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Eggshell Benches, Circularity Park, Oberglatt, Eberhard AG, 2021-2022
The so-called Eggshell fabrication process is a method of producing highly-customized concrete building elements using 3D printed formwork. By using 3D printing to produce the formwork, complex designs can be fabricated efficiently in an automated process. This allows for the fabrication of optimized building components such as columns, beams, and floor slabs. In this project at the Circularity Park in Oberglatt, we are combining 3D printing of a recyclable formwork with casting of a low-carbon concrete, to realize a novel, digital, and sustainable method for producing concrete structures.

Computational design
The design of the benches at the Circularity Park has been created thanks to a computational design script. Thanks to this latter, the design of the benches could be controlled and generated through several curves, meaning that it could still be adjusted until just before fabrication. The same script was also used to create the plans for the benches’ steel reinforcement.

Robotic 3D printing of thin recyclable formwork
An industrial robotic arm 3D prints a thin formwork from a recycled, thermoplastic material. The print has the width of one single extrusion layer and has integrated stiffening ribs that provide the formwork with additional strength during casting. The benches are printed in a vertical position, directly on top of the formwork plate that acts as the base. Each of the bench formworks takes between 5 to 8 hours to be printed.

Casting of low-carbon concrete
The bench formworks are cast with zirkulit®, a concrete in the circular industry with maximum percentage of reused secondary materials and with low carbon emissions. The new mix design of zirkulit® concrete contains a minimum of cement and selected low-carbon cement types. A further reduction of carbon emissions is achieved by a newly developed carbon storage technology of zirkulit AG. Here, the CO2 penetrates the pores of the secondary granules and reacts into limestone. These benches illustrate the combination of the two innovations of low-carbon concrete and 3D printing of formwork.

Sustainability
3D printed formwork allows the production of more efficient concrete structures, as it makes it possible to place concrete exclusively where it is structurally needed. Additionally, it is also possible to print formwork from recycled plastics, a waste product from industrial processes. After casting, the plastic formwork is taken off, and it can be recycled again. The formwork for the robotic benches, for example, was shredded and then reprinted to serve as formwork for a concrete pavilion.

Credits:
Gramazio Kohler Research, ETH Zurich

Client: Eberhard Unternehmungen AG
Collaborators: Joris Burger, Guillaume Jami, Dr. Ena Lloret-Fritschi, Dr. Lauren Vasey
Selected experts: Remo Hug (zirkulit AG), Elia Quadranti, Sandro Kühne (ATP architekten ingenieure), Prof. Dr. David Kammer, Dr. Mohit Pundir, Flavio Lorez (Chair of Computational Mechanics of Building Materials)
Support: Philippe Fleischmann, Michael Lyrenmann, Tobias Hartmann, Andreas Reusser (Robotic Fabrication Lab, ETH Zurich)
Copyright 2022, Gramazio Kohler Research, ETH Zurich, Switzerland
Gramazio Kohler Research
Chair of Architecture and Digital Fabrication
ETH Zürich HIB E 43
Stefano-Franscini Platz 1 / CH-8093 Zurich

+41 44 633 49 06
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