From the Delft University of  Technology in the Netherlands, self-repairing concrete which uses bacteria that excrete calcium, developed by faculty member Henk Jonkers:

Instead of costly humans having to maintain and repair the concrete, it would be ideal if the concrete would be able to heal itself. This is now possible with help of special bacteria. These bacteria are called extremophiles, because they love to live in extreme conditions. In dry concrete for example they will not only live, but they will actively produce copious amounts of limestone. With this calcium carbonate-based material the little construction workers can actively repair occurring cracks in a concrete structure.

This novel type of self-healing concrete will lead to enormous savings on maintenance and repair costs. Also the sustainability of concrete will increase dramatically, because of a lower demand for natural resources such as cement. This will lead to lower CO2 emissions and change our way of reasoning. Instead of building against nature, biological materials and processes will be integrated into traditional engineering materials and processes.

Via William Myers in his post Growing Respect for Dirt, on the Design Blog at the Cooper-Hewitt, the Smithsonian’s National Design Museum.