Articles: Department of Physical Sciences

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Anti-Bacterialactivities And Phytochemical Screening Of Extracts Of Different Parts Of Thalictrum Rhynchocarpum
(2013) Mayeku, Philip Wafula; Hassanali, Ahmed M.; Kiremire, Bernard T.; Odalo, Josiah O.; Hertweck, Christian
Parts of the plant Thalictrum rhyncocarpum are used in herbal medicine in Kenya to treat various infections. The aim of this study was to evaluate in-vitro anti-bacteria activities and phytochemical profiles of solvent extracts of the leaves, stem bark and root of Thalictrum rhyncocarpum against Bacillus subtilis-6633, Staphylococcus aures-SG 511, Escherichia coli SG 458, Pseudomonus aeruginosa-K799/61 and Mycobacterium vaccae-10670. Anti-bacterial activity tests were carried out using disc diffusion assay and tube dilution technique, and phytochemical screening was carried out through Thin Layer Chromatography. The crude extracts showed antibacterial effects on M. vaccae, P. aeruginosa and B. subtilis. M. vaccae was most sensitive, particularly to the methanol root extract. Phytochemical screening of the extracts suggested the presence of glycosides and alkaloids in the stem bark and root extracts, and flavonoids and triterpenes in the leaf extracts. The study showed interesting levels of activities of solvent extracts of different parts of T. rhyncocarpum against some of the bacteria tested (M. vaccae, P. aeruginosa and B. subtilis). The results provide some scientific rationale for the traditional use of the plant in Kenya to treat different microbial infections.
Beneficiation of Iron in Thermal-Reduced Ilmenite by Magnetic Separation
(2013) Kariuki, Warui S.; Wachira, Jackson M.; Mutembei, Peterson K.; Waithaka, Peter N.
ncreasing demands for Iron in countries development, and lack of conventional reducing agents has resulted into sourcing of alternative ways of beneficiating the iron ore. This paper reports on the study that was done to concentrate low grade iron ores. Raw biomass / low grade iron ore mixed in the ratio of 1:10 in a reducing environment was heated in a controlled air condition to increase the magnetic susceptibility of iron in the ore. The magnetic portion of the resulting product was separated using a horse shoe-magnet. This resulted into concentrating the ore from 45.6% - 53.1 % to 76.3%- 82.2%. This gave an ore that could be fed to a blast furnace for extraction of iron.
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.
Bioremediation of mortar made from Ordinary Portland Cement degraded by Thiobacillus thioparus using Bacillus ﬂexus
(Heliyon, 2021-06) Ngari, Reginah Wangui; Thiong'o, Joseph K.; Wachira, Jackson M.; Muriithi, Genson; Mutitu, Daniel K.
Cement is widely used as a construction material in the construction industry. However, there are challenges affecting its durability efﬁcacy. Cement mortar/concrete is subject to degradation by aggressive ions such as sulphates and chlorides. Sulphates can be introduced into the concrete or mortar by Sulphur producing bacteria of the species Thiobacilli. Microbiologically induced CaCO3 precipitation (MICP) has found its application in bioremediating cement based materials. It has been found to be environmental friendly. However, no work has been reported on bioremediation of biodegraded cement based materials. This paper presents ﬁndings of possible bioremediation of mortars after undergoing biodegradation. Bacillus ﬂexus, a beneﬁcial bacterium was used. The control mortars were prepared using Ordinary Portland Cement (OPC). The test mortars were prepared and cured in a solution of Thiobacillus thioparus, a Sulphur oxidizing bacteria, deleterious bacterium for 14, 28, 56 and 90 days. Compressive strength analysis was conducted on the 14 day of curing. Results showed that the lowest compressive strength was recorded on the 90 th th th th ,28 ,56 and 90 day as 31.02 MPa. This was a 34.17 % loss in compressive strength. Another category of mortar cured in Thiobacillus thioparus for 28 days was bioremediated for 28 days using Bacillus ﬂexus solution. Compressive strength and Scanning Electron Microscopy (SEM) analyses were then done. The results show a compressive strength of 45.83 MPa at the 56 th day. This represents a 99.91 % strength recovery from biodeterioration. The SEM analysis results revealed a denser material. This was due to massive precipitation of calcium carbonate in the mortar matrix and pores/voids for bioremediated mortars as opposed to the biodegraded mortars. The results further revealed reduced ettringite crystals on the bioremediated mortars. Bacillus ﬂexus could perhaps be used in restoring lost compressive strength as well as in sealing voids in degraded concrete in sewer lines and other cement based materials. This could improve on its efﬁcacy with minimal repair.
