A golden resource for space travel? The building material of the planned stations on the lunar surface could contain an ingredient that is continuously produced by the colonists themselves – urine. Researchers were able to show that the urea contained in it is suitable as a plasticizer in the production of concrete from lunar material. The mixture can thus be used to manufacture components using 3D printers, the scientists explain.
The step to the moon was made more than 50 years ago – now people will soon be able to gain a permanent foothold there: NASA, the European Space Agency (ESA) and their Chinese counterpart are planning to build moon bases in the coming decades. Later, more distant targets are also in the sights of space travel: One day, humans could colonize Mars, according to the vision of the future.
However, enormous challenges have to be mastered in the implementation of the plans: Settlements on the moon must be able to withstand the extreme temperature fluctuations, meteorite shelling and the intense radiation. So very robust building material is required. However, as little of this as possible should come from Earth. Because the transportation of about 0.45 kilograms of cargo into space costs about 10,000 dollars with existing rocket technology. The construction of a moon base with earthly material would be extremely expensive and logistically difficult to implement.
Even moon colonists have to go to little astronauts
For this reason, the space authorities want to make the best possible use of the moon’s resources and also the substances that are inevitably generated there as part of the manned missions. In this context, the potential of astronaut urine has been successfully used several times in space. Among other things, the substance can be used for the production of drinking water or for the fertilization of space vegetables. An international team of researchers is now presenting another possible use for this golden resource of space travel.
As part of their study, the scientists examined the extent to which the urea contained in the urine is suitable as a plasticizer for the production of concrete on the moon. As they explain, the geopolymer building material could be made from the loose material of the lunar surface – the so-called regolith – and the water that comes from the known ice deposits of the celestial body. The scientists report that special 3D printers could be used to give the moon concrete certain shapes before it hardened.
Plasticizer for 3D printed moon concrete
To do this, however, the starting mixture must be smooth – a plasticizer is therefore necessary. For this reason, the urine came into focus. “The two main components of this body fluid are water and urea. It is a molecule that can break hydrogen bonds and thus reduce the toughness of many aqueous mixtures, ”explains co-author Ramón Pamies from the Polytechnic University of Cartagena.
The researchers tested whether urea can fulfill this function in the manufacture of lunar concrete using a material developed by ESA that resembles the lunar regolith. In addition to urea, various plasticizers were used as additives, which are already used technically for the production of geopolymers. Material without the addition of a plasticizer was used as a control. Using a special 3D printer, the researchers made cylinders from all the test materials, which they then examined.
As they report, the addition of about three percent urea had a similarly favorable effect on the concrete material as the use of the other plasticizers. The tests showed that the printer could not produce well-structured cylinders without the additives. After hardening, the control structures also proved to be less resilient. The urea-concrete cylinder, on the other hand, was similarly stable as the other comparison objects. The material was also resistant to repeated frost-thaw cycles, as can be expected on the moon. “Overall, urea has promising properties as a plasticizer for 3D printing of lunar geopolymers,” the scientists write.
The researchers now want to further explore the substance’s potential. “It may not even be necessary to extract the urea from the urine. Because maybe its other main ingredient could also be used to make the geopolymer concrete, ”says co-author Anna-Lena Kjøniksen from the Norwegian Østfold University College in Halden. “The urine fluid could be used for the mixture, along with the water that can be obtained on the moon.”
In addition, the scientists now want to test what effects vacuum conditions have on the 3D printing of urine-moon concrete and how powerful the material is: They want to investigate, for example, the extent to which meteorite strikes resist it or the colonists from the radiation in space can protect.
Source: FECYT – Spanish Foundation for Science and Technology, professional article: Journal of Cleaner Production, doi: 10.1016 / j.jclepro.2019.119177