Crack repair in concrete using biodeposition

The ability of certain bacteria to promote the precipitation of calcium carbonate, has been used advantageously for consolidation of concrete and Stone or for the desnification of sandy soils. Previous research has illustrated a reduction of the capillary permeable porosity and an increased resistance to damage processes such as chloride ingress and carbonation by this biodesposition procedure. In order to explore the crack healing potential of a biodesposition treatment, standardised cracks of 0.3 mm were produced in concrete specimens by introducing thin copper plates in fresh concrete and removing them after 1 day, or by performing splitting tests on concrete cores wrapped in fibre reinforced polymer sheets. The use of pure bacteria cultures as in the previously developed biodesposition procedure, did not result in sufficient calcium carbonate precipitation to completely bridge the cracks. Therefore, the bacteria were protected in a silica sol, resulting in the formation of a bioceramic material (sol-gel or biocer) which was able to bridge the cracks completely. The crack healing potential was illustrated by microscopic evaluation, ultrasound transmission measurements and low pressure water permeability tests. The treatment of cracks with the bacteria incorporated in the sol-gel resulted in a large reduction of the water permeability