Carbon storage in the seagrass meadows of Gazi Bay, Kenya
(2017-05-10) Michael, Githaiga N.; Kairo, James G.; Gilpin2, Linda; Huxham, Mark
Vegetated marine habitats are globally important carbon sinks, making a significant contribution towards mitigating climate change, and they provide a wide range of other ecosystem services. However, large gaps in knowledge remain, particularly for seagrass meadows in Africa. The present study estimated biomass and sediment organic carbon (Corg) stocks of four dominant seagrass species in Gazi Bay, Kenya. It compared sediment Corg between seagrass areas in vegetated and un-vegetated ‘controls’, using the naturally patchy occurence of seagrass at this site to test the impacts of seagrass growth on sediment Corg. It also explored relationships between the sediment and above-ground Corg, as well as between the total biomass and above-ground parameters. Sediment Corg was significantly different between species, range: 160.7–233.8 Mg C ha-1 (compared to the global range of 115.3 to 829.2 Mg C ha-1). Vegetated areas in all species had significantly higher sediment Corg compared with un-vegetated controls; the presence of seagrass increased Corg by 4–6 times. Biomass carbon differed significantly between species with means ranging between 4.8–7.1 Mg C ha-1 compared to the global range of 2.5–7.3 Mg C ha-1. To our knowledge, these are among the first results on seagrass sediment Corg to be reported from African seagrass beds; and contribute towards our understanding of the role of seagrass in global carbon dynamics.
Cementing material from rice husk-broken bricks-spent bleaching earth-dried calcium carbide residue
(2012) Wachira, Jackson M.; Muthakia, Gerald K.; Thiong’o, Joseph K.
A cementious material, coded CSBR (Carbide residue Spent bleaching earth Broken bricks and Rice husks), was made from dried calcium carbide residue (DCCR) and an incinerated mix of rice husks (RH), broken bricks (BB) and spent bleaching earth (SBE). Another material, coded SBR (Spent bleaching earth Broken bricks and Rice husk ash), was made from mixing separately incinerated RH, SBE and ground BB in the same ash ratio as in CSBR. When CSBR was inter-ground with Ordinary Portland Cement (OPC), it showed a continued decrease in Ca(OH)2 in the hydrating cement as a function of curing time and replacement levels of the cement. Up to 45 % replacement of the OPC by CSBR produced a Portland pozzolana cement (PPC) material that passed the relevant Kenyan Standard. Incorporation of the CSBR in OPC reduces the resultant calcium hydroxide from hydrating Portland cement. The use of the waste materials in production of cementitious material would rid the environment of wastes and lead to production of low cost cementitious material.
Characterization of cerium doped yttrium gadolinium aluminate garnet (Y-Gd)3Al5O12:Ce3+ phosphor thin films fabricated by pulsed laser deposition
(2015) Wako, Ali Halake; Dejene, F. B.; Swart, H.C.
Thin films of cerium doped yttrium gadolinium aluminate garnet (Y-Gd)3Al5O12:Ce3+ (YGAG:Ce) were grown on Si(100) substrates by a pulsed laser deposition (PLD) technique using a 266 nm Nd:YAG pulsed laser under varying deposition conditions, namely; substrate temperature, substrate – target distance, number of laser pulses and the working atmosphere during the film deposition process. The effect of annealing temperatures on the structure and luminescence properties of the as-deposited (YGAG:Ce) thin films were analysed. Photoluminescence (PL) data were collected in air at room temperature using an F-7000 FL Spectrophotometer. A slight shift in the wavelength of the PL spectra was observed from the thin films when compared to the PL spectra of the phosphor in powder form, which is probably due to a change in the crystal field. The PL intensity of the samples increased as the annealing temperature was increased from 400 oC to around 700 oC and then decreased with continued increase in the annealing temperature.
