Researchers from Nanyang Technological University (NTU) in Singapore have found a way to use recycled glass in 3D-printing. This breakthrough could make the building and construction sector more sustainable.
Less than 15% of the 74 000 tonnes of glass waste generated in Singapore was recycled in 2021 with most of the rest incinerated or landfilled. While glass has been used in concrete mixes, NTU’s research is the first to successfully 3D-print a structure using a glass-based concrete mixture.
The new process uses a specially formulated concrete mix of recycled glass, commercial cement products, water and additives to 3D-print a concrete bench. Using an optimal formulation, the NTU research team made a 40cm tall L-shaped bench as a proof of concept that their material could be printed into an everyday weight-bearing product.
In lab compression and filament quality (strength) tests, the structure showed ‘excellent buildability’, meaning the concrete does not deform or collapse before curing.The mix was fluid enough to flow through the hoses and print nozzle.
‘The main challenge in formulating 3D-printable concrete mixtures is to figure out just how much of each component to add to obtain a structurally sound structure with minimal defects,’ says project lead Professor Tan Ming Jen. ‘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.
‘Around 70% 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.’
As a result of the proof-of-concept, the NTU team believes the development offers a ‘new pathway’ to recycling glass waste and offers a greener building and construction material in line with the circular economy.
The new development builds on previous 3D-printing for construction research. The researchers were able to print the floor and walls of a bathroom in 12 hours, half the time required for conventional construction.
As a next step, the researchers will collaborate with Singapore start-up company Soda Lemon on larger and more diverse structures using the recycled glass concrete mix. They also plan to optimise the printing algorithm for consistent performance.