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Science: 

The concrete that can heal itself

This could be a thing of the past, with bioconcrete.

This could be a thing of the past, with bioconcrete.

It’s probably not that high up on your list of priorities, but concrete cracking is quite a big problem in building circles. If concrete cracks, then water gets in, which isn’t just a problem in terms of leaks but even more serious if it gets through to the steel reinforcements which can corrode and… there’s no nice way to say this: buildings can collapse.

Wouldn’t it be great if concrete could fix itself, then, giving us time to worry about things that actually matter, like internet conspiracy theories? Well, your wish is a Dutch scientist’s command, as nine years of work has resulted in bioconcrete: building material that can fix itself using bacteria. In simple terms, the water sets off a chain reaction that sees the bacteria produce limestone to plug the gaps.

That sounds simple enough, so why nine years? Well, the actual solution of using bacteria was relatively simple, and decided upon after just three. The trouble is that the extremely alkaline concrete isn’t the ideal material to sustain life. As Henk Jonkers of Delft University of Technology told CNN, “You need bacteria that can survive the harsh environment of concrete. It’s a rock-like, stone-like material, very dry.”

The solution was to use bacillus bacteria. They ‘thrive’ in alkaline conditions and make spores that can hang on for decades without food or oxygen. Handy, as Jonkers’ solution would see bacteria lying dormant, to be activated by water leaking through cracks.

Calcium lactate – the food source the bacteria need when they awaken – is mixed into the bioconcrete in biodegradable capsules. Delicious sugar was considered, but could have weakened the concrete –  so hard luck, bacteria.

When the bioconcrete cracks, the water causes the capsules to open, at which point the bacteria multiply and feed on the calcium lactate. During the act, the bacteria combine calcium with carbonate ions to form calcite – limestone to you or me. This limestone fills the cracks, and the concrete is as good as new.

“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,” Jonkers concludes.

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