Browsing by Author "Mutitu, Daniel Karanja"

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    Biocementation Influence on Flexural Strength and Chloride Ingress by Lysinibacillus sphaericus and Bacillus megaterium in Mortar Structures
    (Hindawi, 2020-05) Mutitu, Daniel Karanja; Wachira, Jackson M.; Mwirichia, Romano K.; Thiong’o, Joseph Karanja; Munyao, Onesmus Mulwa; Genson, Muriithi
    The 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. This 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 160 mm × 40 mm × 40 mm were 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. The highest percent flexural strength gain of 33.3% and 37.0% was exhibited by the 28th and 56th day of curing, respectively. The 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 12 V 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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    Effect of microbial biocementation on physicochemical And mechanical properties of mortar Made from portland cements
    (Daniel Karanja Mutitu, 2020-11) Mutitu, Daniel Karanja
    Microorganisms in soil and water play a significant role in physico-chemical and mechanical properties as well as the durability of building materials. The microorganisms can either contribute to the improvement or deterioration of the materials. Beneficial microorganisms may deposit calcium carbonate in cement mortar or concrete through a process called microbial biocementation. These deposits exhibit binding properties for protecting and consolidating various building materials. Whereas the effect of Bacillus bacteria on fully hardened/cured mortar/concrete is well documented, the effect of such microorganisms on fresh mortar and concrete paste has not been fully investigated. Further, this study examined the microorganisms' biominerals, their chemical composition, and their role in the enhancement of nucleation on cement hydration. The Bacillus species under this study are commonly found in soil/water, are non-pathogenic and are urease active. Bacterial species, Lysinibacillus sphaericus, Sporosarcina pasteurii, and Bacillus megaterium were incorporated separately into the mortar-making mixing water at a concentration of 1.0 × 107 cells/mL. Mortar prisms with 0.5 watercement (w/c) ratio were cast using selected commercial Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC). Some prisms were then cured at room temperature in a microbial solution composed of bacteria, urea, and calcium acetate/calcium chloride, while others were cured in tap water. Lower normal consistency results from microbial mortar pastes than non-microbial pastes in both OPC and PPC were observed. This implied reduced water demand and improved workability. Initial and final setting time were generally lowered, with the OPC paste with Lysinibacillus sphaericus showing the highest reduction. The resultant chemical compounds formed in the mortar were analyzed using Scanning Electron Microscopy (SEM), powder X-ray Diffraction (XRD), and Fourier Transform Infrared (FTIR). Bavenite, Al2Be2Ca4H2O28Si9, and calcite, CaCO3, were found to be the resultant microbial cement hydration products. Compressive and flexural strength gain was observed after the 14th day of curing with the highest compressive and flexural strength gain observed at the 56th day of curing at 19.8 % and 37.0 % respectively for OPC mortars that had Lysinibacillus sphaericus. Rapid accelerated chloride and sulphate penetration tests were performed on the mortar prisms by exposing them to a media of 3.5 % by mass of sodium chloride and sodium sulphate separately for thirty-six hours using a 12V DC power source. The migration diffusion coefficient, Dmig, and apparent diffusivity coefficient, Dapp, for both the Cl1- and SO4 2- for mortar prisms were determined. Dapp was lowered from 3.5340 × 10-10 m2/s to 2.5449 × 10-10 m2/s and from 6.4810 × 10-10 m2/s to 4.5179 × 10-10 m2/s for Cl1- and SO4 2- respectively in PPC mortars that had Bacillus megaterium. After the 28th day of curing, water sorption change was determined across the mortar categories. Water sorption was lowered in the range of 47.8 % to 68.4 %. PPC mortars that had Bacillus megaterium exhibited a water sorptivity coefficient reduction from 0.0289 to 0.0093. The results show that the incorporation of the selected Bacillus species under this study improves the physico-chemical and mechanical properties of the test cements significantly
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    Influence of Lysinibacillus sphaericus on compressive strength and water sorptivity in microbial cement mortar
    (Elsevier, 2019-11) Mutitu, Daniel Karanja; Wachira, Jackson M.; Mwirichia, Romano K.; Thiong'o, Joseph Karanja; Munyao, Onesmus Mulwa; Muriithi, Genson
    Cement structures are subject to degradation either by aggressive media or development of micro/macro cracks which create external substance ingress pathways. Microbiocementation can be employed as a self-intelligent solution to this deterioration process. This paper presents study results on the effects of Lysinibacillus sphaericus microbiocementation on Ordinary Portland cement (OPC), normal consistency, setting time, soundness, compressive strength and water sorptivity. Microbial solutions with a concentration of 1.0 107 cells/ml were mixed with OPC to make prisms at a water/cement ratio of 0.5. Mortar prisms of 160 mm 40 mm x 40mm were used in this study. A maximum compressive strength gain of 17% and 19.8% was observed on the microbial prism at the 28th and 56th day of curing respectively. A minimum of 0.0190 and a maximum of 0.0355 water sorptivity coefficient was observed on the OPC microbial prism and OPC control prism, after 28th day of curing respectively. Scanning electron microscope images taken after the 28th day of curing showed formation of vast calcium silicate hydrates and more calcite deposits on microbial mortars. Statistical findings of this study indicate that Lysinibacillus sphaericus significantly retarded both the setting time and normal consistency, but has no influence on the mortar soundness.
