Presence Of Fly Ash Research Articles

Thermal And Frequency Dependance Dielectric Properties Of Conducting Polymer/ Fly Ash Composites

With more than 100 million tonnes of fly ash produced in India, use of fly ash for the preparation of polyaniline – fly ash composites will in no way help in its bulk utilization. Still the authors have made an effort towards the better utility of fly ash by synthesizing polyaniline –fly ash composites for electronic devices where the requirement of dielectric materials with good electrical conductivity. There is great challenge to use the waste of thermal power stations in the form of fly ash as reinforcement for the conducting polymers to be good dielectric materials. In this paper, we report the use of fly ash to prepare conducting polymer composite materials. In-situ polymerization of aniline was carried out in the presence of fly ash (FA) to synthesize conducting polyaniline–fly ash composites (PANI-FA) by chemical oxidation method. The PANI-FA composites have been synthesized with various compositions (10, 20, 30, 40 and 50 wt %) of fly ash in conducting polymer matrix. The surface morphology of these composites was studied by scanning electron microscopy (SEM). These composites were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffractometry (XRD), Fourier Transform Infra-Red (FTIR) Spectroscopy to investigate surface morphology and structure of the composites. Thermal and frequency dependence dielectric properties of all the synthesized composites have been studied with the help of impedance analyzer. By incorporating fly ash into conducting polymers, dielectric constant of the composites was found to be improved as compared to that of pure conducting polymers. It was also noticed that the dielectric constant of all the composites found to be decreased with increasing frequency but increased with increasing temperature. The results obtained for these composites are of greater scientific and technological interest for good quality capacitors.

Air void system parameters and frost resistance of air-entrained concrete containing calcareous fly ash

The paper presents results of the investigation of the air void characteristics and the resistance to cyclic freezing and thawing of air-entrained concrete containing calcareous fly ash. The frost resistance was tested also under the presence of de-icing salts to check the resistance to frost-salt scaling and without de-icing salts. The range of investigation included air entrained concrete mixes with the specified water-binder ratio of w/b=0.45 with addition of calcareous fly ash or made using blended cements with calcareous fly ash (W), and also siliceous fly ash (V) and ground granulated blast-furnace slag (S). The coarse aggregates used were crushed granodiorite and crushed limestone. The air-void system parameters were determined by microscopic image analysis and the effect of addition of calcareous fly ash was assessed. The effect of concrete age and presence of fly ash W on the strength and freeze-thaw resistance was also studied. The tests have shown that the use of calcareous fly ash as one of the main constituents of blended cements does not affect the frost salt scaling resistance nor the resistance to internal frost damage provided that the air void system is adequate.

Construction of Roller-Compacted Concrete Pavement in the Fayetteville Shale Play Area, Arkansas

In 2012, roller-compacted concrete (RCC) pavement was used to rehabilitate a deteriorated section of roadway in the Fayetteville Shale Play Area (FSPA), Arkansas. As the result of recent heavy truck traffic related to natural gas exploration efforts in Arkansas, the FSPA has experienced significant pavement distresses that typical maintenance activities cannot sufficiently address. RCC pavement was selected as a potential solution to repair failing pavements in this area because that pavement could be constructed more quickly than conventional concrete pavements and could provide adequate structure for truck traffic. Two sections of RCC pavement were constructed on a rural, two-lane highway. The first was a 7-in. section placed on a cement reconstructed base course, and the second was an 8-in. section placed as an overlay. The RCC mixture contained a nominal, maximum aggregate size of ¾ in. and was designed to meet a minimum, 28-day compressive strength of 5,000 psi. Although some difficulties were encountered during the construction process, the final product was considered successful. Low initial strengths in Section 1 were believed to be caused by a combination of low temperatures and the presence of fly ash in the mix. Fly ash was removed from the mix design before the construction of Section 2 began, and the strength characteristics were much improved. Diamond grinding was used to ensure surface smoothness; this treatment resulted in an average International Roughness Index value of 69.5. After 6 months, a distress survey was performed in which minimal cracking was found. Minor surface distresses, including popouts and deterioration at construction joints, were noted.

High temperature oxidation and corrosion of gas turbine materials in burner rig exposures

With the introduction of novel fuels, which may contain high levels of trace impurities including sulphur and alkali metals, industrial gas turbines are operating with increasingly corrosive combustion environments. To investigate the effect that this, coupled with the higher combustion gas temperatures needed to increase power plant efficiency, has on current state-of-the-art gas turbine component materials, three burner rig exposure tests have been run. The tests evaluated the effects of fly ash, gas moisture and gas temperatures on the alkali sulphate induced hot corrosion of CM247LC, Haynes 230, IN939 and IN728LC. Type I (sulphidation and internal damage), type II (pitting) and mixed mode hot corrosion were observed under different test conditions; however, the presence of fly ash appeared to reduce the levels of hot corrosion. CM247LC, with its high Al content improving oxidation resistance, showed less resistance to hot corrosion than the other, higher Cr content, alloys.