Characterization of composite material from the copolymerized polyphenolic matrix with treated cassava peels starch
(Heliyon, 2020-07) Kariuki, Stephen W.; Wachira, Jackson M.; Kawira, Millien; Murithi, Genson L.; Marangu, Joseph M.
Conventional binders in the particleboards formulation involve use of formaldehyde resins. Epidemiologic studies show that formaldehyde is carcinogenic. Efforts to reduce formaldehyde emissions by use of scavengers has not been proven to reduce the emission. Molecular bonding of biobased adhesive molecules with lignocellulose materials provides an alternative way of producing composite material. In this study, maize stalk (MS), rice husks (RH) and sugarcane bagasse (SB) were used as sources of lignocellulose materials for particleboard formulation. SB, MS and RH were collected from their respective sites, sorted and dried. MS and RH were ground. Lignin content determination was done by drying lignocellulose material at 105 C. Lignocellulose materials were prepared by hydrolysis of dried lignocellulose material with sodium hydroxide. Oxidized starch was prepared by oxidation of cassava peel starch using alkaline hydrogen peroxide. Particleboards were formulated through starchlignocellulose polymerization at 60 C compressed with 6.5 Nmm 2 pressure. Characterization of raw materials and formulated particleboards was done using XRD for mineralogical analysis, FTIR and NMR for elucidation of functional groups transformation. The results showed that esteriﬁcation is the main process of chemical bonding in the particleboard formulation due to reaction between COOH from starch and and OH- from lignocellulose. Etheriﬁcation between hydroxyl groups from starch with hydroxyl groups from lignocellulose material. RH combined more through silication process with cassava peels starch than RH and SB showing materials containing high cellulose and hemicellulose content are more compatible. Composite materials formulated were used to produce medium density particleboards that can be used for making furniture and room partitioning.
Characterization of Local Nano-Heat Transfer Fluids for Solar Thermal Collection
(Hindawi, 2020-08) Kawira, Millien
Performance of organic oils in solar thermal collection is limited due to their low thermal conductivity when they are compared to molten salt solutions. Extraction of organic oils from plants can be locally achieved. 'e purpose of this study was to investigate the eﬀect of use of copper nanoparticles in some base local heat transfer ﬂuids (HTFs). Addition of volume fraction of 1.2% of the copper nanoparticles to oil-based heat transfer ﬂuids improved their thermal conductivity as deduced from the thermal heat they conducted from solar radiation. 'e oil-based copper nanoﬂuids were obtained by preparation of a colloidal solution of the nanoparticles. Impurities were added to increase the boiling point of the nano-heat transfer ﬂuids. Stabilizers were used to keep the particles suspended in the oil-based ﬂuids. 'e power output of the oil-based copper nano-heat transfer ﬂuids was in the range of 475.4 W to 1130 W. 'e heat capacity of the steam in the heat exchanger was 93.7% dry and had a thermal capacity of 5.71 × 10 3 to 89.1 Js kJ. 'e heat rate of ﬂow of the oil-based copper nano-heat transfer ﬂuids was an average of 72.7 Js −1 −1 ·kg −1 −1 . 'e thermal eﬃciency for the oil-based copper nano-heat transfer ﬂuids ranged from 0.85 to 0.91. 'e average solar thermal solar intensity was in the range 700 Wm ·kg . 'e heat exchanger used in this study was operating at 4.15 × 10 −2 −2 to 1180 Wm 3 kJ and a temperature of 500.0 ° C. 'e heat transfer ﬂuids entered the exchanger at an average temperature of 381 ° C and exited at 96.3 ° C. 'e average temperatures of operation ranged between 394.1 C and their heat coeﬃcient ranged between 290.1 Wm −2 ° −2 ° C and 254.1 Wm ° C and 219.7 ° C with respective temperature eﬃciencies ranging between 93.4% and 64.4%. It was established that utilization of copper nanoparticles to enhance heat transfer in oil-based local heat transfer ﬂuids can mitigate energy demand for meeting the world’s increasing energy uses, especially for areas inaccessible due to poor land terrain.
