Kind Of Fly Ash Research Articles

Performance of Cement Paste with Denitrified Fly Ash Containing NH4HSO4.

The denitrification process was completed in coal-fired power plants, resulting in the fly ash containing NH4HSO4. When this kind of fly ash with ammonia was applied to cement and concrete, there could be phenomena such as a retarded setting time, decreased compressive strength, and volume expansion. This paper mainly investigated the influence of fly ash containing NH4HSO4 on the properties of fly ash cement paste, and pastes with NaHSO4 were set as the control samples. The research on Na+ in cement hydration was studied. The influence of NH4HSO4 content in fly ash on the properties of fly ash cement paste was also investigated. It was found that NH4+ could greatly affect the properties of fly ash cement paste, such as significantly reducing the fluidity, prolonging the setting time, decreasing the compressive strength, increasing the drying shrinkage, decreasing the total heat released during the hydration, and affecting the content of calcium hydroxide hydrate. Increasing the ammonia content of the denitrified fly ash would reduce fluidity, retard its setting time, increase the porosity of the cement stone, and increase the number of pores with large sizes in the fly ash cement paste. The increase of porosity and pores with large sizes in cement decreases the compressive strength and increases the drying shrinkage of the fly ash cement paste.

Reaction Behavior and Influencing Mechanisms of Different Fly Ashes on the NO Removal by Using the Ultraviolet Irradiating Chlorite Method.

Our previous work had demonstrated that UV/NaClO2 was the best advanced oxidation method in terms of nitric oxide (NO) removal, but we have not studied the impact of the fly ash on NO removal under such conditions. For this, this paper selected six kinds of fly ashes and studied their effects on NO removal. The micromorphology, elemental composition, and the elemental oxidation states of these six fly ashes were characterized by scanning electron microscopy-energy-dispersive X-ray spectra, X-ray photoelectron spectroscopy, and inductively coupled plasma methods. The main inorganic components in the six fly ashes are metal oxides (Fe2O3/Fe3O4, SiO2, Al2O3, ZnO, MgO, and TiO2), carbonates (Na2CO3 and CaCO3), and chlorides (NaCl, KCl, and MgCl2). The experimental results suggested that high solubility was the premise condition for the fly ashes exhibiting an inhibitory effect on NO removal. Among all of the metal compounds, Fe2O3/Fe3O4 exhibited the highest inhibitory contribution rate to the NO removal (22.9–45.7%). The anions of Cl– and CO32– acted as scavengers for the free radicals which greatly impaired the oxidation of NO. Based on the simulation experimental results and the UV–vis analysis, the order of inhibitory contribution rates of various metal compounds to the NO removal was determined as Fe2O3/Fe3O4 > TiO2 ≈ Na2CO3 > Al2O3 ≈ ZnO ≈ MnO2 > CaCO3 > NaCl > KCl ≈ SiO2 ≈ MgCl2.

High Performance of Fly Ash Derived Li <sub>4</sub>SiO<sub>4</sub>-Based Sorbents for High Temperature CO<sub>2</sub> Capture

It is urgent to develop excellent solid CO2 sorbents with higher sorption capacity, simpler synthetic process, better thermal stability and lower costs of synthesis in CO2 capture and storage technologies. In this work, a number of Li4SiO4-based sorbents synthesized by lithium carbonate with three different kinds of fly ashes in various molar ratios were developed. The results indicate that the Li2CO3:SiO2 mole ratio used in the sorbents synthesis significantly affects the CO2 absorption properties. The sorption capacity increased with the excess of Li2CO3 first and then decreased when the excessive quantity was beyond a certain amount. The experiments found that FA-Li4SiO4_0.6, CFA-Li4SiO4_0.4, HCl/CFA-Li4SiO4_0.3 presented the best sorption ability among these fly ash derived Li4SiO4 samples, and the corresponding weight gain was 28.2 wt%, 25.1 wt% and 32.5 wt%, respectively. The three sorbents with the optimal molar ratio were characterized using various morphological characterization techniques and evaluated by thermogravimetric analysis for their capacity to chemisorb CO2 at 450&degC - 650&degC, diluted CO2 (10%, 20%) and in presence of water vapor (12%). The adsorption curve of FA- Li4SiO4_0.6 at different temperatures was simulated with the Jander-Zhang model to explore the influence of carbon dioxide diffusion on adsorption reaction. Further experiments showed that the adsorbent had a good sorption capacity in a lower partial pressure of CO2 and the presence of steam enhanced the mobility of Li+. What’s more, FA-Li4SiO4_0.6, CFA-Li4SiO4_0.4 and HCl/CFA-Li4SiO4_0.3 particles showed satisfactory sorption capacity in fixed-bed reactor and excellent cyclic sorption stability during 10 sorption/ desorption cycles.