Experimental study on strength gaining characteristics of concrete using Portland Composite Cement

This study deals with experimental investigation of strength gaining characteristics of concrete made with Portland Composite Cement (PCC) and Ordinary Portland Cement (OPC). Compressive strength of concrete is often considered as a measure to determine the rate of strength gain of concrete with age and different cement composition. Strength developments of five concrete types have been investigated in terms of cement content and curing duration. Experimental observations on 495 specimens reveal that the early age strength of PCC concrete is lower than that of OPC concrete. Based on the test results, lack of proper pozzolanic reaction in the presence of fly ash in PCC concrete strength is lower at early age. The pozzolanic activity of fly ash also contributes to the strength gain at later stages of continuous curing. This study also concludes that drying ambient conditions reduce the strength potential of PCC concrete as the secondary (pozzolanic) reaction fails to contribute to the development of strength.

Bioleaching of Fly Ash by the Tropical Marine Yeast, Yarrowia lipolytica NCIM 3589

Fly ash collected from an Indian thermal power plant was characterised by scanning electron microscope (SEM)-energy dispersive spectrometer, X-ray diffraction and energy dispersive X-ray fluorescence analysis. The effect of fly ash on the growth and morphology of a metal-tolerant tropical marine yeast, Yarrowia lipolytica NCIM 3589, was studied. The growth of the yeast was unaffected by the presence 0.1, 0.2 or 0.3% fly ash although the surface-to-volume ratio decreased. The yeast formed biofilms on immobilized fly ash as evidenced by SEM observations. The organism produced citric acid and additional extracellular proteins in the presence of fly ash. Leaching of metals from fly ash by Y. lipolytica was compared with chemical leaching by citric acid. Yeast cells were most effective in leaching Cu (59.41%) although other metals (Zn, Ni, Cu and Cr) were also extracted. Transmission electron microscope images showed the deposition of metals at the cell wall, cell membrane and in the cytoplasm. This paper thus reports a potential application of Y. lipolytica for removal of different metals from solid waste material (fly ash).

Mechanical and durability properties of self-compacting concrete containing fly ash and bottom ash

The paper investigates the production of self-compacting concrete (SCC) more affordable for construction industry with various percentages of fly ash as part of the total powder content and bottom ash as replacement of fine aggregates. Various properties studied included strength (compressive and split tensile strength) and durability properties (carbonation and deicing salt surface scaling). Based on the materials used in this study, the SCC was observed to be flowable, cohesive, and developed 28-day compressive strength, approximately in the range of 18–35 MPa. Besides the environmental benefits, there could be some technical and economical advantages as well. As a general result, presence of fly ash and bottom ash affected the durability properties of concrete positively.

Heat evolution during the hydration of Portland cement in the presence of fly ash, calcium hydroxide and super plasticizer

Rate of heat evolution during the hydration of OPC, OPC-20wt% FA, OPC-5wt% CH and OPC-20wt%FA-5wt% CH in the presence of 0.2 and 0.5wt% super plasticizer has been studied at 35 and 45°C with the help of TAM Air isothermal calorimeter for 60h. The results have shown that hydration retarded in the presence of super plasticizer. Higher the concentration of super plasticizer, higher is the retardation. However hydration accelerated with the increase of temperature. Mechanism of hydration is discussed in this manuscript.

Determining ASR characteristics using dilatometer method

Alkali–silica reaction (ASR) is a major durability problem in concrete leading to premature deterioration of different types of concrete structures. Current laboratory tests are largely simulative in nature and yield mainly empirical results, and users state that there is little relationship between the test, the results and actual field performance. A different approach is necessary. This paper is part of a broader research study to assist owners, engineers, and contractors to identify and quantify the potential for concrete pavement deterioration, as a result of ASR. To achieve this objective, a comprehensive study on concrete and mortar mixtures using different types of aggregates of different reactivity was conducted to formulate a reliable and timely testing protocol. A kinetic model was proposed to predict ASR characteristics which were calculated using the system identification method. From test results, it was determined that the proposed testing approach provides direct accountability for various factors affecting ASR, such as aggregate reactivity, calcium concentration, presence of fly ash, and solution alkalinity. Chemistry of the alkali solution validates the laboratory research findings.

