Emily Matchar at Smithsonian.com has an article on the state of the art of self-healing concrete. The concept:
Inspired by the human body, Jonkers [the inventor], who works at the Delft University of Technology in the Netherlands, created self-healing concrete. He embeds the concrete with capsules of limestone-producing bacteria, either Bacillus pseudofirmus or Sporosarcina pasteurii, along with calcium lactate. When the concrete cracks, air and moisture trigger the bacteria to begin munching on the calcium lactate. They convert the calcium lactate to calcite, an ingredient in limestone, thus sealing off the cracks.
The article notes that the embedded bacteria can remain dormant in the material for more than 200 years. The current high price — about $40 per square meter — means that the material will likely be reserved for use in special situations, for the time being, such as underground and underwater structures. Meanwhile, Nwakibe Kanu at HAKSblog provides a somewhat broader survey of self-healing materials. He writes:
Other self-healing materials have built-in microcapsules filled with a glue-like chemical that can repair damage. If the material cracks, the capsules break, exposing the healing agent and sealing the crack. It is possible that such a mix will be viable on a large scale within the next five years.
This is all pretty awesome.