Influence of fly-ash on the engineering characteristics of stabilised clay soil

Soil must be able to withstand the load and transfer it to ground within the range of allowable deformations, for which it must possess good physical and geotechnical properties. Clay soils become more adhesive once when it becomes wet and whereas if it is dry it is characterised by surface cracks. To overcome these circumstances in soil, it should be treated and stabilized in best way. In this study, the influence of two different kinds of Fly-Ashes namely, Class-F Fly-Ash and Class-C Fly-Ash along with the inclusion of lime in the improvisation of stability characteristics of clayey soil. Experiments were conducted to determine the Atterberg limits, Standard Proctor Compaction values and Un-Confined Compression strength of various soil samples with different mix ratios to evaluate influence of Fly-Ash in the stabilisation process. Addressing to the fact that Fly-Ash does not possess any plastic property, the Clay-Fly-Ash mixes show a decrease in Plasticity Index (P.I.) value with increase in the Fly-Ash content. Fly-Ash addition in the clay soil mix that contains lime decreases the plasticity of soil, and also escalates the workability. The workability is increased by modifications in its particle size and collision behaviour. It is concluded that, the addition of lime and Fly-Ash influenced to acquire to stronger and stiffer soil matrix by reducing the inter particle spacing. Based on the experimental study results, the addition of C-Class Fly-Ash was found to be more effective than F-Class Fly-Ash when supplemented along with lime.

The effects of fineness level of fly ash and accelerator on the setting time and the compressive strength of geopolymer mortar

This experimental study is part of fly ash based geopolymer research development. The type F fly ash which is the quite abundant by-product materials from power plant burning coal in Tanjung Enim, South Sumatera was the background of this research. However, this kind of fly ash was being treated before it would be used. As known that the mechanical properties of the harden of cementitious material is affected by its fineness of the binder material. The beginning researches about this fly ash based geopolymer concluded that early harden process was being difficult. By this problem, in this research some of accelerator/fly ash ratios are used as the one of the variables. This study aimed to determine the contribution of the fineness level of the fly ash as well as the accelerator/flyash ratio to the setting time and its compressive strength of the geopolymer mortar. The sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) as the activator and the accelerator with the 0%, 0.5%, 1%, 1.5% and 2% as the accelerator/fly ash ratios are used in this study. The 3 zones of the fineness level of flyash are being the other variable of the research. The results showed that the fineness level based on fall zone and the accelerator/flyash ratio affect the setting time and compressive strength significantly. The fineness level based on the fall zone increased the compressive strength and tended to produce the shorter setting time. While the higher accelerator/flyash ratio gives the higher compressive strength of geopolymer mortar. The initial setting time and final setting time ranged from 90 minutes to 225 minutes.

Durability of self-compacting concrete made from non-conforming fly ash from coal-fired power plants

The search for answers to the environmental challenges is one of the obligations of the current society. Therefore, the optimisation of natural resources and the minimisation and revaluation of waste should be present in any activity. These purposes should be included in both the construction and energy sectors owing to the large amount of resources consumed and of pollutants and waste generated by them. The present work carries out a feasibility study of the use of fly ash from coal-fired power plants as a filler for self-compacting concrete (SCC). This kind of fly ash does not meet the compliance criteria determined by the regulations, and thus, it is non-conforming fly ash (NCFA). The dual objective of this work is the optimisation of a natural non-renewable resource and the recovery of waste, which should achieve the qualification of end of waste before being used as a by-product. For this purpose, a comparative study of three mixes is performed, namely, SCC-1 with commercial siliceous filler (SF) (SCC reference), SCC-12 with a mix 1:1 by volume of SF and NCFA, and SCC-2 with NCFA. All the mixes showed good self-compactability. The analysis of the relevant parameters, i.e., apparent and dry density, open porosity, mercury intrusion porosimetry, absorption of water by immersion, and capillarity, has been significant to know in depth the durability of the mixes. The results show that it is possible to obtain a SCC with high performance with respect to durability, attack of aggressive agents, and shrinkage by replacing the SF of siliceous nature with NCFA.

