The aim of this research project is the development of a new type of concrete in which integrated bacteria promote self-healing of cracks. Traditional concrete does usually show some self-healing capacity what is due to excess non-hydrated cement particles present in the material matrix. These particles can undergo secondary hydration by crack ingress water resulting in formation of fresh hydration products which can seal or heal smaller cracks. However, the integration of excess cement in concrete is unwanted from both an economical and environmental viewpoint. Cement is expensive and, moreover, its production contributes significantly to global atmospheric CO2 emissions. In this study we developed a two-component self-healing system which is composed of bacteria which catalyze the metabolic conversion of organic compounds to calcite. Both components are mixed with the fresh cement paste, thus becoming an integral part of the concrete. Experimental results show that ingress water channeled through freshly formed cracks activates present bacteria which through metabolic conversion of organic mineral-precursor compounds produce copious amounts of calcite. This new bio-based two-component system may represent a new class of self-healing mechanisms which can be applied to cement- based systems. The self-healing capacity of this system is currently being quantified what should result in an estimate of the materials durability increase. A self-healing concrete may be beneficial for both economic and environmental reasons. The bacteria based concrete proposed here could substantially reduce maintenance, repair and premature structure degradation what not only saves money but also reduces atmospheric CO2 emissions considerably as less cement is needed for this type of self-healing concrete. The recent research shows that specific species of bacteria can actually be useful as a tool to repair cracks in early stage of already existing concrete structures. A highly impermeable calcite layer formed over the surface of an already existing concrete layer, due to microbial activities of the bacteria (Bacillus subtilus) seals the cracks in the concrete structure and also has excellent resistance to corrosion.
