Sep 4, 2017 | By Benedict

Researchers from Nanyang Technological University (NTU) in Singapore have used fly ash, a residue from burnt coal, to create a 3D printable geopolymer mortar. The mixture also contains steel slag and various secret chemicals.

Burning coal might not be the most planet-friendly way of generating power and heat, but many places around the world are still completely reliant on the carbonized plant matter. So why not try to take advantage of burning coal in every way possible?

NTU researchers are trying to do just that—by turning a form of coal residue called fly ash into a 3D printable building material.

After conducting research over the course of two years, a team led by Ming Jen Tan (of the School of Mechanical and Aerospace Engineering) recently published its findings in the journal Cleaner Production and Materials Letters.

Innumerable quantities of coal are burned every day, as countries like China continue to press ahead with the power-generating technique over other, greener alternatives like nuclear and wind. This means that huge amounts of by-products are created, most of which have to be disposed of in landfills or via other means.

But the NTU researchers saw an amazing opportunity in fly ash, the last bits that are left after burning coal.

By mixing fly ash with steel slag and a mix of chemicals, the researchers have been able to create a 3D printable geopolymer mortar that can be used to fabricate large, solid structures with concrete 3D printing equipment. They think it could be the future of 3D printed buildings.

Of course, getting everything perfect—from flow rate to setting times—has been a massive challenge, but the NTU team thinks it has come up with a more-or-less viable product, which is incredible given that it comes from waste.

The research team gathered their fly ash from a coal power plant in India, but they say the residue could be collected from other places too: local waste-to-energy plants, for example.

The researchers are also looking at implementing their findings closer to home. Singapore, where NTU is based, has just one landfill, in Pulau Semakau, which will need to be closed up by 2035. But by using waste to make fly ash for this new 3D printing material, the researchers say that date could be postponed, delaying the need for a second landfill.

Perhaps more importantly, the 3D printable concrete would also help the construction industry to reduce its carbon footprint, since no materials need to be made from scratch. Concrete production currently accounts for around five per cent of the world’s carbon dioxide emissions.

The big question, however, is whether this recycled concrete mix performs as well as regular concrete.

According to the researchers’ tests, the 3D printable mixture is just as strong, but only when the structures are oriented in a practical way. This is because the “mechanical properties of [the] 3D printed geopolymer are mostly dependent of loading directions due to anisotropic nature of the printing process.”

Impressively, the researchers think they think they can make the material even stronger—as strong as reinforced concrete. While they don’t know exactly how they will achieve this, the researchers are continuing their study to see if they can perfect their product, while attempting to reduce its cost at the same time.

In the published study, the researchers also discuss how to overcome problems like overhangs. One option, they say, is support structures, while a more quick-setting geopolymer mix could also reduce the need for supports.

Fortunately, the team won’t be short of resources. Last year, NTU pumped $30.7 million into a new 3D printing center, with concrete 3D printing one of its key focus areas.

The study, “Additive manufacturing of geopolymer for sustainable built environment,” can be read here. Its authors were Biranchi Panda, Suvash Chandra Paul, Lim Jian Hui, Yi Wei Daniel Tay, and Ming Jen Tan.

Posted in 3D Printing Materials

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