Comparative investigations of influence of chemical admixtures on pozzolanic and hydraulic activities of fly ash with the use of thermal analysis and infrared spectroscopy

The aim of this work is to investigate the influence of selected alkaline activators on pozzolanic and hydraulic activities of fly ashes using thermal analysis (TG/DTG) and infrared spectroscopy (FTIR). Two types of fly ashes differing in chemical compositions, especially content of calcium components, were selected for investigations. The study was carried out for two types of samples: (1) fly ash–lime paste performed with low-calcium fly ash and (2) a paste performed with high-calcium fly ash and water without introduction of additional amount of Ca(OH)2. Chemical admixtures NaOH, Na2SO4, and Na2CO3 were added to both the types of samples. It was confirmed that influence of chemical activators on pozzolanic and hydraulic properties of fly ashes strictly depends on the kind of fly ash and availability of Ca(OH)2. For example, in case of high-calcium fly ash, the most active action was exhibited by NaOH solution.

Effect of Mechanical Activation on Properties of Alkali Activated Binders

Effect of mechanical activation of fly ashes on strength of alkali activated binders is investigated. Four different kinds of fly ashes are mechanically activated. The aim of mechanical activation is to increase the reactivity of fly ashes. Mechanically activated fly ash is used as an admixture to the untreated original fly ash in proportion of 0, 50, 75 and 100 %. Fly ashes are alkali activated with solutions containing sodium hydroxide and sodium water glass. Compressive and flexural strength is tested on hardened alkali activated binders.

Pozzolanic and hydraulic activity of calcareous fly ash

Usefulness of domestic calcareous fly ashes as pozzolanic and hydraulic constituents of cements and hydraulic binders is a subject of this paper. Test results of standard properties, activity indices of calcareous fly ashes and physical and mechanical properties of cements with this kind of fly ash are presented. Factors which might exerted an influence on hydration and hardening processes of cements with calcareous fly ashes form Bełchatow Power Station were analyzed. Beneficial results of calcareous fly ash activity were discussed regarding phase composition and morphology. The function of glassy phase in hydration and hardening processes of fly ashes as well as cements and binders with this constituent was emphasized.

Potassium Solubility of the Fly Ash from Corn Straw Power Plant

The industry of biomass power in China has been growing tremendously in recent years, but it is faced with many challenges now. The low efficiency of straw combustion in the boiler results in that the carbon content in the fly ash could reach 15~30%. The ash is also rich in silica, potassium, calcium and has a lot of microelements. A kind of fly ash from a biomass power plant mainly uses corn straw as feedstock was studied. XRF analysis showed that the contents of K2O, CaO and MgO in the ash were 7.22%, 13.61% and 7.22%, respectively. Leaching experiments were conducted to evaluate the solubility of nutritive elements K, Ca and Mg in the ash. The results indicated that acid could enhance the solubility compared with pure water. Under the optimal conditions of filtrate final pH neutral, leaching time 20min, ratio of liquid to solid (L/S) 2, reaction temperature 40°C and stirring time 1min just for homogenization, 36.9% of K, 42.8% of Ca and 10.1% of Mg in the ash could be extracted. These dissolution rates were still very low, that means, the thorough extraction is not very easy and further research should be continued to make the straw power industry ecological and sustainable.

