Biocementation using Lysinibacillus sphaericus to improve building material physical-mechanical properties.

M J MARZARI, DG GONZÁLEZ, M MALDONADO TORALES, IVÁN MANRRIQUE HUGHES, KA CRESPO, PL PÁEZ, MG PARAJE, AG GUILARDUCCI.

Córdoba

Congreso; XVII Congreso Argentino de Microbiología General.; 2022

Cement is one of the most used construction materials due to its inherent benefits of durability, strength, safety, and affordability to create flexible construction materials. However, one of the inevitable consequences of long-term usage of cement-based materials is the formation of microcracks within the infrastructure. Traditional approaches which have been used to repair cracked materials are, for example, the use of epoxy resin or polyurethane to seal the cracks. Over recent years, an alternative to repair technology to address many environmental and engineering issues was an application of biological substances to enhance the mechanical properties of cement, namely biologically controlled mineralization (BCM) and biologically induced mineralization (BIM). The specifically strength improvement via bacterial mineralization is called microbial-induced calcium carbonate precipitation (MICP) and is based on the introduction of calcite-forming bacteria to increase the self-healing ability and strength of construction materials.The activity of microbial cementation on granular behavior is dependent on the ability of microbes to freely move either by injection throughout the pore space or by sufficient particle-particle contacts so that the cementation will be produced. These conditions require a balanced relationship between the microbe size and the pore between the sand particles. The scope of this work was to investigate the ability of Lysinibacillus sp. to precipitate CaCO3 using different cement mortar mixed.In this study, the feasibility of introducing calcite-forming Lysinibacillus sphaericus, into concrete pavements to improve their mechanical performance was investigated. Biocement was produced by microbial-induced calcite precipitation in the extent between the particles of granular material by draining a liquid solution containing bacteria and urea as the substrate. The biocement mortar mixed was subjected to compressive strength tests to confirm the influence of calcite precipitation on cement mortar strength. The biomortar samples were cured in an environmental chamber (23 ± 2°C - HR%≥ 95% ± 5%) and the compressive strengths were measured. L. sphaericus was grown and was mixed with water at sand: cement ratio of 1:3:0,5. Cement paste was cast into a 1x1x16 cm mold and then was left to harden at room temperature for 24 h. Cement cubes without bacterial inoculation were set up as a control. Each set of cement cubes was carried out in duplicate. We analyzed the recovery of this bacterium after these different conditions.The benefits of using MICP are that can heal the cracks from the inside, resulting in the homogeneity of the repaired materials, and is often more environmentally friendly since no toxic chemicals or high consumption of energy.