Astronauts' urine could be used to improve compounds that could be used to build a space station on the Moon, according to a study sponsored by the European Space Agency (ESA) and published on Friday.
According to the study, urea, the main component of urine, "could make the lunar concrete mixture more malleable before it hardens into the final, strong shape of future lunar habitats," ESA said in a statement.
Added to the geopolymer mix, a concrete-like building material, urine works better than other common plasticisers such as naphthanel or polycarboxylate to reduce the need for water.
Furthermore, when used in a 3D printer, the mixture proved to be stronger and preserved good malleability.
A fresh sample of the composite can be easily moulded and retains its shape, while withstanding weights ten times its own.
"The scientific community is particularly impressed by the high strength of this new recipe compared to other mixtures. They are also attracted by the idea that it allows the use of material already available on the Moon," explains Marlies Arnhof, initiator and co-author of the study from ESA's Advanced Concepts Team (ACT).
At the same time, this mixture would reduce shipments of materials from Earth when building settlements on the Moon, since it would take advantage of elements found on the satellite.
The main ingredient would be lunar regolith, loose rock from the Moon's surface, to which urea would be added as a superplasticiser, limiting the amount of water needed for the recipe.
One person generates approximately 1.5 litres of excremental fluid, making the urine of future Moon inhabitants a "promising product for space exploitation", ESA said.
"Urea is cheap and readily available, and it can be used to make strong construction materials for a lunar base," says Arnhof.
The researchers believe that urea is capable of breaking hydrogen bonds and reducing the viscosity of fluid mixtures, and also contains calcium minerals that aid the setting process.
"On Earth, urea is produced on an industrial scale and is widely used as a fertiliser and as a raw material by chemical and pharmaceutical companies," ESA recalled.
Arnhof expressed confidence that the urine could be used in the construction of a future lunar base, which "would be very practical and would avoid having to further complicate the sophisticated water recycling systems used in space".
Studies show that this type of concrete mixed with urea would be able to withstand adverse space conditions, such as vacuum or extreme temperatures, the factors that most affect the physical and mechanical conditions of construction materials for the lunar surface.
The samples were subjected to vacuum and freeze-thaw cycles to simulate the drastic temperature changes that occur from day to night, ranging from negative 171 degrees to positive 114 degrees.
The study involved researchers from Norway, Spain and Italy in the framework of the Ariadne initiative.
