Jul 11, 2018 | By Thomas

Scientists from the University of Tartu and the Estonian University of Life Sciences have created a construction material from peat and oil shale ash that could reduce the construction costs of a private house nearly tenfold. The aim was to create a self-supporting construction material based on local natural resources and waste that could be used to 3D print houses up to two-storeys high directly at the construction site.

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 printed. Photo above: Toomas Tenno is showing these test pieces. Credit: Merilyn Merisalu

According to the Estonian Wetland Society, wetlands cover about 22 per cent of Estonia's area, but only a third of peat growing there is being used as peat deposits. Another thing that Estonia has a lot of is oil shale ash – the country produces an estimated 7 million tonnes (7.7 million tons) of oil shale ash annually, only 5 percent of which is reused.

"So far, no one has produced peat composite as a construction material because peat prevents many materials from hardening. In our project, we managed to overcome this issue," said Juri Liiv, from University of Tartu.

Oil shale ash is classified as a hazardous waste because it becomes very basic when in contact with water (pH almost 13). However, ash with such a pH is the best fit for construction materials. The developed material is completely harmless and safe for the environment.

Scientists from Tartu have developed a 3D printable concrete-like material made mainly from milled peat, with oil shale ash serving as a binder.

During testing, scientists found a solution for reducing the setting time from about 30 days to one day. If the pH of a pore solution is below nine, it won't harden. This issue is solved by a very high pH by binding the potassium oxide and alkali metals found in oil shale ash to insoluble compounds. Inside the peat, oil shale ash reacts with humic acids and absorbs carbon dioxide. Due to chemical reactions, the binder becomes regular concrete and limestone. In addition, nanosized additives, such as nanosilica or silicon smoke, are added to peat and oil shale ash to improve their properties.

"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.

It took about a year before the right mixture was found for the material that is strong and has high thermal conductivity. After final hardening, the material is strong, light, durable and exhibits a low rate of heat transfer. It is also incombustible despite the fact that peat is also used as fuel. Peat was used as filler to achieve excellent thermal properties - the developed peat material achieves its initial hardness in 24 hours but remains elastic for some time after. The entire structure becomes airtight without adding any wind protection, and it is also good at blocking sound.

As peat and oil shale ash are very cheap, scientists calculated that 3D printing a house shell (100-150 square meters) with it would cost about €5,000, around one-tenth what it would cost to construct a traditional framed shell of the same size.

The team is now working on a way to make the material easier to print. A paper on the research was recently published in the journal Sustainable Materials and Technologies.



Posted in 3D Printing Application



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