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Improvement of tensile strength and durability of mortar through bio cementation

Throughout the field of construction, intrinsic brittleness of the mortar that lead to cracking, especially after plastering, has been frequently observed, which makes it a common hurdle in most of the constructed structures, due to the significant loss of water tightness and durability. Cementous structures are subject to damage continuously by harassment conditions. Therefore, special biological systems can be exploited to overcome such problems. Many bacterial species have been employed to precipitate calcium carbonate through the oxidation of organic carbon, changing the properties of the construction material. The oxidation process would fill the pores between cement matrices, which shows significant decrease in the porosity, permeability and capillary water penetration. Deposition of calcium carbonate by bacteria is a phenomenon known as microbiologically induced calcite precipitation (MICP), biomineralization, or bio cementation, which considered as natural and eco-friendly process. Such deposition is a promising practice for integrating and protecting various building materials. The strength refinement is due to growth of filler material inside the pores of the cement matrix. In addition, a modification in pores’ size, distribution, and total volume are also noted, that could enhance durability properties. Due to the relative dryness and shortage of nutrients required for bacterial growth in concrete, those common bacteria unable to thrive. Some extremophiles spore forming species are able to survive in such hostile environment and boost the durability, compressive strength, and self-healing and repairing of micro-cracks in the cement concrete. Bacillus spizizenii 6633 was added to cement mortar, and found that the tensile strength was increased up to 12.6%, and the deterioration was decreased through the reduction of the microcracks by self-healing process.