Fixing cracks in space bricks with bacteria

Researchers at the Indian Institute of Science (IISc) have developed a bacteria-based technique to repair bricks that can be used to build lunar habitats, if they get damaged in the moon’s harsh environment.

Future lunar expeditions are no longer planned as just flyby missions. NASA’s Artemis programme, for example, seeks to set up a permanent habitat on the moon. To cut costs, instead of carrying material from Earth, astronauts would need to use the abundantly available lunar soil or “regolith” – a complex mixture of broken minerals and rocks – to build structures on site.

A few years ago, researchers at the Department of Mechanical Engineering (ME), IISc developed a technique that uses a soil bacterium called Sporosarcina pasteurii to build bricks out of lunar and Martian soil simulants. The bacterium converts urea and calcium into calcium carbonate crystals that, along with guar gum, glue the soil particles together to create brick-like materials. This process is an eco-friendly and low-cost alternative to using cement.

Subsequently, the team also explored sintering – heating a compacted mixture of soil simulant and a polymer called polyvinyl alcohol to very high temperatures – to create much stronger bricks. “It’s one of the classical ways of making bricks,” explains Aloke Kumar, Associate Professor at ME and corresponding author of the study. “It makes bricks of very high strength, more than adequate even for regular housing.” Sintering is an easily scalable process – multiple bricks can be made at once in a furnace.

But the lunar surface is extremely harsh – temperatures can swing from 121°C to -133°C in a single day and it is constantly bombarded by solar winds and meteorites. This can cause cracks in these bricks, weakening structures built using them. “Temperature changes can be much more dramatic on the lunar surface, which can, over a period of time, have a significant effect,” explains co-author Koushik Viswanathan, Associate Professor at ME. “Sintered bricks are brittle. If you have a crack and it grows, the entire structure can quickly fall apart.”

To solve this problem, the team once again turned to bacteria. In a new study, they created different types of artificial defects in sintered bricks and poured a slurry made from S. pasteurii, guar gum, and lunar soil simulant into them. Over a few days, the slurry penetrated into the defects and the bacterium produced calcium carbonate, which filled them up. The bacterium also produced biopolymers which acted as adhesives that strongly bound the soil particles together with the residual brick structure, thereby recovering much of the brick’s lost strength. This process can stave off the need to replace damaged bricks with new ones, extending the lifespan of built structures.

“We were initially not sure if the bacteria would bind to the sintered brick,” says Kumar. “But we found that the bacteria can not only solidify the slurry but also adhere well to this other mass.” The reinforced bricks were also able to withstand temperatures ranging from 100°C to 175°C.

“One of the big questions is about the behaviour of these bacteria in extraterrestrial conditions,” says Kumar. “Will their nature change? Will they stop doing [the carbonate production]? Those things are still unknown.”

The team is currently working on a proposal to dispatch a sample of S. pasteurii into space as part of the Gaganyaan mission, to test their growth and behaviour under microgravity. Viswanathan says: “If that happens, to our knowledge, it will be the first experiment of its kind with this type of bacteria.”