Kinetic and equilibrium studies on the adsorption of calcium lignosulfonate from aqueous solution by coal fly ash

Experiments were performed to determine the adsorption of calcium lignosulfonate (CLS) onto Shand and Boundary Dam (BD) coal fly ashes. The results showed that both Shand and BD fly ashes exhibited potential for CLS adsorption. The removal efficiency increased with increasing adsorbent dosage and the maximum was obtained in the dosage of 20g/L. Adsorption processes were time-dependent and the maximum adsorption capacity was achieved in the contact time of 120min. Also, the processes were temperature-dependent and the maximum adsorption capacity was obtained at 20°C. Additionally, adsorption of CLS could well fit the Pseudo-second-order kinetic model and the isotherm experimental data were correlated well with the Freundlich and Langmuir equations. Thermodynamic studies suggested that the adsorption of CLS onto both kinds of fly ashes was exothermic, the thermodynamic parameters were as follows: ΔG (4.56, 5.06kJ/mol), ΔH (−15.58, 12.12kJ/mol), ΔS (−0.0688, −0.0588kJ/(molK)) for Shand and BD fly ashes, respectively. Adsorption efficiency decreased with increasing pH over the range pH 2–8 and there was a slight increase as pH further increased. The maximum was obtained in pH 2–3. Also, the adsorption behaviors of CLS onto fly ash could be influenced by the ionic strength and the maximum was obtained in NaCl concentration of 0.1mol/L. The results will have significant implications for the treatment of complex pulp and paper effluent by adsorption on low-cost adsorbents.

Direct speciation of lead, zinc and antimony in fly ash from waste treatment facilities by XAFS spectroscopy

It is important to understand the chemical states of heavy metals in solid waste from municipal incinerator (MSWI) fly ash as both the toxicity and behavior in the environment of heavy metals differ with their chemical states. In this study, direct speciation of lead, antimony and zinc in MSWI fly ash was conducted by XAFS spectroscopy. Three kinds of fly ash from continuous stoker-type MSWIs and a kind of fly ash from an ash melting plant (AMP) were investigated. XAFS measurements were carried out on beam line BL01B1 at SPring-8. The lead, zinc and antimony spectra were collected in fluorescence detection mode at room temperature with a Si (111) or Si (311) monochromator. According to Pb LIII-edge XANES spectra, lead was estimated to be predominantly PbCl2 in MSWI fly ashes and PbO in AMP fly ash. Zinc was estimated to be speciated predominantly as ZnCl2 in MSWI fly ashes and a mixture of 2ZnCO3·Zn(OH)2, ZnO and ZnS in AMP fly ash. Antimony K-edge XANES spectra indicated that Sb is five-valent in all the fly ashes.

高炉セメントB種にフライアッシュを用いた高流動コンクリートの流動特性およびコンクリートの品質に関する研究

This paper is intended to study the effects of the mix proportion on the Theological figures, strength and shrinkage ratio of the high-fluidity concrete sing portland blast-furnace slag cement and fly ash. The relationship between the mix proportion and the fluidity etc. of the concrete was investigated regarding several experimental factors such as kind of fly ash, mixing ratio of fly ash to portland blast-furnace slag cement, mixing ratio of super plasticizer, and so on. The Theological characteristics of the high-fluidity concrete such as plastic viscosity and yield value were measured by using the J shaped flow test. The main results on the fluidity are as follows. 1) In case of increasing the mixing ratio of Type I fly ash and Type II fly ash, the plastic viscosity and the yield value decrease. 2) The plastic viscosity and the yield value of the concrete which mixed Type II fly ash to 15% are smaller than those of the concrete using-portland blast-furnace slag cement with little addition quantity of super plasticizer.

Activation of the fly ash pozzolanic reaction by hydrothermal conditions

The effect of hydrothermal treatment on the pozzolanic reaction of two kinds of Spanish fly ashes from coal combustion (ASTM class F) is discussed. Characterization of the compounds formed as a result of hydrothermal treatment and the changes provoked in the starting fly ashes were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared (IR) spectroscopy. α-C 2SH, CSH gel, different solid solutions of katoites (the cubic crystallographic variety of hydrogarnets series (C 3ASH 4)) and a mixed oxide (CaFe 2O 4) were formed depending on the kind of fly ash. The hydrated compounds are precursors of a new kind of low-energy cement called fly ash belite cement (FABC); besides, they have potential properties to intercalate toxic ions and therefore can be used as immobilization systems of these ions.