Eco-friendly synthesis and antimicrobial activities of some 1-phenyl-3(5-bromothiophen-2-yl)-5-(substituted phenyl)-2-pyrazolines

BackgroundGreen catalyst fly ash: H2SO4 was prepared by mixing fly ash and sulphuric acid. Microwave irradiations are applied for solid phase cyclization of 5-bromo-2-thienyl chalcones and phenyl hydrazine hydrate in the presence of fly ash: H2SO4 yields, 1-phenyl-3(5-bromothiophen-2-yl)-5-(substituted phenyl)-2-pyrazolines. These pyrazolines were characterized by their physical constants and spectral data. The antimicrobial activities of all synthesized pyrazolines have been studied.ResultsScanning electron microscopy (SEM) analysis shows the morphology changes between fly ash and the catalyst fly ash: H2SO4. The SEM photographs with the scale of 1 and 50 μm show the fly-ash particle is corroded by H2SO4 (indicated by arrow mark), and this may be due to dissolution of fly ash by H2SO4. The yields of 1-phenyl-3(5-bromothiophen-2-yl)-5-(substituted phenyl)-2-pyrazolines is more than 75% using this catalyst under microwave heating. All pyrazolines showed moderate activities against antimicrobial strains.ConclusionWe have developed an efficient catalytic method for synthesis of 1-phenyl-3(5-bromothiophen-2-yl)-5-(substituted phenyl)-2-pyrazolines by solid phase cyclization using a solvent-free environmentally greener catalyst fly ash: H2SO4 under microwave irradiation between aryl chalcones and hydrazine hydrate. This reaction protocol offers a simple, economical, environment friendly, non-hazardous, easier work-up procedure, and good yields. All synthesized pyrazoline derivatives showed moderate antimicrobial activities against bacterial and fungal strains.

Optimization process parameters for in-situ synthesis of ammonia by catalytic hydrolysis of urea with fly ash in a batch reactor for safe feedstock in power plants

In this study, catalytic urea hydrolysis for production of ammonia in presence of fly ash, at optimum condition, was investigated in a batch reactor. The single and combined effects of operating parameters such as initial feed concentrations, temperature, fly ash doses, times and stirring speed on the production of ammonia from urea were analyzed using response surface methodology. A 25 full factorial central composite experimental design was employed. Analysis of variance (ANOVA) showed a high coefficient of determination value (R2= 0.963) and satisfactory prediction second order regression model was derived. The optimum production conditions were determined as initial feed concentration 19.9 wt. % of urea, temperature 175°C, fly ash dose 7.5g/L, reaction time 25 min and stirring speed 769 rpm. At optimum conversion conditions, the conversion of urea for production of ammonia was found to be 99.8 %.

Effects of Elevated Temperatures on the Compressive Strength of HFCC

This paper presents the results of elevated temperatures on the compressive of high fly ash content concrete (HFCC). The specimens were prepared with three different replacements of cement by fly ash 30%, 40% and 50% by mass and the residual compressive strength was tested after exposure to elevated temperature 250, 450, 550 and 650°C and room temperature respectively. The results showed that the compressive strength apparently decreased with the elevated temperature increased. The presence of fly ash was effective for improvement of the relative strength, which was the ratio of residual compressive strength after exposure to elevated temperature and ordinary concrete. The relative compressive strength of fly ash concrete was higher than those of ordinary concrete. Based on the experiments results, the alternating simulation formula to determine the relationship among relative strength, elevated temperature and fly ash replacement is developed by using regression of results, which provides the theoretical basis for the evaluation and repair of HFCC after elevated temperature.

Study on Residual Splitting Tensile Strength of HFCC after High Temperature

This paper presents the results of the splitting tensile strength of high fly ash content concrete (HFCC) after high temperature and analysis the degraded rules of the residual splitting strength subjected to high temperature and the replacements of cement by fly ash. The specimens were prepared with three different replacements of cement by fly ash 30%, 40% and 50% by mass and were tested after exposure to high temperature 250, 450, 550 and 650°C and room temperature respectively, compared with ordinary Portland cement concrete. The results showed that the splitting tensile strength sensitively decreased with the high temperature increased. Furthermore, the presence of fly ash was effective for improvement of the relative strength. The relative residual splitting strength of fly ash concrete was higher than those of ordinary Portland cement concrete except 30% fly ash replacement. Based on the experiments results, the alternating simulation formula to determine the relationship among relative residual strength, high temperature and fly ash replacement is developed by using regression of results, which provides the theoretical basis for the evaluation and repair of HFCC after high temperature.

