Concrete is a prerequisite material for infrastructural development, which is required to be sufficiently strong and durable. It consists of fine, coarse, and aggregate particles bonded with a fluid cement that hardens over time. However, micro cracks development in concrete is a significant threat to its durability. To overcome this issue, several treatments and maintenance methods are adopted after construction, to ensure the durability of the structure. These include the use of bio-engineered concrete, which involved the biochemical reaction of non-reacted limestone and a calcium-based nutrient with the help of bacteria. These bio-cultures (bacteria) act as spores, which have the ability to survive up to 200 years, as they are also found to start the mineralization process and the filling of cracks or pores when in contact with moisture. Previous research proved that bio-engineered concrete is a self-healing technology, which developed the mechanical strength properties of the composite materials. The mechanism and healing process of the concrete is also natural and eco-friendly. Therefore, this study aims to critically analyze bio-engineered concrete and its future potentials in the Structural Engineering field, through the use of literature review. The data analysis was conducted in order to provide gradual and informative ideas on the historical background, present situation, and main mechanism process of the materials. According to the literature review, bio-engineered concrete has a promising outcome in the case of strength increment and crack healing. However, the only disadvantage was its less application in the practical fields. The results concluded that bio-engineered concrete is a new method for ensuring sustainable infrastructural development. And also, it indicated that more practical outcome-based analysis with extensive application in various aspects should be conducted, in order to assess the overall durability.
Concrete is an artificial manmade building material which is obtained by carefully permitting proportioned mixture of cement, sand, stone/brick chips and water. Appropriate adjustments of these ingredients can lead concrete with vast ranges of properties. Although concrete can tolerate compressive forces like natural stone, it is prone to cracking due to tensile forces. Thus, crack formation is a widespread phenomenon in concrete, which allows different kinds of foreign substances and water into the concrete structures and reduces the life span of the infrastructures. The possibility of cracking can increase with time due to the variation in humidity and temperature. Maintaining or repairing concrete-based structures can be very costly. Use of self-healing concrete using microbial agent is demonstrated very beneficially in the present scenario for the construction of durable structures. It is proved to be advantageous for improving the properties of concrete and also for reducing the maintenance costs. In this study 100×100×100 mm cubical concrete specimens were prepared with or without using Escherichia coli bacteria and periodically subjected to compressive and split tensile strength test. About 10% and 23% increment in compressive and split tensile strengths were respectively observed after 28 days of curing period due to addition of E. coli bacteria in concrete. Later on, UPV and SEM analysis were also performed to evaluate material properties. SEM analysis also confirmed the crystalline structures within the powdered mortar sample. Hence, the use of E. coli bacteria in concrete is arranged towards increasing sustainability and decreasing the all-out cost-of-ownership for structures.
Cracks under loading and high permeability in marine condition are the most common weakness in concrete. Several researches have been carried out to make durable concrete structure 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 test and Water Absorption Capacity (WAC) test 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.
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