‘Living concrete’ that can heal its own cracks

bioconcrete

Concrete remains the world’s most popular building material and is a material relied on since Roman times, 2,000 years ago. Concrete is also a material modern society is constantly trying to recreate to be more durable.

Regardless of how carefully concrete is mixed or reinforced, cracks are inevitable.

“The problem with cracks in concrete is leakage,” explains professor Henk Jonkers, of Delft University of Technology, in the Netherlands.

“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 re-bars — if they corrode, the structure collapses.”

So Jonkers came up with a new way to give concrete a longer more stable life.

“We have invented bioconcrete. That’s concrete that heals itself using bacteria,” he says.

Bioconcrete is mixed the same way as normal concrete except it has one additional ingredient. That would be the “healing ingredient”. Everything remains intact and together during the mixing process. The bacteria becomes alive and active only when the concrete cracks and water enters.

Jonkers, a microbiologist, began working on his bioconcrete project in 2006. He was asked by a  concrete technologist if it would be possible to use bacterial to create a type of self-healing concrete.

“You need bacteria that can survive the harsh environment of concrete,” says Jonkers. “It’s a rock-like, stone-like material, very dry.”

Since concrete is an extremely alkaline material and the “healing” bacteria must lie dormant and wait years before becoming activated by water, the mix needed to be precise.

For the “healing” portion of his mixture, Jonkers chose bacillus bacterial because they thrive in alkaline conditions and then 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.

To create the ideal living situation, Jonkers needed to introduce a food source, and after numerous trial and errors, he chose calcium lactate. He found that placing the bacteria and calcium lactate into capsules made from biodegradable plastic created an ideal way to add the capsules to the wet concrete mix.

Jonkers explains that when cracks begin to form, water eventually enters and opens the capsules. The bacterium then germinates, multiplies and feeds on the calcium lactate. In doing this, they combine the calcium with carbonate ions to form calcite or limestone, which closes up the cracks.

“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.”