The role of iodine monochloride for the oxidation of elemental mercury

The removal of Hg 0 by the homogenous gas-phase reaction and particle-induced reaction was investigated under various conditions. Iodine monochloride was found to be efficient for Hg 0 oxidation, with the apparent 2nd-order rate constant of about 10.5(±0.3) × 10 −17 cm 3 molecules −1 s −1 and 5.7(±0.3) × 10 −17 cm 3 molecules −1 s −1 at 273 K and 373 K, respectively. The pilot-scale tests showed that the removal of Hg 0 by ICl increased significantly in presence of flyash. It was predicted that over 90% of Hg 0 removal efficiency can be obtained with 0.2 ppmv ICl and 20 g/m 3 flyash in flue gas. Though the reaction between Hg 0 and ICl was by far faster than that of Hg 0/Cl 2, the major product was found to be HgCl 2 rather than HgI 2, which implicated that iodine might partly act as the accelerant in Hg 0 oxidation by facilitating the formation of certain intermediates. The results indicated that using ICl to oxidize elemental mercury in coal-fired flue gas can save the consumption of iodine, and it appeared to be a promising oxidant to enhance the removal of Hg 0.

Oxidation and Stabilization of Elemental Mercury from Coal-Fired Flue Gas by Sulfur Monobromide

Sulfur monobromide (S(2)Br(2)) was employed as a task-specific oxidant to capture and stabilize elemental mercury from coal-fired flue gas. Its performances on the removal of Hg(0) were investigated with respect to the gas-phase reaction and particle-involved reactions. It was found that the gas-phase reaction between Hg(0) and S(2)Br(2) was rapid, and the determined second-rate constant was about 1.2(+/-0.2) x 10(-17)cm(3) molecules(-1) s(-1) at 373 K, which was about 30 times higher than that with sulfur monochloride. The pilot tests showed that the presence of fly ash in flue gas can accelerate the removal of Hg(0) significantly. It was predicted that about 90% of Hg(0) removal efficiency can be obtained with 0.6 ppmv S(2)Br(2) and 30 g/m(3) fly ash in flue gas, and the unburned carbon in fly ash played an important role for Hg(0) removal. The fates of S(2)Br(2) and mercury in the process were evaluated, and the product analysis and leaching tests indicated that mercuric sulfide was the main product of the converted Hg(0) by the direct reaction and consequent series reactions, which is more stable and less toxic than other mercury species. Also, the surplus S(2)Br(2) in flue gas could be captured and neutralized effectively by the alkali components in fly ash or FGD liquor, and its hydrolysis products (elemental sulfur and sulfide) were also helpful to the stabilization of mercury. The result indicated that S(2)Br(2) is a promising oxidant for elemental mercury (Hg(0)) oxidation and stabilization for mercury emission control.

Strength and durability effect of modified zeolite additive on concrete properties

This paper presents an investigation into the effect of a modified zeolite additive (PWC) on strength and durability behaviour of concrete. The additive, a blend of selected alkaloids and zeolite, is commercially available and effectively used in soil stabilization for road construction. However, its influence on behaviour and performance for use in concrete has not been explored. In this research, concrete samples were prepared by incorporating PWC and/or 30% fly ash in the mixes. PWC was used in proportions of 0.6%, 0.8%, and 1.0% of the weight of cement. Concretes of 0.5 water/cementitious ratio were subjected to workability, split tensile strength, compressive strength, oxygen permeability, sorptivity, and porosity tests. Hydration behaviour of the cementitious systems and the pozzolanic effect of PWC additive were studied using differential thermal analysis and thermogravimetric analysis. Results show that PWC is effective in improving concrete strength when used at optimum proportions found to be between 0.6% and 1.0%. Sorptivity property of concrete was improved with use of PWC regardless of its proportion in the mix, while permeability of concrete improved only in the presence of 30% fly ash. PWC was found to be most effective when used in the presence of fly ash.