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    Influence of Lysinibacillus sphaericus on compressive strength and water sorptivity in microbial cement mortar
    (Elsevier, 2019-11) Mutitu, Daniel Karanja; Wachira, Jackson M.; Mwirichia, Romano K.; Thiong'o, Joseph Karanja; Munyao, Onesmus Mulwa; Muriithi, Genson
    Cement structures are subject to degradation either by aggressive media or development of micro/macro cracks which create external substance ingress pathways. Microbiocementation can be employed as a self-intelligent solution to this deterioration process. This paper presents study results on the effects of Lysinibacillus sphaericus microbiocementation on Ordinary Portland cement (OPC), normal consistency, setting time, soundness, compressive strength and water sorptivity. Microbial solutions with a concentration of 1.0 107 cells/ml were mixed with OPC to make prisms at a water/cement ratio of 0.5. Mortar prisms of 160 mm 40 mm x 40mm were used in this study. A maximum compressive strength gain of 17% and 19.8% was observed on the microbial prism at the 28th and 56th day of curing respectively. A minimum of 0.0190 and a maximum of 0.0355 water sorptivity coefficient was observed on the OPC microbial prism and OPC control prism, after 28th day of curing respectively. Scanning electron microscope images taken after the 28th day of curing showed formation of vast calcium silicate hydrates and more calcite deposits on microbial mortars. Statistical findings of this study indicate that Lysinibacillus sphaericus significantly retarded both the setting time and normal consistency, but has no influence on the mortar soundness.
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    Influence of Starkeya novella on Mechanical and Microstructural Properties of Cement Mortars
    (Hindawi, 2020-04) Munyao, Onesmus Mulwa; Thiong’o, Joseph K.; Wachira, Jackson M.; Mutitu, Daniel Karanja; Mwirichia, Romano K.
    Cement-based materials are subject to degradation during their service life. Most of the structural failures have been associated with corrosion of the rebar due to chloride ingress, alkali aggregate reaction, and/or sulfate attack. Microbial activities, especially in waste water collection points such as sewer lines, may compromise the integrity of concrete structures. This study reports an experimental work carried out to determine the effect of Starkeya novella bacteria species on mechanical and microstructural properties of cement mortars. Mortar prisms were prepared from selected ordinary Portland cement (OPC) and Portland pozzolana cement (PPC) in Kenyan markets. Bacterial solution of 1.0 × 107 cell/mL concentration was used as either mix water, curing media, or both. Distilled water was used to prepare mortar prisms for control samples. Compressive strength was determined after the 7th, 28th, 56th, and 90th day of curing. Scanning electron microscopy (SEM) was tested on both bacterial and control mortar prisms after the 28th day of curing. Both PPC and OPC exhibited significant decrease in compressive strength for bacterial-prepared mortars as compared to controls. SEM analysis showed extreme erosion on the microstructure of the microbial mortars. This was denoted by massive formation of ettringite and gypsum which are injurious to mortar/concrete.