Improvements in mechanical and durability parameters of bio-engineered concrete with metakaolin as a partial substitute for cement

Abstract

One of the most important material used in the construction industry is concrete. Adaptability with steel also provides the necessary tensile strength for constructing towering structures. However, concrete is susceptible to shrinkage during the curing process which produces micro cracks. These tiny fissures provide gateways to fluids for entering into concrete. The fluids undergo various reactions under favorable conditions inside concrete reducing the pH of concrete core, making the reinforcing bars vulnerable to corrosion. This presents serious durability issues for the whole structure and bio-concrete is a solution for the same. Various studies have dealt with usages of bacillus bacteria and metakaolin to improve some parameters in concrete. Bacteria produces calcium carbonate (calcite) by urea–calcium chloride reactions inside concrete thereby reducing the threat of fluid penetration. Previous works that metakaolin reacts with calcium hydroxide (responsible for durability issues) produces secondary cementitious products, increasing the density of concrete. This study examines the usage of Bacillus megaterium MTCC 3353 in concrete with metakaolin as partial substitution for cement. It was found that the strength and durability properties exhibited by bio-concrete were overall satisfactory compared to ordinary concrete. The calcite precipitation due to the bacterial action was studied through microstructure analysis by SEM and XRD.