Biocementation Influence on Flexural Strength and Chloride Ingress by Lysinibacillus Sphaericus and Bacillus Megaterium in Mortar Structures
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Date
2020
Authors
Mutitu, Daniel Karanja
Wachira, Jackson Muthengia
Mwirichia, Romano
Thiong’o, Joseph Karanja
Munyao, Onesmus Mulwa
Muriithi, Genson
Journal Title
Journal ISSN
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Publisher
Hindawi
Abstract
*e concrete/mortar durability performance depends mainly on the environmental conditions, the microstructures, and its
chemistry. Cement structures are subject to deterioration by the ingress of aggressive media. *is study focused on the effects of
Bacillus megaterium and Lysinibacillus sphaericus on flexural strength and chloride ingress in mortar prisms. Microbial
solutions with a concentration of 1.0 ×107 cells/ml were mixed with ordinary Portland cement (OPC 42.5 N) to make mortar
prisms at a water/cement ratio of 0.5. Four mortar categories were obtained from each bacterium based on mix and curing
solution. Mortar prisms of 160mm× 40mm× 40mmwere used in this study. Flexural strength across all mortar categories was
determined at the 14th, 28th, and 56th day of curing. Mortars prepared and cured using bacterial solution across all curing ages
exhibited the highest flexural strength as well as the highest percent flexural strength gain. Lysinibacillus sphaericus mortars
across all mortar categories showed higher flexural strength and percent flexural strength gain than Bacillus megaterium
mortars. *e highest percent flexural strength gain of 33.3% and 37.0% was exhibited by the 28th and 56th day of curing,
respectively. *e mortars were subjected to laboratory prepared 3.5% by mass of sodium chloride solution under the
accelerated ion migration test method for thirty-six hours using a 12V Direct Current power source after their 28th day of
curing. After subjecting the mortar cubes to Cl media, their core powder was analyzed for Cl content. From these results, the
apparent diffusion coefficient, Dapp, was approximated from solutions to Fick’s 2nd Law using the error function. Bacillus
megaterium mortars across all mortar categories showed lower apparent diffusion coefficient values with the lowest being
2.6456 ×10–10 while the highest value for Lysinibacillus sphaericus mortars was 2.8005 ×10–10. Both of the test bacteria lowered
the ordinary Portland cement Cl-ingress but Bacillus megaterium was significantly more effective than Lysinibacillus sphaericus
in inhibition.
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Citation
Mutitu, D. K., Wachira, J. M., Mwirichia, R., Thiong’o, J. K., Munyao, O. M., & Genson, M. (2020). Biocementation Influence on Flexural Strength and Chloride Ingress by Lysinibacillus sphaericus and Bacillus megaterium in Mortar Structures. Journal of Chemistry, 2020.