Moon dust and urine make for a strong cement that could help build a colony on the satellite, according to a study published in the Journal of Cleaner Production.
With NASA, the European Space Agency, China, and Russia looking to establish human settlements on the Moon, 3D-printed materials and objects made with the help of in situ resources could help in their endeavour.
In order to set up outposts on other planets or the Moon in a somewhat economical fashion, humans will need to make the most of locally available materials. Shipping resources from the Earth to the Moon, or elsewhere, can be exorbitant. For instance, NASA suggests that each kilogram of material put into orbit around the Earth will incur a cost of approximately $20,000 or around €18,000.
In the past, researchers have proposed the use of lunar soil to make 3D-printed homes for astronauts. But mixing cement uses a lot of water, which is in short supply on the Moon and far too heavy to be transported from Earth.
Another option for habitation would be to drill caves into lunar rock. Researchers across Europe came up with a less-drastic option — urea cement. Combining lunar regolith, which is the loose, upper layer sitting above solid rock, and binding agent such as urea found in urine, the team were able to craft a superior building material. This urea-based cement could help astronauts or even settlers build homes on the Moon.
The Moon lacks an atmosphere, making it particularly vulnerable to strong radiation and meteoric hits. The Earth is hit with around 44,000 kilograms of meteoric material, and the Moon isn’t far behind. The Moon also experiences a wide range of temperatures—from 120 ℃ in the day to −130 ℃ in the night. Any structures built on the Moon must be able to insulate against these varying conditions.
The urea “allows hydrogen bonds to break and therefore reduces the viscosities of many aqueous mixtures.” This means, urea molecules let water-based substances flow more easily, but allows them to harden in the sunlight during a lunar day.
The research team used a substance they named ‘lunacrete’, consisting of silica and aluminum oxide powder to mimic lunar dust, undistilled urea extracted from urine, and some water. They added this mixture to a 3D printer and analysed its suitability as a plasticizer. The “urea worked very well” in comparison to two superplasticizers normally used in construction on Earth, says Professor Anna-Lena Kjoniksen, a chemist at Ostfold University College in Norway and coauthor on the study. The substance that retained its form under light weights and temperature variations, was used to print out a small wall.
In the future, Kjoniksen will subject the lunacrete to radical temperatures and place it in a vacuum system that simulates the Moon’s atmosphere-less surface. The lunar cement will also be used to build larger walls. They also plan on studying if the urine needs to be purified or if it can be used as is in the cement.
Reference: S. Pilehvar et al. Utilization of urea as an accessible superplasticizer on the moon for lunar geopolymer mixtures. Journal of Cleaner Production. Vol. 247, February 20, 2020. doi: 10.1016 / j.jclepro.2019.119177.