Key test for re-healable concrete – “Experimental concrete that patches up cracks by itself is to undergo outdoor testing.” BBC Science post about concrete being developed at Delft Technical University that “contains limestone-producing bacteria, which are activated by corrosive rainwater working its way into the structure.”
“In the lab we have been able to show healing of cracks with a width of 0.5mm – two to three times higher than the norms state …”
From the Delft site:
Repairing cracks in concrete structures is a time consuming, costly but necessary business. TU Delft is researching how the self-healing capacity of concrete structures can be improved by using calcite-precipitating bacteria and what conditions are necessary for these bacteria to thrive.