Published this week in the Journal of Cleaner Production is research that suggests that space agencies like NASA, the European Space Agency (ESA) and the China National Space Administration (CNSA) could utilise the urea in the pee of astronauts as a plasticizer to create “moon concrete” for building structures and modules of their planned moon bases. By combining simulated lunar soil with water and urea, the researchers made 3D-printed geopolymer cylinders that outperformed versions that didn’t include a plasticizer. The researchers also compared their urea-based samples to versions made with more common, polycarboxylate- and naphthalene-based plasticizers. The team found the urea versions could support heavy weights, largely maintain their shape, and withstand eight freeze-thaw cycles (like those lunar bases would experience) about as well as the versions made with the standard plasticizers. “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,” Ramón Pamies, a professor at the Polytechnic University of Cartagena, Murcia, and one of the authors of the new study, says in a statement. In order to make the concrete, the urine would be mixed with lunar regolith, the layer of rocky material that covers the Moon’s bedrock. The urea in the urine is capable of breaking hydrogen bonds, and can therefore reduce the viscosity of the regolith mixture, making it more moldable before it hardens into its final form, according to the study. As a result, the use of urine would reduce the need to find other resources on the Moon such as water, or the need to carry other resources from Earth to the Moon.It costs around $10,000 to transport just about 0.45 kilograms of supplies from Earth to space, therefore transporting entire construction material would be less than ideal. In order to test out this new method, the team of scientists used a material similar to lunar regolith, and mixed it it with urea to create different concrete cylinders using a 3D printer. “To make the geopolymer concrete that will be used on the Moon, the idea is to use what is there: regolith (loose material from the Moon’s surface) and the water from the ice present in some areas,” Ramón Pamies, an engineering professor at the Polytechnic University of Cartagena in Spain and co-author of the study, said in a press release. This geopolymer concrete would then be printed layer by layer to encase a crewed habitat, ideally providing protection from lunar hazards like temperature swings, harmful radiation, and micrometeorites. “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. “The two main components of this body fluid are water and urea.” Perfecting this practice, known as In-Situ Resource Utilization (ISRU), is expected to play a vital role in the future human exploration of the Moon, Mars, and beyond. And though the idea of using urine for construction might be unique, the idea of using lunar regolith is not.