Development and mechanical properties of the pelletized fly ash
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Porous ceramics have a great potential to be utilised for adsorption purposes. In this study, the effects of fly ash addition in porous clay-fly ash composites via polymeric replica technique were investigated. The results shows that the fly ash addition from 1:1 to 1:1.5 (clay:fly ash ratio) have promoted favourable results for compressive strength (0.228-0.284 MPa), porosity (97.0-97.4 percent) and densities (2.358-2.439 g/cm 3 ) respectively. When the fly ash ratio addition was increased up to 1:2 (clay:fly ash ratio), the compressive strength (0.18 MPa) reduced significantly. However, the density was bounced back to 2.404 g/cm 3 at the same ratio. This condition was occurred due to high concentration of mineral contents when fly ash addition has increased. Based on XRD pattern, the intensities between mullite and quartz was reduced when clay:fly ash ratio increased from 1:1 to 1:1.5. As the clay:fly ash ratio was increased up to 1:2, the intensities of mullite and quartz showed an increment in XRD pattern. However, there were only 4 percent of changes in porosity when the fly ash addition was 1:2 (clay: fly ash ratio). The reticulated structures of porous clay-fly ash composites were similar although fly ash addition has increased from 1:1 to 1:2.
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As electricity increases every year in our country,the emissions from coal-fired power plants fly ash also increase and the environmental problem of fly ash is increasingly serious. Due to the use of fly ash much less than the total emissions,new areas of development and utilization of fly ash become a research hotspot. This paper analyzed the composition and morphology of fly ash. And the main application of fly ash were also discussed. The fly ash as adsorbent were used to remove SO2,CO2 and Hg in flue gas. This paper emphasized the present situation of the SCR denitration catalyst,the removal effect of NOxwith fly ash loading with transition metals as low-temperature SCR denitration catalyst and the preparation method of catalyst. Fly ash has been proved to have good removal effect of SO2,CO2,Hg and NOxin many studies. Because of good application of fly ash in flue gas treatment,the future development direction of fly ash to control pollution was propoesd.
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1. Uses of Fly Ash in Cement and Concrete 2. Effect of Fly Ash on the Properties of Fresh Concrete 3. Effect of Fly Ash on the Structural Properties of Hardened Concrete 4. Admixtures in Fly Ash Concrete 5. Miscellaneous Opportunities for Fly Ash Use 6. Fly Ash Usage in Waste Management 7. Special Problems Including Use Constraints 8. Types and Properties of Fly Ash 9. Effect of Fly Ash on the Durability of Concrete 10. Applications of Fly Ash in Special Concretes
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By the experiments of fly ash mortar,the activating effect of five activators of fly ash(Na2SO4,Ca(OH)2,Na2SiO3,CaSO4,the mixture of Na2SO4 and Ca(OH)2) was compared and the impact of low-calcium fly ash and high-calcium fly ash on the mechanical properties of fly ash mortar was also analyzed.For a high volume fly ash part,in order to improve its early strength,high-calcium fly ash should be chosen and CaSO4 or the mixture of Na2SO4 and Ca(OH)2 should be selected as the activator.
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Fly ash is mainly the solid waste emitted by coal-fired fossil fuel power stations, which is collected through the flue gas emitted. At present, the comprehensive utilization of fly ash has been widely promoted and applied in actual production. The application of fly ash to concrete can not only improve the strength of concrete, but also save cement. However, its hydration rate is slow, and the incorporation of concrete will reduce the early strength of concrete. In order to improve the activity and other properties of fly ash, ultrafine fly ash with small particle size is obtained by grinding fly ash. Ultrafine fly ash has finer particle size than fly ash and larger spherical shape than original fly ash. Water demand decreases, density increases and activity increases. It can better fill the cement void, improve the internal compactness of concrete, and improve the interface structure of materials. Research has shown that adding 10% to 20% fly ash can achieve better performance than conventional concrete. For higher fly ash content, the strength decreases with the increase of fly ash content.