Characterization of Prototype Formulated Particleboards from Agroindustrial Lignocellulose Biomass Bonded with Chemically Modified Cassava Peel Starch
(Hindawi, 2019) Kariuki, Stephen Warui; Wachira, Jackson M.; Kawira, Millien; Murithi, Genson Leonard
Conventional methods of making particleboards utilize wood chips. +is has resulted in a decrease in the tree cover due to the increase in wood demand. +e effect has been climatic change. Wood is bound using phenol formaldehyde resin. Because of the decrease in the forest cover, alternative lignocellulose materials are required. In this study, lignocellulose materials used include sugarcane bagasse, maize stock, and rice husks. +e cassava-starch mix with borax was used as a binder in particleboard formulation. +e lignin content was determined, and its effect on properties of boards was investigated. +e resultant composite material was molded at a pressure of 6.5N/mm2 and at 30°C. +e resultant particleboards had mean densities ranging from 0.604 to 0.611 g/cm3. +e modulus of elasticity ranged from 2364.2N/mm2 to 3329.93N/mm2, modulus of rupture ranged from 13.55N/mm2 to 14.83 N/ mm2, and internal bonding ranged from 1.613N/mm2 to 2.370N/mm2. +e performance of the board was dependent on the lignocellulose material used. Fourier transform infrared spectroscopy analysis showed that main chemical bonding in the particleboard resulted from esterification of –COOHfrom lignocellulose and OH- from starch.+e particleboards formulated were found to be of low-density-fibre standard used in a similar manner to the conventional low-density particleboards
Chemical composition and mosquito repellency of essential oil of Conyza newii propagated in different geographical locations of Kenya
(John Wiley & Sons, 2014) Mayeku, Philip Wafula; Omollo, N. I.; Odalo, O. J.; Ahmed, Hassanali
Previously, essential oil of Conyza newii (Asterale: Asteracea, Oliv. & Hiern) growing in the northern part of West Pokot (35◦E, 1◦N) of Kenya was shown to be highly repellent [RD50 =8.9×10−5 mg/cm2, 95% confidence interval (CL)] to Anopheles gambiae s.s. Fumigant toxicity of the oil to the mosquito was also demonstrated. The major constituents of the oil were found to be monoterpenoids, including (S )-(-)-perillyl alcohol, (S )-(-)-perillaldehyde, geraniol, (R)-(+)-limonene, trans-β-ocimene and 1,8-cineol. In this study, the chemical composition and repellency of essential oils of the plant seedlings collected from West Pokot (35◦E, 1◦N) and propagated in seven different geographical regions of Kenya [West Pokot (35◦E, 1◦N), Kilome (37◦E, 1◦S), Naivasha (36◦E, 0◦), Webuye (34◦E, 1◦N), Nyakach (34◦E, 0◦), Kericho (35◦E, 0◦) and Nairobi (36◦E, 1◦S)] were compared. There were significant variations (P <0.01, 95% CL) in the relative proportions of the six constituents and this was reflected in the repellency of the essential oils (P <0.01, 95% CL). Higher repellency of the oil was associated with greater proportions of (S )-(-) perillyl alcohol, (S )-(-)-perillaldehyde and geraniol, and lower repellency was associated with an increased proportion of (R)-(+)-limonene. The results suggest significant epigenetic (chemotypic) variations in the repellency and composition of C. newii essential oils growing in different regions of Kenya.
Combustion synthesis, characterization and luminescence properties of barium aluminate phosphor
(Elsevier, 2014-09) Wako, Ali Halake; Dejene, F. B.; Swart, H.C.
