ADDITIVE MANUFACTURING
CUTTING CARBON T
How 3D printing is revolutionising construction by reducing material use and carbon emissions for a more sustainable and resilient future
raditionally conservative, the construction sector must now demonstrate innovation given the climate emergency
in order to improve the sustainability of the built environment. To achieve carbon neutrality, conventional construction methods must be transformed through innovative techniques including automation and robotics. 3D printing of concrete is an emerging technology with an immense potential to address sustainability challenges in the modern construction sector with carbon footprint reduction through design optimisation and use of low- carbon inks, as well as enhanced circularity and service life.
BUILDING BETTER WITH LESS 3D printing technology in construction offers a unique ability to minimise material use and create complex geometries that are difficult or impossible to achieve with traditional methods. The ability to print components with these geometries and properties tailored to specific load requirements enhances the overall performance of the structure while minimising material use. This approach ensures that the material is used only where it is needed, reducing both weight and embodied carbon. One such design innovation was
used in the Striatus, a pioneering example of 3D printed infrastructure. Unveiled at the Venice Biennale of Architecture in 2021, Striatus was the first 3D printed masonry bridge, in partnership between ETH Zürich – Block Research Group, Zaha Hadid Architects, Incremental3D and Holcim. In this prototype, the funicular block shapes naturally follow the paths of compressive forces and thus require less material to
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www.engineerlive.com The Pheonix bridge is designed with a specially-developed ink for carbon reduction
achieve the same structural integrity. As these vault structures are purely under compression, the use of steel reinforcement is not necessary. Additionally, the modular nature
of 3D printed components facilitates easier disassembly and recycling at the end of their lifecycle. This modularity means that parts of a structure can be upgraded without the need for extensive demolition, and no sorting of parts as the rebars have been removed from the project, further reducing waste and associated emissions. The lessons from this project provided Holcim with enough insights to launch a second iteration, the Phoenix bridge. Built in 2023 at the Innovation Centre in Lyon, France, the new bridge applies the same structural principles, combining them with specially-developed ink that aims for even further embodied carbon reduction through the application of circular design principles.
SPECIALLY TAILORED INKS The concrete ink used for Phoenix has been specially tailored to its application, while also minimising its carbon footprint. Structural tests used to validate the material performance of Striatus revealed that the new bridge required ink strength of ‘only’ 50 MPa instead of the earlier 90 MPa. Avoiding the trap of over-design helped Holcim save materials but also lowered the carbon footprint of the construction project. These low carbon concrete inks can also incorporate fly ash, slag, or ground granulated blast furnace slag (GGBS), which not only divert waste from landfills but also reduce the need for energy- intensive Portland cement. They may also include construction demolition waste and recycled aggregates for circular projects. In the case of the Phoenix bridge, the TectorPrint ink was composed of 40% of recycled
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