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Artist’s impression of five 3D printed concrete houses that will be built in Eindhoven. [Image: Houben/Van Mierlo Architects]

By using 3D printing to fabricate structures ranging from hotels and houses to bridges and bus stops, the global construction industry is able to lower costs and increase production speeds, along with making improved, eco-friendly structures with better designs and building materials.

The most commonly used materials for 3D printing structures are concrete and cement. However, there has been research on more unique materials like cellulose, a mixture of seeds and clay, and even materials like bone, skin, bark, and coral for living structures that can fix themselves. Now, scientists from the University of Tartu in Estonia and the Estonian University of Life Sciences have developed a novel new construction material that’s made primarily from peat.

Peat is a soft, heterogeneous mixture of mostly decomposed plant material that’s accumulated in water-saturated environments, like wetlands, in the absence of oxygen. The Estonian Peat Association says that peatlands cover roughly 3% of the Earth’s land area, and peat is also a good alternative to imported fossil energy. You can even mine it through a milling process, where 10 to 20 mm layers are cut loose from the deposit and left to dry; however, most fields need to be larger than 100 hectares for this to pay off.

Peatlands [Image: Estonian Peat Association]

22% of Estonia’s land area is covered in wetlands, which are ripe for growing peat. But, only the drier top part of the peat layer in these areas has been deemed suitable for use, while the unused portions are left to decay. These portions could still be used to help save money – many fractions, like waxes and humic substances, can be separated out from the peat, and you can even produce cellulose with the final residue.

That’s why Estonian researchers have created a self-supporting 3D printing construction material made up of peat and oil shale ash that could lower the costs for a two-story house 3D printed on-site by nearly tenfold.

“So far, no one has produced peat composite as a construction material because peat prevents many materials from hardening,” said Jüri Liiv, a doctor of chemistry at the University of Tartu. “In our project, we managed to overcome this issue.”

Liiv created an organic humate bedding powder out of peat, poultry manure, and wood ash a couple years ago, and while testing which pellets had suitable hardness, he started wondering if peat could be used to create a self-sustaining building material. The answer was yes, and the scientists got right to work.

Instead of using cement, Tartu researchers chose oil shale ash as their mixture’s binder. Because it becomes very basic when it comes into contact with water, this material is classified as a hazardous waste, with a pH of nearly 13. But, ash with such high pH levels is the best for construction materials, and once developed, it’s environmentally harmless.

About 7 million metric tons of oil shale ash are created each year in Estonia, but only 5% is reused – the rest causes major environmental pollution once it’s deposited in ash hills. During tests, scientists discovered a way to reduce the setting time for the peat down to one day from 30 – the material won’t harden if the pH of the pore solution is below nine, so they bind the potassium oxide and alkali metals found in oil shale ash to insoluble compounds to create a very high pH.

Oil shale ash reacts with humic acid while inside the peat, and absorbs carbon dioxide. Then, this binder material succumbs to chemical reactions and turns into regular concrete and limestone. Toomas Tenno, a professor of colloidal and environmental chemistry at Tartu, said that nanosized additives, like nanosilica or silicon smoke, are also added to the peat and oil shale ash to improve their properties.

After determining the humic and fulvic acid content in peat and conducting the XRD analysis of elements and minerals, the possible test mixtures were modeled and small test pieces 3D printed. Here, Toomas Tenno is showing these test pieces. [Image: Merilyn Merisalu]

“As the particles are very small, they dissolve well and distribute throughout the material evenly,” explained Tenno. “Silicon smoke improves the quality of this material significantly.”

It took the team a year to find the optimal mixture that’s strong, with high thermal conductivity. Once it’s hardened, the material is lightweight and durable, with low heat transfer, and is incombustible – even though peat can be used as fuel. While the material takes a day to achieve its initial hardness, it stays elastic for much longer, so you don’t need any fillers or insulation, and structures 3D printed with the peat material become airtight, and noise-blocking, without adding any type of wind protection.

Plenty of research and tests have been completed on this new material, and it’s ready to be manufactured for smaller elements. Additionally, Liiv said the scientists calculated that it would only cost about €5,000 to 3D print the shell of a 100-150 square meter house with this new material, due to the face that peat and oil shale are inexpensive; it would cost ten times more to construct the shell of a framed building of the same size. But while the cost savings alone may make you want to start milling peat for your own 3D printed home, the scientists say that the material isn’t quite ready for 3D printing just yet.

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.

[Sources: Phys.org / University of Tartu]

 

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