The blue-green emitting Eu2+ and Nd3+ doped polycrystalline barium aluminate (BaAl2O4:Eu2+,Nd3+) phosphor, was prepared by a solution-combustion method at 500 °C without a post-annealing process. The characteristic variation in the structural and luminescence properties of the as-prepared samples was evaluated with regards to a change in the Ba/Al molar ratio from 0.1:1 to 1.4:1. The morphologies and the phase structures of the products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), while the optical properties were investigated using ultra-violet (UV) and photoluminescence (PL) spectroscopy, respectively. The XRD and TEM results revealed that the average crystallite size of the BaAl2O4:Eu2+,Nd3+ phosphor was about 70 nm. The broad-band UV-excited luminescence of the phosphors was observed at λmax=500 nm due to transitions from the 4f65d1 to the 4f7 configuration of the Eu2+ ion. The PL results indicated that the main peaks in the emission and excitation spectrum of phosphor particles slightly shifted to the short wavelength due to the changes in the crystal field due to the structure changes caused by the variation in the quantity of the Ba ions in the host lattice.
Concentration of Laterites Using Biomass
(Kenya Industrial Property Institute, 2015-06-11) Wachira, Jackson M.; Muriithi, Naftali; Waithaka, Peter; Wanjau, Ruth
A method of concentrating iron in laterites to make the iron extraction process economical is disclosed. Concentration using biomass yields higher levels of iron by using appropriate ratio of biomass: laterites. The concentration of iron in the laterites was done by heating a laterite/charcoal mixture in the temperature range 500-700oC in a ceramic container, a slow current of air (0.5- 0.7cm3/sec) was passed thus generating carbon monoxide in-situ. The process involves cooling and picking iron containing mineral. The optimum ratio of biomass: laterite was found to be 1:20 by mass. The iron in the raw laterites is predominantly minerals goethite, FeO.OH and haematite, Fe203, as shown by presence of peaks at diffraction angles of 20 = 21.51 ° and 20 = 54.11 °respectively. After magnetseparation iron was present predominantly as the mineral, magnetite Fe304, with diffraction peak at 20 = 36°. The percentage of iron in the magnet-separated product is increased to 55-62%.
Copper extraction by wet chemical method
(Elsevier, 2018-07) Mutembei, Peterson K.; Wachira, Jackson M.; Mwangi, Isaac; Njoroge, Peter
In many countries large deposits of copper with no locally established copper based industries occur because known methods for extraction are prohibitively expensive and unaffordable. This study reports on an affordable and sustainable method for the extraction of copper. This was achieved through the use of a wet chemical method which makes use of hydrazones prepared in situ from chicken dung leached solution. The method involves the reduction of copper (II) ions leached from copper ore to zero valence using chlorine treated solution prepared from chicken droppings at a temperature range of 60–70 °C. The ore samples were pulverized to 250 micro millimetres and leached with hydrochloric acid to obtain leachate containing copper ions. The dissolved copper was reduced to copper metal and obtained by filtration. It was confirmed by XRFS analysis that, the metal purity was found to range between 60 and 80% depending on the ore used. In another experiment, chicken waste solution was used to extract copper from the ore. To the mixture, chlorine gas was then bubbledthrough a glass delivery tube to prepare the hydrazone in situ at a temperature range of 60–70 °C and a pure copper metal was obtained. The findings from this study have shown that there is great potential for the production of copper at low cost and this could be applied in both small-scale cottage industries and large industries using readily available resources such as chicken dung.
Copper extraction by wet chemical method
(Elsevier, 2018-07) Kugeria, Peterson M.; Mwangi, Isaac; Wachira, Jackson M.; Njoroge, Peter
In many countries large deposits of copper with no locally established copper based industries occur because known methods for extraction are prohibitively expensive and unaffordable. This study reports on an affordable and sustainable method for the extraction of copper. This was achieved through the use of a wet chemical method which makes use of hydrazones prepared in situ from chicken dung leached solution. The method involves the reduction of copper (II) ions leached from copper ore to zero valence using chlorine treated solution prepared from chicken droppings at a temperature range of 60–70 °C. The ore samples were pulverized to 250 micro millimetres and leached with hydrochloric acid to obtain leachate containing copper ions. The dissolved copper was reduced to copper metal and obtained by filtration. It was confirmed by XRFS analysis that, the metal purity was found to range between 60 and 80% depending on the ore used. In another experiment, chicken waste solution was used to extract copper from the ore. To the mixture, chlorine gas was then bubbledthrough a glass delivery tube to prepare the hydrazone in situ at a temperature range of 60–70 °C and a pure copper metal was obtained. The findings from this study have shown that there is great potential for the production of copper at low cost and this could be applied in both small-scale cottage industries and large industries using readily available resources such as chicken dung.
