Recycled glass could be renewable solution 3D-printing is waiting for
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Singapore researchers have developed the capability to replace the sand used in 3D-printing with environmentally friendly recycled glass.
Researchers from Nanyang Technological University, Singapore (NTU Singapore) have developed the capability to use recycled glass in 3D-printing, opening doors to a more environmentally sustainable construction industry.
Glass is one material that can be 100 per cent recycled with no reduction in quality, yet it is one of the least recycled waste types.
According to the latest data by the National Environment Agency of Singapore, only 13 per cent of the 74,000 tonnes of glass waste generated in the country was recycled in 2021. Glass is made up of silicon dioxide, or silica, which is a major component of sand and, therefore, it offers significant untapped potential to be recycled into other products.
At the same time, growing populations, urbanisation and infrastructure development have led to a sand shortage, with climate scientists calling it one of the greatest sustainability challenges of the 21st century.
Using recycled glass as a replacement for sand in 3D-printing would be a perfect solution to these challenges.
According to an article published in the Journal of Building Engineering, the NTU team set out to create a concrete mix comprising recycled glass, commercial cement products, water and additives to 3D-print a concrete bench. By figuring out the optimal concrete formulation, the research the researchers were able to successfully 3D-print a 40cm tall L-shaped bench as a proof of concept that their material could be 3D-printed into an everyday structural product.
In lab compression tests and filament quality tests, the bench showed excellent buildability, meaning the printed concrete does not deform or collapse before the concrete cures, and extrudability, which refers to the fact that the concrete mix is fluid enough to flow through the hoses and print nozzle.
While scientists elsewhere have described the use of glass in concrete mixtures, none of them has been able to successfully 3D-print a structure using a glass-based concrete mixture, until now.
Professor Tan Ming Jen, principal investigator of the study from the NTU School of Mechanical and Aerospace Engineering (MAE) said: “Our team has come up with a feasible formula, demonstrating for the first time that glass can indeed be used to 3D-print a bench with excellent structural integrity.
“70 per cent of glass is made up of silicon dioxide, or silica. What our research does is to essentially return the silica found in glass to be reused again as sand in our 3D-printing concrete mixture.”
The NTU research team believes its development offers a new pathway to recycling glass waste and can contribute to a greener building and construction industry for Singapore and beyond.
Prof. Tan and his team at NTU’s Singapore Centre for 3D Printing (SC3DP) were also behind the 3D-printed bathroom project in 2019, where an unfurnished bathroom was printed in 12 hours in Singapore - half the time required for conventional construction of the same facility.
Andrew Ting, a researcher at the SC3DP, said: “Given that sand is being exploited at a rate much quicker than it can be replenished naturally, the prospect of using recycled glass in building and construction is becoming more attractive. We believe our development has great potential to relieve the demand on sand for this sector in the future.”
As the second most widely used substance after water, concrete relies on sand as a vital ingredient to ensure its durability. Reports by the United Nations Environment Programme have revealed aggressive sand extraction from rivers has led to pollution, flooding and other environmental consequences around the world.
Through detailed and extensive analysis and testing, the NTU research team established the optimal parameters for the recycled-glass concrete mixture that would allow it to be 3D-printed.
Components of the mixture include recycled glass crushed to different size classes (medium, fine and superfine), commercial cement product, water and other additives. To enable printing, the team adjusted the control systems of the 3D-printer to match the flow rate of the nozzle to the hardening properties of the concrete.
The printing was then carried out in a single build using a 4-axis gantry robotic printer which has a print volume of 1.2 metre x 1.2 metre x 1 metre. The specially designed concrete mixture was fed to a pump and transported to a nozzle mounted on the robotic arm, depositing the material layer by layer according to the digital blueprint.
Moving forward, the NTU research team, in collaboration with Singapore start-up company Soda Lemon, will look at 3D printing larger scale and more diverse structures using the recycled glass concrete mix, as well as optimising the printing algorithm for consistent performance.
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