Manual healing of cracks in concrete by the use of bacteria

As synthetic polymers, currently used for concrete repair, may be harmful to the environment, the use of a biological repair technique, that is ecologically sound, is investigated. Bacteria such as Bacillus sphaericus are able to precipitate calcium carbonate on their cell consituents and in their micro-environment by conversion of urea into ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of carbonate as calcium carbonate in a calcium rich environment. These precipitated CaCO3 crystals can be used for healing of cracks. The crack healing potential of bacteria and traditional repair techniques, such as epoxy or grout injection, are compared in this study. The crack healing efficiency was illustrated by water permeability tests, ultrasound transmission measurements and visual examination. It was shown that pure bacteria cultures were not able to bridge the cracks probably because bacterial activity was stopped due the high pH in concrete. However when bacteria were protected in silica gel and a calcium source was provided, the biological treatment was able to fill the crack completely