Living ‘concrete’ made from bacteria used to create replicating bricks

A type of living concrete made from bacteria could one day help to reduce the environmental impact of the construction industry.

Wil Srubar at the University of Colorado Boulder and his colleagues have used a type of bacteria, Synechococcus, to create building blocks in a variety of shapes.

The team combined the bacteria with gelatin, sand and nutrients in a liquid mixture, then placed this in a mould. With heat and sunlight, the bacteria produced calcium carbonate crystals around the sand particles, in a process similar to how seashells form in the ocean.

When cooled, the gelatin solidified the mixture into a gel form. The team then dehydrated the gel to toughen it, with the entire process taking several hours.

The team liken their living material to concrete, which is a mixture of gravel and sand and cement combined with water. But its mechanical properties are more similar to mortar, a weaker material usually made with cement and sand and found between the bricks of buildings, says Srubar. It isn’t yet as strong as regular bricks.

An advantage of using bacteria to create the concrete is that if they aren’t dehydrated entirely, they continue to grow. One brick can be split to create two bricks with some additional sand and nutrient solution. The team showed that one brick could yield up to eight in total after several divisions.

“If you use biology and species of bacteria that grow at exponential rates, you could theoretically move from a linear manufacturing approach to an exponential manufacturing approach,” says Srubar.

The process has the potential to make energy intensive concrete production more environmentally friendly because of its reliance on photosynthesis. “Concrete is the second-most consumed material on earth after water,” says Srubar.

The work was funded by the US Defense Advanced Research Projects Agency (DARPA) and Srubar says the team is now in talks with the US Department of Defense to scale up production of the concrete and pilot its use in construction.

Journal reference: Matter, 10.1016/j.matt.2019.11.016

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