Can bacteria be the solution to collapsing bridges and cracking roads? Researches from Delft Technical University are developing a bacteria-infused concrete that can repair itself.
Concrete is created from a combination of water, aggregate (such as sand, gravel, stone) and cement. It dates back to the Roman Empire and structures made from concrete such as the Pantheon and the Colosseum still stand today. However, concrete tends to form cracks, which reduces its lifetime. Once cracks form, water and chemicals can seep in further reducing its structural integrity. Traditional methods to repair concrete can be costly and require hands-on work. What if there was a way for concrete to heal itself?
This is where bacteria come into play. Concrete-healing bacteria are not just any kind of bacteria; the bacteria that heal concrete must be resilient to arid conditions and must be able to remain dormant for years. Henk Jonkers and Eric Schlangen from Delft Technical University selected a species from the Bacillus genus for their work. Bacillus species are well-studied spore formers that can lie dormant in undesired conditions. If concrete cracks and rainwater seeps in, the water will activate Bacillus cells at the cracks, morphing them from inactive spores to vegetative cells.
Fixing concrete is more than just reactivating bacterial cells to grow; they have to make more concrete! These Bacillus cells have been engineered to produce calcium carbonate, a compound commonly found in limestone and is used to increase bonding efficiency in concrete. To create calcium carbonate, the bacteria must be fed a calcium source. Jonkers and Schlangen added calcium lactate (a component of milk) to the cement to power the bacteria. In the lab, they have shown that this living concrete can heal cracks up to 0.5 mm wide. Now they are testing the healing powers of bio-concrete in more representative outdoor environments.
This bio-concrete offers a sustainable and cost-savings alternative for construction projects and creates an interesting juxtaposition of the natural and human-made worlds.