level of complexity than a typical construction site is used to. Lucas: And that's the adoption barrier. Construction is a conservative industry. The workforce is used to pouring concrete into forms, not operating CNC machines. Peri offers training programs, but it's a shift. The early adopters are mostly large contractors who have in-house engineering teams. For smaller builders, there's a learning curve. Luna: Do you think this will ever become the default method for building houses? Or will it remain a niche for complex geometries? Lucas: I think it will become standard for certain building components, but not for whole houses — at least not in the next decade. The sweet spot is the building envelope: the walls, the floors, maybe the roof. Interior finishes, plumbing, electrical — those still need traditional methods. So it's a hybrid future. The printed structure provides the shell, and then conventional trades finish the inside. That's actually how Peri's projects work today. Luna: So we're not looking at a Jetsons-style robot house. We're looking at an optimized concrete shell that saves material and labor on the structural side, and then everything else stays the same. Lucas: Exactly. And that's realistic. The construction industry doesn't change overnight. But if you can reduce the carbon footprint of the structure by 60 percent, and maybe save 10 percent on total project cost for complex buildings, that's a meaningful improvement. It's not a revolution, but it's a real step forward. Luna: And it's happening today in a factory in Beckum. Not in a lab, not in a PowerPoint. Lucas: Right. That's the most important thing. It's easy to get excited about futuristic technology that never scales. But Peri is shipping product. The walls are in the ground. That's the story.