Crop residues used as lignocellulose materials for particleboards formulation
(Heliyon, 2020-09) Kariuki, Stephen W.; Wachira, Jackson M.; Kawira, Millien; Murithi, Genson L.
Efforts to reduce pressure on use of wood in particleboard formulation have included the use of non-wood materials such as crop residues. Physical and mechanical properties are determined by the number of the hydroxyl (-OH) groups. Hydroxyl (-OH) groups attracts water molecules through hydrogen bonding affecting water absorption (WA) and thickness swelling (TS). WA and TS affect curing process of adhesive. Curing process of adhesives affects the mechanical characteristics of formulated particleboards. These challenges have been acted upon continuously through research. This review paper presents crop residues used as alternative lignocellulose material source in particleboard formulation and the various advances that have been made to improve on the properties of the resultant particleboards. Improvement over time of the non-wood material in composite materials focusses on increasing water resistance and compatibility between lignocellulose and binder. Crop residues-based are used in making medium and low density particleboards. These boards have shown good mechanical characteristics which include modulus of rupture (MOR), modulus of elasticity (MOE) and internal bonding (IB). MOR, MOE and IB have over time been improved by enhancing chemical compatibility of lignocellulose material and the binders. Water absorption and thickness swelling remain challenge. This review paper further explored various methods of improving water absorption and thickness swelling of crop-residue based particleboards
Determination of Potassium Levels in Intensive Subsistence Agricultural Soils in Nyamira County, Kenya
(2013) Kenyanya, Omanga; Wachira, Jackson M.; Mbuvi, Harun
Assessment of potassium levels in agricultural soils of Nyamira County, Kenya was necessitated by the observed progressive drops in maize acreage yields over the years despite use of phosphorus and nitrogenous fertilizers. In the study, concentration levels of potassium and other soil fertility indices such as, organic carbon, cation exchange capacity, exchangeable cations, soil pH, available nitrogen, total and available phosphorus were determined. Five composite soil samples were collected at depths of between 0-30 cm from five farms that have consistently been under intensive cultivation. Fractionation of potassium was achieved by sequential extraction of soil sampleswith distilled water, ammonium acetate and nitric acid in that order. Concentration levels of potassium in the extracts were determined using a flame photometer. Potassium concentration levels obtained from the water soluble soil extracts were used to calculate thermodynamic parameters such as free energy of replacement, potassium activity ratio and ionic strength of the soil solution. The relationship between the adsorbed and equilibrium potassium concentration, quantity/intensity was determined by plotting Freundlich adsorption isotherms. The isotherm was used to determine the buffering capacity ofpotassium and the concentration levels of potassium adsorbed on un-specific sites in the soil. The suitability of the adsorption equation was determined by applying the least square regression analysis. From the study available potassium in the soils ranged from 57 to 70 mg/kg and had amean value of 60±5.54.2 mg/kg (ammonium acetate method). The water soluble potassium ranged from 1.8 to 2.2 mg/kg with a mean of 2.02±0.16 mg/kg. Nitric acid extracted potassium had a mean of 149.±2.306 mg/kg. The mean free energy of replacement, Δ𝐹𝐹, was found to be −3572±44.98 cal/mol indicating that the soils have low supplying power of potassium. The potassium buffering capacity of the soils was found to have a mean of 1.189±0.06 mg/kg. The amount of potassium adsorbed on un-specific sites of the soilshad a mean value of 6.993±2.378 L/kg. These findingsreveal the extent of potassium depletionin the soils of this region and will form a baseline for working acreage potassium doses required for remediation.
Diffusivity of Chloride Ion in Mortar Cubes Made Using Ordinary Portland and Portland Pozzolana Cements
(2014) Wachira, Jackson M.; Mutitu, D.K.; Karanja, J.K.
