A study on the mechanical and durability properties of bacterial culture with Ground Granulated Blast Furnace Slag (GGBS) as partial replacement for cement

In concrete structures, the formation of cracks leads to reduction in the strength of the structures. Bioconcrete is an environmentally friendly material used for healing of cracks. In this study, the indigenous bacteria Bacillus cereus KOV15 obtained from the soil is used in bioconcrete with Ground Granulated Blast Furnace Slag (GGBS) as partial replacement for cement. Five different mixes of concrete such as conventional concrete and various mixes of concrete with bacterial broth culture (30% GGBS + 5% bacterial broth culture), (30% GGBS +10% bacterial broth culture), (40% GGBS + 5% bacterial broth culture) and (40% GGBS + 10% bacterial broth culture) were used to find the mechanical and durability properties and to study the microstructure of
bioconcrete. The maximum percentage increase in the cube compressive strength, the split tensile strength and the flexural strength of bioconcrete was 26.79%, 11.69% and 21.3% respectively for concrete with 30% cement replaced with GGBS and 10% bacterial broth culture in comparison
with the control concrete at the 28th day. The XRD, SEM and EDX analyses were performed to identify the calcium carbonate formation in bioconcrete. The SEM images of the bioconcrete with GGBS as replacement for cement have better hydrated form and have lesser pores than the conventional concrete. The EDX results exhibited a significant increase in the amount of calcium in the bioconcretewith 30% GGBS and 10% bacterial broth culture by 103.82% than that of the
conventional concrete.The permeability of chloride ion was very low (903.2 Coulombs) in concrete with 10% bacterial broth culture and 30% GGBS as partial replacement for cement. The water absorption was maximum (3.03%) in the conventional concrete specimens when compared to other bioconcrete specimens with bacterial broth culture and GGBS as partial replacement for cement. Bioconcrete showed very low permeability and higher acid resistance than the conventional concrete. The Load deflection studies exhibited higher ultimate load and ductility factor for bioconcrete and the failure pattern of bioconcrete indicated lesser number of cracks, minimum crack width and no shear failure pattern. The indigenous Bacillicus Cereus KOV15 strains can be used for the synthesis of green construction materials like calcite-based biocement.