The urea in astronauts' urine may help erect modules that major space agencies plan to build on the Moon, according to a study which says the chemical could be used as an additive in making concrete for the structures.
According to the researchers, including those from the Polytechnic University of Cartagena (Murcia) in Spain, the colonisation of the Moon poses problems such as high levels of radiation, extreme temperatures, meteorite bombardment, and the logistical issue of getting construction materials to the lunar surface.
They said, currently, transporting about 0.45 kilogrammes of material from the Earth to space costs about USD 10,000, adding that the construction of a complete module on any satellite in this way would be very expensive.
Hence, the scientists said, space agencies are working out ideas to use raw materials from the moon's surface, or even those that astronauts themselves can provide, such as their urine.
The study, published in the Journal of Cleaner Production, assessed the potential of urea in urine as a plasticiser -- an additive that can be incorporated into concrete to soften the mixture and make it more pliable before it hardens.
"To make the geopolymer concrete that will be used on the moon, the idea is to use what is there, regolith (lunar soil) and the water from the ice present in some areas," explains Ramon Pamies, a co-author of the study from Polytechnic University of Cartagena.
"But moreover, with this study we have seen that a waste product, such as the urine of the personnel who occupy the moon bases, could also be used," Pamies said.
Pamies said the two main components of urine are water and urea -- a molecule that allows the hydrogen bonds to be broken and, therefore, reduces the viscosities of many aqueous mixtures.
Using a material developed by the European Space Agency that is similar to moon regolith, along with urea and various plasticisers, the researchers, using a 3D printer to manufacture various 'mud' cylinders and compared the results.
The experiments, according to the researchers, revealed that the samples carrying urea supported heavy weights and remained almost stable in shape.
Once heated to 80 degree Celsius, the resistance of the structures was also tested and increased after eight freeze-thaw cycles like those on the Moon, the study noted.
"We have not yet investigated how the urea would be extracted from the urine, as we are assessing whether this would really be necessary, because perhaps its other components could also be used to form the geopolymer concrete," said another co-author of the study from the Norwegian university, Anna-Lena Kjoniksen.
"The actual water in the urine could be used for the mixture, together with that which can be obtained on the Moon, or a combination of both," Kjoniksen added.
According to the study, further testing is needed to find the best building material for the moon bases, where it can be mass-produced using 3D printers.