フライアッシュを使用した高流動コンクリートの調合要因が流動特性に及ぼす効果

This paper is intended to study the effects of the mix proportion on the theological figures of the high-fluidity concrete using fly ash. The relationship between the mix proportion and the fluidity of the concrete was investigated regarding several experimental factors such as the kind of fly ash, the mixing ratio of fly ash to the normal cement, the mixing ratio of super plasticizer and viscosity agent, and sand aggregate ratio, etc. The rheological characteristics of the high-fluidity concrete such as plastic viscosity and yield value were measured by using the J shaped flow test. The main results are as follows. 1) In case of increasing the mixing ratio of Type I fly ash and Type II fly ash, the plastic viscosity and the yield value decrease. In case of increasing the mixing ratio of Type IV fly ash, these values increase. 2) The plastic viscosity of the concrete using Type I fly ash is smaller than that of the concrete using Type II fly ash. 3) The yield value of the concrete using Type I fly ash is nearly the same as that of the concrete using Type II fly ash.

De novo synthesis of polychlorinated dibenzo-p-dioxins and dibenzofurans on fly ash from a sintering process.

Fly ash, collected in the electrostatic precipitator of a sinter plant in Belgium, has been examined and characterized in terms of its behavior with respect to thermal polychlorodibenzo-p-dioxins (PCDD) and polychlorodibenzofurans (PCDF) formation. Thermal experiments of the fly ash were conducted in a flow of air. The temperature was varied from 250 to 450 degrees C, and the reaction time varied from 30 min to 6 h. For comparison, the oxidative degradation of carbon in the fly ash was studied by differential scanning calorimetry (DSC) in the temperature range from 50 to 500 degrees C. Besides the known maximum of formation of PCDD/Fs around 325 degrees C generally found on experiments with incinerator fly ash, a second maximum of formation around 400 degrees C is observed on the sinter fly ash used in this study. DSC measurements on the fly ash show that the oxidative degradation of carbon appears at these two different temperatures confirming that the de novo synthesis on this kind of fly ash take place at two different optimum temperatures. About the reaction time, already after 30 min, an important quantity of PCDD/Fs is formed; the fast increase in PCDD/Fs amount is followed by a slower formation rate between 2 and 4 h. At longer reaction time, the formation slows down, and decomposition reactions become important. Analysis of homologue distribution indicates that the profile of PCDD/Fs is independent of the reaction time but that an increase of the temperature leads to a rise of lower chlorinated species. In all experiments, PCDF are formed preferentially (total PCDF/PCDD ratios larger than 5). The PCDF/PCDD ratio is clearly independent of the reaction time. Concerning the temperature, the apparently better stability of PCDF at high temperature (PCDF/PCDD ratio higher at high temperature) results in the fact of different PCDF/PCDD ratios for the different family and modifications of homologue distribution with the temperature. The isomer distribution shows little reaction time or temperature dependency, which is an argument in favor of a thermodynamic control of the isomer distribution during de novo formation of PCDD/Fs. Differences within the isomer distribution patterns of PCDD/Fs obtained from the laboratory de novo synthesis experiments and the original fly ash, reflecting the formation under the industrial process, suggest a different mechanism of formation in the sinter plant for the PCDD and PCDF. The de novo synthesis is sufficient to explain the PCDF formation in the real process, but synthesis from precursors must play a role for the PCDD formation.

Properties of concrete made with fly ash

This paper presents the results of research to obtain low cost concrete, using industrial by products and waste. The objective is to use these materials in low cost construction with adequate durability and compressive strength. Different cement replacements have been studied by substituting 20%, 40% and 60% cement with two kinds of fly-ashes, in their natural state and after being subjected to a grinding process until a greater ash fineness than that of cement was obtained. Data on the physical and chemical properties of the ashes, workability and compressive strength data of control and fly ash concrete are presented.

The fluidity of fly ash-cement paste with superplasticizer

The influence of various fly ashes on the fluidity of fly ash-cement paste with superplasticizer was investigated in connection with the amounts of superplasticizer adsorbed on fly ashes, the change of ζ-potential and the physical properties of fly ashes. Fly ash indicates a high negative ζ-potential, and by adding superplasticizer, an even higher negative ζ-potential is indicated. However, the fluidity of fly ash paste is not improved by addition of superplasticizer as much as in the case of cement. The fluidity of fly ash-cement paste mixed with superplasticizer is influenced by the kinds of fly ashes. The bulk specific gravity of fly ash may be an index for judging the influence of fly ash on the fluidity of fly ash-cement paste.