A team of scientists from the University of Tartu and the Estonian University of Life Sciences have developed a new construction 3D printing material which has the potential to drastically decrease construction costs for private homes. The material, made from milled peat and oil shale ash, is not only low cost but could pose environmental benefits as well.
Peat, a natural material made from decomposing vegetation that forms in bogs and other wetland environments, is one of the most efficient carbon sinks on the planet, meaning that it stores carbon compounds. Because of this, peat has been used as an important source of fuel in certain parts of the world for over a century.
In Estonia, where wetlands cover about 22% of the land, peat is in abundance. Unfortunately, much of it has been deemed unsuitable for use—only the drier top layer of peat is typically harvested—leaving much of it unexploited.
In their development of a self-supporting construction material that used local natural resources, the Tartu scientists realized that they could perhaps leverage Estonia’s peat abundance. “So far, no one has produced peat composite as a construction material because peat prevents many materials from hardening,” said Jüri Liiv. “In our project, we managed to overcome this issue.”
The solution for using peat as a 3D printing construction material, as it turns out, was to add oil shale ash as the binder material. The material, a byproduct of oil shale, is typically seen as a hazardous waste product, though in recent years its construction viability has increasingly been explored.
As the researchers explain, the material becomes very basic when it comes into contact with water, making it hazardous in most cases. For construction materials, however, oil shale ash’s pH is beneficial and the material can be used in a safe, environmental way. In Estonia alone, over 7 million tonnes of oil shale ash are created every year, and typically only 5% of the byproduct is reused (with the rest ending up in ash hills).
The addition of oil shale ash to the peat mixture has enabled the scientists to reduce the setting time for the construction material from 30 days to a single day. This, they explain in more detail, is because if the pH of a pore solution is below 9 it won’t harden at all, but if it can be increased by binding the potassium oxide and alkali metals from oil shale ash, it can harden much faster.
The oil shale ash itself reacts with the humic acids inside the peat material and absorbs carbon dioxide, resulting in a binder that “becomes regular concrete and limestone.” To improve the construction material’s properties further, the scientists have also added nanosized additives (such as nanosilica or silicon smoke).
“As the particles are very small, they dissolve well and distribute throughout the material evenly. Silicon smoke improves the quality of this material significantly,” said Toomas Tenno, a professor at the University of Tartu’s chair of colloidal and environmental chemistry.
The resulting peat material developed by the scientists, which took about a year to achieve, is a strong construction material with lightweight properties and good thermal conductivity. Importantly, the material is highly durable and (despite the fact that peat is used as fuel) is incombustible, making it safe for building applications.
The scientists add that the material becomes hard within 24 hours but retains elasticity for longer. The material is also airtight, removing the necessity for insulation or fillers, and boasts good noise insulation.
Importantly, the 3D printing construction material is inexpensive thanks to the low costs of both peat and oil shale ash. Liiv estimates that the cost for a 100-150 square meter house shell printed from the material would only cost about €5,000 to manufacture—ten times less than traditional construction processes.
Ultimately, the Tartu researchers are aiming to 3D print houses on-site that are up to two-storeys high using the peat material. At this point, though the peat material itself if ready for production, there is still much work to be done on the 3D printing front to be able to properly process it.