Concrete and bacteria are not often seen as sharing the same construction armchair, that is, unless you happen to be discussing concrete that heals itself.
Henk Jonkers from Netherlands-based Delft University of Technology has created bioconcrete, a product that can heal its own cracks and faults. Jonkers says he originally began work on the bioconcrete when he was approached by a concrete technologist who wondered whether the safety of concrete could be improved using a biological solution. This manufacturing query turned out to be the right question asked at the right time. Concrete hardens as it ages but it can also develops cracks.
According to Jonkers, a microbiologist, the cracks that form in concrete are not just unpleasant to look at, they can eventually lead to structural failures.
“The problem with cracks in concrete is leakage,” said Jonkers. “If you have cracks, water comes through—in your basements, in a parking garage. Secondly, if this water gets to the steel reinforcements—in concrete we have all these steel rebars—if they corrode, the structure collapses.”
It has taken Jonkers and his team three years to produce this self-healing prototype, needing to overcome the most obvious obstacle: finding bacteria that can survive the harsh environment of concrete.
“It’s a rock-like, stone-like material, very dry,” said Jonkers. To address this dry hardship, the team picked bacillus bacteria for its hardiness and longevity. The bacteria and its food source, calcium lactate, are packed into tiny capsules that dissolve when water enters the concrete cracks. Once released, the bacteria consume the calcium lactate, causing a chemical reaction that creates limestone, which then fills in the gaps.
A lakeside lifeguard station in the Netherlands was used as the site for the first application of bioconcrete. The test for the prototype turned out to be positive.
“It is combining nature with construction materials,” said Jonkers. “Nature is supplying us a lot of functionality for free—in this case, limestone-producing bacteria. If we can implement it in materials, we can really benefit from it, so I think it’s a really nice example of tying nature and the built environments together in one new concept.”
For over 2,000 years, concrete has been used as a popular building material, dating back to when the Romans built the Pantheon. It is now a standard material for everything from road surfaces to roadway infrastructure items, such as sidewalks, curbs, and gutters.
The bioconcrete is mixed just like regular concrete, but with an extra ingredient — the “healing agent.” It remains intact during mixing, only dissolving and becoming active if the concrete cracks and water gets in.
Concrete is extremely alkaline and the “healing” bacteria must wait dormant for years before being activated by water. Jonkers chose bacillus bacteria for the job, because they thrive in alkaline conditions and produce spores that can survive for decades without food or oxygen. “The next challenge was not only to have the bacteria active in concrete, but also to make them produce repair material for the concrete — and that is limestone,” Jonkers explains.
In order to produce limestone the bacilli need a food source. Sugar was one option, but adding sugar to the mix would create soft, weak, concrete. In the end, Jonkers chose calcium lactate, setting the bacteria and calcium lactate into capsules made from biodegradable plastic and adding the capsules to the wet concrete mix.
When cracks eventually begin to form in the concrete, water enters and open the capsules. The bacteria then germinate, multiply and feed on the lactate, and in doing so they combine the calcium with carbonate ions to form calcite, or limestone, which closes up the cracks.
Jonkers said he hopes his concrete could be the start of a new age of biological buildings. If so, the impact on architectural and engineering methodologies might be profound.
“It is combining nature with construction materials,” he says. “Nature is supplying us a lot of functionality for free — in this case, limestone-producing bacteria.
If we can implement it in materials, we can really benefit from it, so I think it’s a really nice example of tying nature and the built environments together in one new concept.”
Sources: CNN, Inhabitat