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The concept of bacteria-based self-healing concrete was developed in the Netherlands, has received considerable interest from the press and is the subject of numerous UK research programmes.
Concrete often cracks due to a variety of processes [see ´construction related cracks´] and in certain circumstances can self-heal those cracks up to a width of 0.3mm [see ´autogenous healing´].
Chemical additives (usually crystalline) can also be added to fresh concrete to improve this self-healing process.
The principle mechanism of bacterial crack healing is that the bacteria themselves act largely as a catalyst, and transform a precursor compound to a suitable filler material which effectively seals newly formed cracks. When bacteria spores are directly added to the concrete their lifetime was found to be limited. Therefore, studies are now examining the effect of bacterial spores and the required organic biomineral precursor compound immobilized in porous expanded clay particles. This has been shown to heal cracks with a width of 0.15mm.
Unfortunately incorporating the clay particles also leads to a 50% reduction in 28 day strength.
Acknowledgement: Concrete Society