Insight into the microstructural properties of bio-engineered concrete matrices and analysis by scanning electron microscopy

Cracks under loading and high permeability in marine conditions are the most common weakness in concrete. Several research have been carried out to make durable concrete structures having self-healing ability and less permeability but very few have considered the eco-friendly approach simultaneously. This work involves an attempt to improve the microstructural properties of concrete by injecting Bacillus cereus , a gram-positive calcite precipitating bacteria directly into the concrete mix as microbial culture. 100 mm cubical concrete specimens of two different strength criteria (25 MPa, 35 MPa), with and without microbial culture, were prepared and cured for various curing ages to test and analyze the effect of bacterial culture on concrete properties. An optimum optical culture density of 0.5 ± 0.1 was chosen in this form of study as it yielded maximum output in terms of calcite precipitation. 0:25 and 0:50 were the ratios of plain water to microbial culture for the preparation of bacterial concrete. Ultrasonic pulse velocity (UPV) measurement and water absorption capacity (WAC) tests were carried out on the specimens for eight different curing ages. UPV analysis showed that concrete specimens containing higher percentages of microbial culture possess higher pulse velocity than conventional concrete which is the effect of microstructural densification. 40% less permeable concrete genera were found by water absorption capacity test. Scanning electron microscopy (SEM) analysis showed the presence of higher mineral calcite precipitation in the microbial concrete microstructure than the conventional concrete. SEM also showed that with the increment of curing periods the CSH gel became well dispersed in the concrete matrix containing microbial culture. Considering all the test results, it can be concluded that the use of Bacillus cereus microbial culture in concrete mix develops better concrete genera than the conventional one. So, this technique refers to be an eco-friendly approach for developing a durable new-generation concrete in the near future.