Bromine Chloride as an Oxidant to Improve Elemental Mercury Removal from Coal-Fired Flue Gas

The equilibria and kinetics of the reaction between bromine (Br(2)) and chlorine (Cl(2)) to form bromine chloride (BrCl) at various temperatures were determined. BrCl was employed to oxidize elemental mercury (Hg(0)) under simulated flue gas conditions. The removal of Hg(0) from the gas phase by a homogeneous gas-phase oxidation reaction and the heterogeneous reactions involving flyash were investigated. The second-order gas phase rate constant was determined to be 2.3(+/-0.2) x 10(-17) cm(3).molecules(-1).s(-1) at 373K. The reaction of Hg(0)/BrCl was significantly accelerated in the presence of flyash, and the estimated Hg(0) removal efficiency in the presence of 0.6 ppmv BrCl and 20 g/m(3) flyash was up to 90%. Unexpectedly, the major product was found to be HgCl(2), rather than HgBr(2), indicating that bromine in part acted as the accelerant in Hg(0) oxidation in BrCl/Br(2)/Cl(2) system by facilitating the formation of intermediates. As a result, bromine consumption is much less than if only bromine gas is utilized alone. These results were helpful not only for understanding the mechanism of Hg(0) removal in coal-fired flue gas but also in any atmosphere in which bromine and chlorine species coexist.

Influence of Fiber Volume Fraction and Fiber Type on Mechanical Properties of FRLACC

This article presents results of an experimental study conducted to investigate the influence of fiber volume fraction, fiber type, and presence of fly ash on mechanical properties of fiber-reinforced, lightweight aggregate, cellular concrete (FRLACC). Steel fibers are added at Vf of 0.5, 1.0, and 1.5%, and 25% of cement weight is replaced with fly ash in the control and FRLACC specimens that had shown the highest compressive strength in our preceding work. With the addition of 0.5% Vf of fibers, the increase in compressive strength of the polypropylene FRLACC specimens is slightly higher than that of the steel FRLACC specimens, whereas decreases in their peak load and modulus of rupture over those of control specimens are observed. The findings of the experimental study also show that the utilization of 25% fly ash is more efficient in improving the mechanical properties of the steel FRLACC specimens than those of the polypropylene FRLACC specimens.

Enhanced Elemental Mercury Removal from Coal-Fired Flue Gas by Sulfur−Chlorine Compounds

Oxidation of Hg(0) with any oxidant or converting itto a particle-bound form can facilitate its removal. Two sulfur-chlorine compounds, sulfur dichloride (SCl2) and sulfur monochloride (S2Cl2), were investigated as oxidants for Hg(0) by gas-phase reaction and by surface-involved reactions in the presence of flyash or activated carbon. The gas-phase reaction between Hg(0) and SCl2 is shown to be more rapid than the gas-phase reaction with chlorine, and the second order rate constant was 9.1 (+/- 0.5) x 10(-18) mL-molecules(-1) x s(-1) at 373 K. The presence of flyash or powdered activated carbon in flue gas can substantially accelerate the reaction. The predicted Hg(0) removal is about 90% with 5 ppm SCl2 or S2Cl2 and 40 g/m3 of flyash in flue gas. The combination of activated carbon and sulfur-chlorine compounds is an effective alternative. We estimate that coinjection of 3-5 ppm of SCl2 (or S2Cl2) with 2-3 Lb/MMacf of untreated Darco-KB is comparable in efficiency to the injection of 2-3 Lb/MMacf Darco-Hg-LH. Extrapolation of kinetic results also indicates that 90% of Hg(0) can be removed if 3 Lb/MMacf of Darco-KB pretreated with 3% of SCl2 or S2Cl2 is used. Mercuric sulfide was identified as one of the principal products of the Hg(0)/SCl2 or Hg(0)/S2Cl2 reactions. Additionally, about 8% of SCl2 or S2Cl2 in aqueous solutions is converted to sulfide ions, which would precipitate mercuric ion from FGD solution.

Biosorption behavior of heavy metals in bioleaching process of MSWI fly ash by Aspergillus niger

In this study, it was considered that the biosorption of heavy metals by biomass might occur during the bioleaching of fly ash. This work is focused on the biosorption behavior of Al, Fe, Pb and Zn by Aspergillus niger during the bioleaching process. The fungal biomass was contacted with heavy metals solution which extracted from fly ash by using gluconic acid as leaching agent. The equilibrium time for biosorption was about 120 min. The biosorption experiment data at initial pH 6.5 was used to fit the biosorption kinetics and isotherm models. The results indicated that the biosorption of Al, Fe and Zn by A. niger biomass were well described by the pseudo-first order kinetic model. The pseudo-second order kinetic model was more suitable for that of Pb. The Langmuir isotherm model could well describe the biosorption of Fe, Pb and Zn while the Freundlich model could well describe the biosorption of Al. Furthermore, the biosorption of metal ions decreased evidently in the presence of fly ash as compared to that in the absence of fly ash. This research showed that although the biomass sorption occurred during the bioleaching process, it did not inhibit the removal of Al, Fe, Pb and Zn evidently from fly ash.