Green light for digitally manufactured concrete staircase

February 2023

The next unit in NEST, the research and innovation building of Empa and Eawag, is called "STEP2". For around two years, partners from research and industry have been working on various innovations in the areas of circular economy, digital and industrial fabrication, building envelope and energy systems, turning them into products ready for construction. One of them has now reached an important milestone: a globally unique staircase, which is manufactured using 3D-printed formwork and prestressed with an innovation from Empa spin-off "re-fer", has passed the final prototype tests.

It is one of the big challenges in the upcoming NEST unit “STEP2”: a concrete staircase whose shape is reminiscent of a human spine. Although the unit is still in the planning stage, parts of the stairs have already been produced as prototypes. Because the unit pursues a great goal: only what has a future in the construction industry will be built. Together, the partners work consistently towards market readiness – and this is also the case with the staircase.

“Over the past two years, the project team has jointly developed a completely new concept for the production of customised concrete components. This was only possible because the experts along the entire value chain worked together at eye level,” says Enrico Marchesi, innovation manager at NEST and project manager of “STEP2”, with conviction. The interdisciplinary project team was put together together together with the scouting and incubation experts of the main partner BASF. It is made up of the architectural firm ROK, which is responsible for the project management, the ETH Chair of Digital Building Technologies, 3D printing experts from the BASF subsidiary BASF Forward AM and the 3D printing company New Digital Craft, experts from the precast concrete manufacturer SW Umwelttechnik, engineers from the engineering firm WaltGalmarini and the experts from the Empa spin-off “re-fer”.

Customised solutions
The “STEP2” staircase impressively demonstrates how concrete structures can be realised with the help of computer-aided design and the latest 3D printing technologies. By using 3D-printed formwork, it is possible to create more complex shapes than with previous special formwork. At the same time, the amount of material required can be significantly reduced.

The process enables customised concrete solutions that can be optimally adapted to the respective application and have a high level of detail. In addition, it also holds great potential in restoration, for example in the renovation of historical buildings.

High complexity
The design of the staircase comes from the ETH Chair of Digital Building Technologies. Based on this, the project team developed a complex, parameter-based formwork system for the individual steps, which is produced using 3D printing. “It was important for us to use digital fabrication in such a way that we can produce extremely filigree concrete elements. A key criterion for the system was the reusability of the formwork for the production of multiple steps. At the same time, we had to take into account the requirements of 3D printing and the material, as well as the conditions when filling the formwork,” explains Benjamin Dillenburger, head of the “Digital Building Technologies” team. In order to meet all these requirements, the exchange within the entire project team was of central importance.

“In order for the 3D-printed formwork to be used for several stages, we used a suitable coating. In terms of sustainability, we opted for a material that can be detached from the formwork again. This is the only way we can ensure that the material is separated by type,” says Jörg Petri from “New Digital Craft”. He and the “Virtual Engineering” team from “BASF Forward AM” brought their years of know-how in the 3D printing field to the project.

“For BASF Forward AM, the project is an important milestone in demonstrating that the materials used can withstand the high demands. It pays into our strategy to realise formwork using 3D printing as an alternative to conventional mould making,” says Anke Johannes, Director Sales Europe at BASF Forward AM. For the formwork material, the team chose Ultrafuse® PET CF15 filament because of its excellent properties for concrete formwork applications. In the end, the concept for manufacturing and assembling the formwork elements was ready.

The endurance test
Now the time had come to turn the stairs into reality. SW Umwelttechnik produced the steps in its own factory with the help of the formwork. Ultra-high-strength fibre-reinforced concrete was used as the material. “Our concrete allows for very thin, complex shapes that could not be realised with normal reinforced concrete. It’s great that we can demonstrate this so impressively with the staircase in the “STEP2″ unit,” says a pleased Klaus Einfalt, CEO of SW Umwelttechnik.

The WaltGalmarini engineering office is responsible for calculating and assessing the statics. To check whether the calculated values correspond to reality, the steps were sent to Empa. There they were subjected to various load tests by Empa experts under the supervision of the engineering office. The first prototype consisting of three stages, which were all tested individually, largely fulfilled expectations and at the same time provided new findings for optimising the system.

In the subsequent prototype, not only the statics but also the construction of the staircase system was put to the test. Three steps were threaded on top of each other and clamped together using “memory-steel”, an innovative prestressing technique developed by Empa spin-off “re-fer”. In the process, bars of the type “re-bar R18” were placed in predefined cavities and mechanically anchored. The pre-stressing was done by heating with electricity. Afterwards, further tests were carried out to analyse how loadable the steps are individually and the system as a whole. The result: the engineers deemed the overall system reliable.

“I am very pleased that the staircase could not only convince on paper, but now also in practice. This represents an extremely important milestone in the project for us,” says Michael Knauss from ROK. With this “proof of concept”, the production of the final staircase can now take place – another important step towards the realisation of the NEST unit “STEP2”.

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