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Performance characteristics of bacterial concrete - a smart biomaterial

Ramakrishnan, V.

Biomineralization is a process by which living organisms produce inorganic solids. Living organisms including bacteria form bones and teeth to natural pearls and shells. Bacteria are found everywhere in the universe and when they are present in concrete they form a biomaterial, a self-repairing material that can remediate the cracks and fissures in concrete. This paper presents the results of a novel technique in remediating cracks and fissures in concrete by utilizing microbiologically induced calcite (CaCO3). Bacillus Pasteruii, a common soil bacterium was used to induce calcite precipitation. This technique is highly desirable because the mineral precipitation induced as a result of microbial activities, is pollution free and natural. The effectiveness of this technique was evaluated by comparing the compressive strength and stiffness of cracked specimens remediated with bacteria and those of the control specimens (without bacteria). Experimental investigation was also conducted to determine the strength regaining capacity (modulus of rupture) of cracked beams remediated with different concentrations of bacteria. This paper also presents the results of a durability study on cement mortar beams treated with bacteria, exposed to alkaline, sulfate and freeze-thaw environments. Different concentrations of bacteria were used for the investigation. It was found that the use of bacteria improved the stiffness, compressive strength, modulus of rupture and durability of concrete. SEM (scanning electron microscope) was used to document the role of microbiologically induced mineral precipitation in improving the strength and durability aspects of concrete. EDX spectrometer analysis of the precipitated crystals indicated abundance of calcium and the precipitation was confirmed to be calcite.