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|Microbial Remediation of Defects in Building Materials and Structures
|Reddy, M. S.
Basu, P. C.
|Bacteria, Calcite, Microbial concrete, Corrosion, Remediation of cracks
|A large number of human activities as well as natural processes, such as weathering, faults, land subsidence, earthquakes, create fractures and fissures in concrete structures that ultimately reduce the service life of the structures. “Microbial Concrete” a novel metabolic byproduct of microbially induced calcite precipitation by way of urease (urea hydrolyzing enzyme) presents a promising novel biotechnology for the enhancement of durability of building materials and structures. The objective of the present research work was to develop an effective, economic and eco-friendly microbial process, based on microbially induced calcite precipitation, to remediate the building materials and structures with self-healing ability and also to enhance their durability. The investigation was carried out on different building materials such as cement mortar, concrete and bricks. The targets were to enhance the compressive strength, reduce the permeability and corrosion protection in case of reinforced concrete. The ubiquity and importance of microbes in inducing calcite precipitation make “microbial concrete” a most important metabolic product of biomineralization that can remediate and restore such structures. Bacteria were isolated from extreme alkaline environments such as calcareous sludge, cement, alkaline soil and limestone area, so that they can sustain in the alkaline environment of cement. In the present study, a bacterium Sporosarcina pasteurii and another bacterial isolated from cement, Bacillus sp. CT-5, have been successfully employed to improve the compressive strength of building materials significantly. Microbial process increased the compressive strength by 40%. Further the efficacy of the proposed method in reducing water and chloride ion permeability is established. Initial demonstration of the corrosion protection offered by the microbial concrete is presented. Corrosion rate measurement showed that microbial process lead to around four-fold reduction in the corrosion rate of reinforced concrete specimens. The current work demonstrates that production of “microbial concrete” by urease producing bacteria on constructed facilities could enhance the durability of building materials and at least partially replace the industrial binders and provide a more sustainable alternative.
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