Please use this identifier to cite or link to this item: http://hdl.handle.net/10266/6085
Title: Durability enhancement and prevention of damage in reinforced concrete structures using bacteria
Authors: Joshi, Sumit
Supervisor: Reddy, M Sudhakara
Goyal, Shweta
Keywords: Biomineralization;Ureolytic bacteria;Organic admixture;Corn steep liquor;Sulfate salt attack;Self-healing;Biogrouting;crack healing
Issue Date: 18-Feb-2021
Abstract: Microbial induced calcium carbonate precipitation (MICP) has a potential to improve the durability properties and remediation of cracks in concrete. In this study, bacterial admixed treatment and bacterial spray treatment of concrete structures with ureolytic bacteria was carried out using different media components (especially nutrient media, urea and calcium source). In the first stage of investigation, influence on the addition of bacterial culture and organic components (carbon and nitrogen content) of bacterial growth media on the setting characteristics of cement, chemical and structural properties of microbial concrete was studied. In this study, main emphasis was placed upon replacing the commercially available laboratory grade nutrient broth (NB) with corn steep liquor (CSL), which is an industrial by-product. Addition of plain NB media without bacteria severely retarded the setting of cement paste as well as significant reduction in the compressive strength was observed in concrete specimens. In fact, the addition of plain CSL media without bacteria had no adverse effect on the setting characteristics of cement paste and strength properties of concrete. While, setting characteristics of cement paste remain unaffected on the addition of bacterial culture grown in NB/CSL media. In bacterial treated concrete, MICP as a result on the addition of bacterial culture grown in NB/CSL media significantly improved the compressive strength and permeation properties. Bacterial admixed treatment (that can be used for new structures) and bacterial spray treatment (that can be used as a repair procedure) were found to be effective in MICP treatment of concrete. In the comparative analysis of CSL and NB as a nutrient media, CSL would serve as a potential alternative nutrient source for bacterial cells in microbial treatment of concrete. Further, durability of microbial treated concrete under aggressive environments was explored. This study aimed to assess the efficacy of bio-deposition as a barrier in microbial treated concrete against sulfate and chloride attack. Under sulfate exposure, bacterial admixed and bacterial spray treated mortar and concrete specimens performed well and no sign of surface scaling, strength loss and salt efflorescence was observed. During chloride exposure, microbial treatment in reinforced concrete structures significantly reduced the ingress of chloride ions in the concrete matrix and inhibition of rebar corrosion was observed. In both, bacterial admixed and bacterial spray treated reinforced concrete specimens, corrosion potential (Ecorr) and corrosion current (Icorr) values were much below the range as compared to control and depicts that corrosion is negligible. Overall, the application of MICP treatment improved the lifecycle performance of concrete under harsh sulfate environments as well as prevention of rebar from chloride induced corrosion. In present study, a suitable fly ash amended bacterial grout with optimum flowability properties was developed for the remediation of cracks in concrete. Crack treatment in horizontal orientation with injectable bacterial grout shows maximum mechanical strength recovery and significant reduction in permeation as compared to untreated concrete specimen. In case of crack treatment in vertical orientation, strength gain was minimal however permeation was improved as compared to untreated concrete specimen. The developed 40% FA amended bacterial grout with optimum rheological properties will help as an economical and environment friendly MICP technology in injection based applications for the remediation of existing cracks in concrete structures which are in service. The current work has conclusively established that MICP technique with bacterial admixed treatment and bacterial spray treatment would be effective in direct application on concrete structures. Direct incorporation of calcifying bacteria as an admixture can be used for new structures as well as bacterial spray treatment can be used as a repair procedure in concrete, respectively. From the results, it was concluded that CSL as growth media had not shown any modifications in the concrete chemical properties. On comparison with NB media, CSL may serve as a carbon and nitrogen supplement and replace yeast extract nutrient media. Utilization of biomineralization activity of calcifying bacteria in microbial treated concrete provides an innovative approach in achieving significant reduction of sulfate ingress under harsh sulfate environments and prevention of rebar from chloride induced corrosion under high chloride conditions, respectively. The developed fly ash amended biogrout will help as an economical and environment friendly MICP technology in injection based applications for the crack healing in concrete structures which are in service. The encouraging results in the current study will facilitate in upscaling this microbial based approach from lab scale to commercial scale.
Description: Ph.D. thesis
URI: http://hdl.handle.net/10266/6085
Appears in Collections:Doctoral Theses@DBT

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