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Self-Healing Concrete Uses Bacteria For Healing
Self-healing concrete that is able to heal its own hairline fractures is under development at Delft University of Technology in Delft, the Netherlands. Bacteria placed in concrete buildings could use calcium lactate to make calcite, a natural form of cement, when activated by water.
Moreover, the bacteria can take on a dormant spore state for long periods up to 50 years, according to Jonkers without food or water. He compares them to seeds waiting for water to germinate.
To keep the spores from activating in the wet concrete mix, and to keep them and their calcium lactate food from affecting the quality of the concrete, Jonkers and his colleagues first set both into ceramic pellets 2 to 4 millimetres wide and then added them to the concrete.
Only when tiny cracks form in the concrete opening up the pellets and water seeps inside will the bacteria activate and begin to consume the food that has also been freed. As they feed, they combine the calcium with oxygen and carbon dioxide to form calcite essentially pure limestone.
Fans of sf writer J.G. Ballard will recall the self-healing buildings in his 1962 short story The Thousand Dreams of Stellavista:
Building, heal thyself - with these links:
Read more at New Scientist.
Unfortunately, most organisms keel over in a pH above 10, which is typical of concrete. To find bacteria that are happy in such an alkaline environment, Jonkers and his colleagues looked to soda lakes in Russia and Egypt where the pH of the water is naturally high and found that some strains of Bacillus thrived there.
It was a beautiful room all right, with opaque plastex walls and white fluo-glass ceiling, but something terrible had happened there. As it responded to me, the ceiling lifting slightly and the walls growing less opaque, reflecting my perspective-seeking eye, I noticed that curious mottled knots were forming, indicating where the room had been strained and healed faultily.
Engineers at Bristol University, with funding from the Engineering and Physical Sciences Research Council (EPSRC) developed the technique. Here's how it works.
The intent is that when squeezed under pressure (during a quake), the nano polymer particles will flow into cracks and harden to form a solid material.
The idea of a "self-healing" surface is part of a larger set of ideas called "autonomous materials systems."
If the coating is scratched, polymer capsules just a few hundred nanometers thick rupture and release their healing contents.
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