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This paper discusses reactivity and high-strength mechanism of modified fly ash concrete by DSC, SEM and DTA. The result indicates the shape effect, activation effect and micro-aggregate effect of the modified fly ash is developed sufficiently. The reactivity of modified fly ash concrete is enhanced obviously. The binder material of modified fly ash hydration heat is much more than the original fly ash's. The hydration products of concrete which is made with modified fly ash contain much less CH and more C-S-H gel, and the each day strength of concrete is higher and interfacial transition zone of concrete improved obviously. Grains of modified fly ash are smaller, so it can be scattered into cement paste better to make the pores of concrete subdivided and filled.
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Fly ash is one of the most voluminous industrial byproducts that result from coal combustion. This study examines the physical and chemical characteristics of fly ash with the aim of: differentiating between high-Ca fly ash with low Ca ash, and exploring the statistical variability of fly ash properties. The paper describes the results of the laboratory tests used to evaluate the cementing characteristics of Class C fly ash obtained from power plant burning subbituminous Wyoming coal. Laboratory tests demonstrate that fly ash can be effectively used as cement surrogates in portland cement concrete, for intermediate strength fly ash concrete or flowable fills, and for low strength clay soil stabilizer.
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Current US national standards for using fly ash in concrete (ASTM C618) state that fly ash must come from coal combustion, thus precluding biomass-coal co-firing fly ash. The co-fired ash comes from a large and increasing fraction of US power plants due to rapid increases in co-firing opportunity fuels with coal. The fly ashes include coal fly ash, wood fly ash from pure wood combustion, biomass and coal co-fired fly ash SW1 and SW2. Also wood fly ash is blended with Class C or Class F to produce Wood C and Wood E. Concrete samples were prepared with fly ash replacing cement by 25%. All fly ash mixes except wood have a lower water demand than the pure cement mix. Fly ashes, either from coal or non coal combustion, increase the required air entraining agent (AEA) to meet the design specification of the mixes. If AEA is added arbitrarily without considering the amount or existence of fly ash results could lead to air content in concrete that is either too low or too high. Biomass fly ash does not impact concrete setting behaviour disproportionately. Switch grass-coal co-fired fly ash and blended wood fly ash generally lie within the range ofmore » pure coal fly ash strength. The 56 day flexure strength of all the fly ash mixes is comparable to that of the pure cement mix. The flexure strength from the coal-biomass co-fired fly ash does not differ much from pure coal fly ash. All fly ash concrete mixes exhibit lower chloride permeability than the pure cement mixes. In conclusion biomass coal co-fired fly ash perform similarly to coal fly ash in fresh and hardened concrete. As a result, there is no reason to exclude biomass-coal co-fired fly ash in concrete.« less
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A quantitative understanding of the efficiency of fly ash as a mineral admixture in cement-based materials is essential for its effective utilisation. The present paper is directed towards a specific understanding of the efficiency of fly ash in cementitious materials systems by considering the independency of fly ash and its dependency on the characteristics of the cementitious materials system. A new method of quantitatively evaluating the strength effect of fly ash is proposed, in which two parameters, the strength-effect index and the strengthening factor, are employed to study strength development in fly ash mortars and concretes and to further analyse the influences of water to binder ratio (w/b) and the replacement amount of fly ash on strength. Results indicate that the strength effect of fly ash in mortar systems is different from that in concrete; the strength effect of fly ash varies with both amount of fly ash and w/b. Furthermore, in a concrete system, two different optimal w/b ratios are used to maximise the strength-effect index and the strengthening factor of fly ash, respectively. An optimum amount of fly ash exists for an optimal unit strength-effect index in concrete. It is shown that the method presented in this paper is reasonable and effective in assessing the efficiency of fly ash. This information will strengthen the effective utilisation of fly ash in cementitious materials and design of fly ash concrete.
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