‘Living’ brick can grow itself from CO2

Researchers in the US have developed a recipe for a ‘living’ brick able to grow itself by sucking CO₂ from the atmosphere.

The team at the University of Colorado in Boulder impregnated a ‘scaffold’ of gelatin and sand with bacteria, which with the right light and humidity, grew and hardened to create bricks with the same strength as cementitious mortar.

The microbes photosynthesise and consume carbon dioxide from the atmosphere as they grow and in the right conditions can live for up to a month. This raises the possibility of using them to create more efficient self healing construction materials or to grow bricks in an industrial process.

Environmental performance is boosted by the fact that bricks can be ‘melted down’ after demolition and reconstituted to cut waste associated with demolishing regular brick structures.

Chelsea Heveran, lead author of the study and now assistant professor at Montana State University, told RIBAJ: ‘What is so exciting about this process is that you're building a structure that could later be removed and, unlike cementitious structures, [you could] recycle pretty much the whole thing. You could melt it down and recast it, add more cells and grow it again. Think of the gelatin as a web between the sand and the cells, if you break that into pieces and melt it down, the cells are liberated, and can reproduce.’

The US$1.9 million project was funded by the Defense Advanced Research Projects Agency, an agency of the US Department of Defense, which challenged researchers to develop a material for use in harsh locations that could be made quickly using less human effort.

The cyanobacteria grow in a solution of sand and gelatin and produce calcium carbonate, the main ingredient in limestone and cement. With treatment, this mineralises the gelatin and binds the sand together to form a tough and strong brick.

In certain humidity conditions, between 9% and 14% of the bacterial colonies in the bricks were still alive after 30 days, including three distinct generations, whereas bacteria used in self-healing concrete typically has survival rates of less than 1%.

According to the study, the bricks are self-regenerating. Heveran said: ‘If you wanted to build a new structure and you had just one brick and a humid environment with live cells, you could cut the brick in half, add more of the sand and hydrogel scaffold to one half of it and heat it up. The cells would grow to make more calcium carbonate and create a new brick.’

This technique could underpin a new form of biological manufacturing, using bacteria to fabricate structural materials exponentially at scale, she added: ‘There have been great demonstrations of scaling up microbial based processes across lots of applications. No single component of our system is prohibitively challenging to manufacture.’

The bacterial growth process is halted when the structure dries out, causing the cells to die, so cutting humidity levels could help control the manfacturing process. The team is also working to engineer microbes that are more resistant to drying out and remain alive and functional even in arid conditions.

The study did not include a robust CO₂ lifecycle analysis, however the material’s bond using natural processes and to suck pollution from the atmosphere has significant implications. According to think tank Chatham House, cement production alone is responsible for about 8% of CO₂ emissions worldwide.