Researches at the Delft Institute of Technology have created a way to use naturally occurring bacteria to in effect heal micro-fissures in concrete. Using alkaline resistant spores that can remain dormant for years in the harsh conditions found in concrete, researchers incorporated water soluble capsules containing calcium lactate and spores that only activate when moisture intrudes into the concrete. Once active, the bacteria consume the lactate as "food" and the calcium released binds with carbonates to create limestone which seals the fissure.
Here is a summary of the process with pictures from CNN. http://www.cnn.com/2015/05/14/tech/bioconcrete-delft-jonkers/