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Self-healing living concrete hits the streets for testing

Years of research into a type of concrete that can fills its own cracks may be coming to fruition as the material's creators prepare for real-world testing. If demonstrated successfully, the living-organism-assisted "bioconcrete" could transform how our cities are built.

The Delft University of Technology's Centre for Materials has been working on self-healing materials in various forms since at least 2005, which is when this type of self-healing concrete was first proposed. The need for it is not necessarily pressing (concrete is already a versatile and reliable building material), but the improvement could reduce maintenance costs enormously, among other benefits.

The material works by incorporating a type of bacteria called Bacillus pasteruii into its structure. These tiny organisms produce calcite, a hard and stable mineral, and enough calcite will fill in the tiny cracks that would otherwise admit water, threatening the integrity of the concrete or its metal reinforcement.

It's not as simple as dumping a bucket of bacteria into the mixer, though. The creatures need food to live, which as you can imagine is scarce inside a hardened block of concrete. So the problem researchers have faced is producing microscopic capsules of food (calcium lactate, a component of milk) that are durable enough to survive the mixing process but at the same time accessible to a hungry bacterium.

An early visualization of how the healing process might progressDelft University of Technology

They have a way to do it, but Dr. Henk Jonkers, who leads the project, tells BBC News that it's extremely expensive. Nevertheless, it must be done in order for them to start their real-world testing:

We have to produce the self-healing agent in huge quantities and we are starting to do outdoor tests, looking at different constructions, different types of concrete to see if this concept really works in practice.

After all, not all concrete is simply laid down as sidewalk. There are different mixture types, coatings, paints, weather stresses, and other factors that may prove incompatible with (or lethal to) the bacteria. And the sooner they start, the better; the concrete will have to be closely monitored for two full years in order to be sure no unpleasant side effects appear in the medium and long term.

If successful, the bacterial concrete could begin to be sold shortly afterward. It would be significantly more expensive than normal concrete, of course, but the price of the concrete itself is only a small part of the cost of laying down a street or raising a wall. And if the cracks in that street or wall fix themselves instead of needing constant maintenance, this living material could more than pay for itself over the life of the structure.

Devin Coldewey is a contributing writer for NBC News Digital. His personal website is