[Image above] Researchers from Nanyang Technological University, Singapore showed a glass-containing concrete mix can be used to 3D print various structures. Credit: NTU Singapore
By Laurel Sheppard
Though three-dimensional (3D) printing has existed in concept and primitive practice for decades, it is only during the past 10 years that this group of manufacturing techniques solidified its position as a mature technology.
In general, 3D printing involves taking a 3D digital model, created by computer-aided design or a 3D scanner, and using it to fabricate an object layer by layer until the final part is complete. There are various techniques that are classified as 3D printing, including established methods, such as stereolithography, and newer methods, such as those developed for 3D printing glass.
Initially, 3D printing methods were only used to fabricate prototypes, but its application has expanded to low-volume production parts as well. Now, the global market for 3D printing is worth billions of dollars and is projected to have double-digit growth, according to market analysts.
The aerospace and automotive sectors are two major industries taking advantage of 3D printing to produce various parts made from a variety of materials. Now, the construction industry is jumping on board the 3D-printing trend.
Potential advantages of building houses or other buildings via 3D printing methods include
- Faster, affordable construction. A project can take mere days or hours instead of weeks or months, lowering overall costs.
- Reduced waste. Components are printed to order, producing less waste. Any unused materials can generally be recycled. Sustainability of the build is further improved by using locally sourced materials.
- Reduced health and safety risks. Conventional concrete work is often hazardous. 3D printing lowers the risks considerably, reducing worker’s compensation costs.
For these reasons, many construction companies are interested in the potential of 3D printing to address the affordable housing crisis. For example, companies have constructed 3D-printed homes in Mexico, Italy, and the United States, among other places, with the latter development claiming to be the world’s largest community of 3D-printed homes.
For 3D-printed buildings, concrete is often the material of choice. While traditionally this concrete consists of sand, gravel, and cement mixed with water, with sand in increasingly short supply, another material may be needed.
Researchers from Nanyang Technological University (NTU), Singapore came up with a potential solution: replacing sand and gravel with glass waste that would otherwise end up in landfills.
Even though glass is infinitely recyclable without loss in quality, we often fail to make use of its potential—less than a third of glass containers was recycled in 2018, according to the U.S. Environmental Protection Agency. So, many researchers are exploring ways to increase glass recycling and reuse rates, such as by including it in concrete.
For their study, the NTU researchers first crushed post-consumer glass waste into three different sizes using a vertical shaft impactor:
- Medium (1,000–1,700 μm)
- Fine (500–1,000 μm)
- Superfine (150–710 μm).
After combining the ground glass with cement and water, they extruded the mixture through the nozzle of a 4-axis gantry robotic 3D printer to create a 40-cm tall (15.8-in.) L-shaped concrete bench. Once the concrete cured, it was similar in mechanical strength to traditional sand-containing concrete, meeting industry standards.
Extrudability depended on the glass aggregates/binder ratio, nanoclay content, and fineness modulus. The extrudable limit values for these three properties were determined at 0.9, 0.2%, and 2.4, respectively. Staying in these limits allowed the fluid cement to flow easily through the printer nozzle and prevented the poured concrete from deforming or collapsing before it cured. The researchers also found that
- Deformation increases linearly with an increase in compressive load at a constant rate.
- Increasing the nanoclay content and glass aggregates/binder ratio, and decreasing the glass aggregate fineness modulus, decreases filament deformation up to the extrudable limits.
- Compressive strength also depends on the glass aggregates/binder ratio, nanoclay content, and fineness modulus parameters.
Another major benefit of this concrete is it requires less water because glass does not absorb as much water as sand.
In an NTU press release, Andrew Ting, first author and researcher at the Singapore Center for 3D Printing, says, “Our research has shown that recycled glass can be used to replace up to 100% of the sand in concrete for 3D printing. … We believe our development has great potential to relieve the demand on sand for this sector in the future.”
The NTU researchers now plan to collaborate with Singapore start-up company Soda Lemon to look at 3D printing larger scale and more diverse structures using the glass-containing concrete mix, and to optimize the printing algorithm for consistent performance.
The paper, published in Journal of Building Engineering, is “Extrudable region parametrical study of 3D printable concrete using recycled glass concrete” (DOI: 10.1016/j.jobe.2022.104091)