Bio-deposition of a calcite layer on cement-based materials by brushing with agar-immobilised bacteria

Surface treatments play an important role in limiting the infiltration of water and consequently of detrimental components into concrete. Bacteria-induced carbonate mineralisation, which is a novel and environmentally friendly method for the protection of stone and cement-based materials has been proposed, to counteract the negative effects of some conventional techniques. In the present study agar was used to immobilise ureolytic bacteria by brushing the agar onto the surface of the cement paste, providing a local micro-environment. Bacterial deposition of a layer of calcite on the surface of the specimens resulted in a decrease of capillary water uptake and thus prevented the penetration of water and hazardous substances. This method of brushing semi-solid mixtures onto the surface of the cement paste specimens showed remarkable effects. It is not only more environmentally friendly and stable than the conventional surface treatment, but also easier in practice than the former bio-deposition of dipping cubes in liquid culture.