Cement is subject to degradation by aggressive media. This study investigated chloride diffusivity in mortar made from Kenyan cements which included three brands of Ordinary Portland Cements (OPC) and three brands of Portland Pozzolana Cements (PPC) sampled within Kenyan markets. The test cements were used to make mortar prisms at different water/cement ratios. Compressive strength was determined at the 7th and 28th day of curing. The mortars were subjected to laboratory prepared 3.5 % by mass of sodium chloride solution under accelerated ion migration test method for a period of thirty six hours using a 12V DC power source. The compressive strength before subjecting to aggressive media was found to increase with curing duration as well as on decreasing w/c. Compressive strength at all w/c ratios was found to increase after the aggressive media ingress. After subjecting the mortar cubes to Cl- media, they were sliced and the cores from the slices analyzed for Cl- content. From these results, Dapp was approximated from solutions to Fick’s 2nd law using the error function. PPC at all w/c ratios showed lower Dapp than OPC. Cl- ingress for both cement types across all cement categories, increased with the increase in w/c ratio.
Diffusivity of Sulphate Ion in Selected Ordinary Portland and Portland Pozzolana Cements Mortar
(Kenya Chemical Society, 2014) Wachira, Jackson M.; Mutitu, D.K.; Karanja, J.K.
Cement is subject to degradation by aggressive media. This study investigated sulphate diffusivity in mortar made from selected Kenyan cements which included three brands of Ordinary Portland Cements (OPC) and three brands of Portland Pozzolana Cements (PPC) sampled within Kenyan markets. The test cements were used to make mortar prisms at different water/cement ratios. Compressive strength was determined at the 7th and 28th day of curing. The mortars were subjected to laboratory prepared 3.5 % by mass of sodium sulphate solution under accelerated ion migration test method for a period of thirty six hours using a 12V DC power source. The compressive strength before subjecting to aggressive media was found to increase with curing duration as well as on decreasing w/c. Compressive strength at all w/c ratios was found to increase after the aggressive media ingress, however, prolonged exposure or exposure to high levels of sulphate is known to be deleterious to cement/concrete. After subjecting the mortar cubes to SO4 2- media, they were sliced and the cores from the slices analyzed for SO4 2- content. From these results, apparent diffusion coefficient, Dapp, was approximated from solutions to Fick’s 2nd law using the error function. PPC at all w/c ratios showed lower Dapp than OPC. SO4 2- ingress for both cement types across all cement categories, increased with the increase in w/c ratio. Chemical analysis results showed that the Kenyan Cement meet the minimum chemical and phase requirements.
Effect of Bacillus cohnii on Some Physicomechanical and Microstructural Properties of Ordinary Portland Cement
(Hindawi, 2020-09) Ngari, Reginah Wangui; Thiong’o, Joseph K.; Wachira, Jackson M.
Cement-made materials face durability and sustainability challenges. (is is majorly caused by the presence of cracks. Cracking affects the mechanical strength of cement-based materials. Microbiologically induced calcite precipitation (MICP) has been found to enhance compressive strength, thus enhancing on the mechanical and durability properties of these materials. (is paper presents the findings of a study conducted to investigate the effect of Bacillus cohnii on compressive strength development of OPC mortar prisms and the effect of Bacillus cohnii on cement setting time and soundness. Microbial concentration of 1.0 ×107 cells·ml−1 was used. Compressive strength tests analyses were carried out for each category of mortar prisms. Compressive strength tests were carried out on the 2nd, 7th, 14th, 28th, 56th, and 90th day of curing in distilled water and microbial solutions. All microbial mortars exhibited a greater compressive strength compared to the control with the highest observed at 90 days. Highest percentage gain in compressive strength was observed at 90 days which is 28.3%. Microstructural analysis was carried out using a scanning electron microscope (SEM) after 28 days of curing. (e results indicated the presence of calcium carbonate and more calcium silicate hydrate (CSH) deposits on the bacterial mortars. (e bacteria did not have an effect on cement soundness. Setting time was significantly accelerated.

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