Living concrete made of bacteria and sand

Researchers of University of Colorado Boulder in the US are working on a way to revolutionise building materials, by combining sand and bacteria to build a living material that has structural load-bearing and biological function.

After water, concrete is the most consumed material, but it is also responsible for 6 per cent of global CO2 emissions.

To find a more sustainable alternative, the Colorado researchers created a scaffold out of sand and hydrogel for the bacteria to grow in. The hydrogel retains moisture and nutrients for the bacteria to proliferate and mineralise, a process similar to the formation of seashells in the ocean. Combining the three, the researchers created a green living material that demonstrates similar strength to cement-based mortar.

The hydrogel-sand brick is alive and it also reproduces. By splitting the brick in half, the bacteria can grow into two complete bricks by adding some sand, hydrogel and nutrients. One ‘parent brick’ can reproduce up to eight bricks in three generations. As a bonus, the bricks remove carbon dioxide from the air, rather than emitting it.

For the bricks to be a viable alternative to concrete, they need to be completely dried out, to attain maximum strength. However, the drying process stresses the bacteria and compromises its viability. Therefore, a delicate balance between relative humidity and storage conditions is crucial.

The next step is to explore the numerous applications that the material platform brings. By introducing bacteria with different functionalities, new materials with biological functions could be designed, such as ones that sense and respond to toxins in the air, or building structures on places where there are limited resources, like the desert of another planet.

Photos: College of Engineering and Applied Science at Colorado University Boulder (via EurekAlert)