Showing papers on "Fly ash published in 1986"

Use of fly ash in concrete

Abstract: This synthesis summarizes available information concerning the use of fly ash in hydraulic-cement concrete, and attempts to establish consensus concerning a number of applications relating to highway construction. Fly ash marketing procedures are briefly reviewed, and the amount of fly ash now being used is summarized. The results are reported of a questionnaire survey of the status of the use of fly ash concrete (FAC) in each state of the U.S. and the provinces of Canada. There is an increase in FAC use since 1980. This trend is aided by the development of a flyash industry. Trends also indicate a developing technology that will be oriented around performance of the hydraulic cement concrete. Currently, most states view the proportioning of of FAC from the standpoint of the amount of portland cement to be replaced by the fly ash and have maximum replacement limits. It has been noted that the same fly ash with different cements may react differently and develop different early and ultimate strengths. The need is emphasized for preliminary tests to establish optimum proportioning of ingredients in the concrete using materials from the sources to be supplied to the job.

Process for forming a light-weight aggregate

Abstract: A process is disclosed for forming lightweight aggregate pellets having a density of less than about 60 lbs./ft. 2 . The first step of the process is to form an admixture which includes fly ash, cement and filler. By weight percent of the admixture formed, the admixture includes greater than 60% fly ash, 1-25% cement and 1-10% filler. Water and a chemical accelerator are added to the admixture in a pelletizing device. By weight percent of the aggregate formed, about 1 to 18% water is added and between about 0 and 3% chemical accelerator is added by weight of the cement used in the admixture. The aggregate pellets are then removed from the pelletizing device and cured with an oxygen containing gas, such as air, at a temperature of less than about 300° F.

Fly ash recycle in dry scrubbing

Abstract: The paper describes effects of fly ash recycle in dry scrubbing. Previous workers have shown that the recycle of product solids improves the utilization of slaked lime--Ca(OH)/sub 2/--for SO/sub 2/ removal by spray dryers with bag filters. In laboratory-scale experiments with a packed-bed reactor, utilization was increased several-fold when the Ca(OH)/sub 2/ was first slurried with one of several different fly ashes. The enhancement increased with the higher loading of fly ash--g fly ash/g Ca(OH)/sub 2/. Much higher Ca(OH)/sub 2/ utilization was achieved when silicic acid was used instead of fly ash. Scanning electron microscopy supports the explanation that Ca(OH)/sub 2/ and silica dissolve and reprecipitate as a more reactive calcium silicate. Other major constituents of fly ash have less or no effect at all on Ca(OH)/sub 2/ utilization. The amount of calcium in the fly ash did not affect the overall SO/sub 2/ removal after Ca(OH)/sub 2/ was added. Slurrying for longer than 2 hours at higher than 60/sup 0/C can improve the utilization of Ca(OH)/sub 2/ slurried with fly ash.

Insulation formed of precipitated silica and fly ash

Abstract: Precipitated silica is mixed with a fly ash material and is employed as an insulating material having a low thermal conductivity. The mixture of precipitated silica and fly ash material is dried, compressed, placed in an evacuable pouch, and evacuated. The resulting board-like insulation configuration is used directly as insulation. The board-like material which is produced may be used as insulation in household refrigerators and freezers by placing it in an insulation space between the inner liner and the outer case and encapsulating the board-like material with a foamed insulating material.

Method for the recovery of minerals and production of by-products from coal ash

Abstract: The method of the present invention is a novel comprehensive process for maximizing the recovery of valuable mineral values from coal ash. Options may also be included for the production of saleable inorganic chemical by-products. The process employs both physical and chemical extraction techniques that maximize the yield of products while reducing the quantity of waste produced. Valuable minerals and chemicals such as cenospheres (hollow microspheres), carbon, magnetite (Fe3 O4), alumina (Al2 O3), iron oxide (Fe2 O3) and iron chloride (FeCl3) may be produced. Due to removal of carbon, magnetite, and iron oxide from the coal ash, the processed ash comprises a quality pozzolan.

Permeability and Pore Structure of Cement Pastes Containing Fly Ash, Slag, and Silica Fume

Abstract: As part of research to develop a highly durable concrete container for radioactive waste disposal in chloride and sulfate bearing granite groundwaters, a variety of cement pastes were studied. A sulfate resisting portlandcement was used with various replacement levels of Class F fly ash and pelletized blast furnace slag at a water to solids ratio (W/S) = 0.36. Blends with fly ash, slag, and silica fume were also combined with a super water reducer at W/S = 0.25. Results are presented for strength development, permeability to water, and pore size distribution after 7, 28, 91, and 182 days moist curing. As a direct measure of durability, after 91 days moist curing, paste prisms were immersed in both de-ionized water and a synthetic chloride and sulfate bearing groundwater at 70°C. While all three supplementary cementing materials (mineral admixtures) reduced ultimate permeabilities, silica fume was more effective in reducing permeability at early ages. Silica fume was also the most effective in reducing calcium hydroxide contents of the pastes while slag was the least effective; only reducing calcium hydroxide levels by dilution of the portland cement. From preliminary analysis, there does not appear to be a way of accurately predicting permeability from porosity or pore size parameters alone.

Morphological and chemical characterization of iron-rich fly ash fractions

Abstract: Fly ash samples collected from the electrostatic precipitator of a coal-fire power plant were separated into relatively magnetic and nonmagnetic fractions. The magnetic portions of these samples were examined by scanning electron microscopy, optical microscopy, and X-ray diffraction. The fly ash particles in the magnetic concentrates were predominately spherical and were generally solid in cross section, although vesicular particles were common in the larger sizes (e.g., >50 ..mu..m). The larger particles also exhibited the most diversity with respect to internal morphology. A variety of dendritic growths were among the features observed. X-ray diffraction analyses revealed that the magnetic fly ash fraction was composed primarily of magnitude and less amounts of hematite. Results of this study suggest a potential for increasing ash density and purity by selecting a particle size range that will optimize these parameters. This in turn could make it more suitable for use as a heavy medium in physical coal beneficiation. 22 references, 9 figures.

Influence of Type of Cement and Curing on Carbonation Progress and Pore Structure of Hydrated Cement Pastes

Abstract: Different series of cement paste specimens were prepared with ordinary Portland cement, with portland, blast furnace slag cements having slag contents of 30, 50 and 75% by mass, with commercial fly ash cement and with portland cement containing fly ash additions of 10, 20, 30 and 50% by mass. Moist curing of the specimens varied between 3 and 28 days before the pore size distribution and characteristics of the phase composition were analyzed. Subsequent to curing, the specimens were subjected to drying in air of 65% RH with a controlled CO2 content of 0, 0.03 and 2% CO2 by volume. Depth of carbonation, pore size distribution of the carbonated paste, and the phase composition were investigated after 28 days and 6 months of drying, respectively. The results show that carbonation alters the prevailing pore structure of the hydrated paste. Important parameters are the type of cement used and the duration of curing.

Influence of carbonaceous particles on the interaction of coal combustion stack ash with organic matter.

Abstract: Stack ash samples were fractionated by aerodynamic size, and the largest particle size fraction was separated into constituent particle type subfractions. Comparison of the mineral, magnetic, and carbonaceous particles showed that coked coal is responsible for the sorptivity of the large particle size fraction for carbon-14 labeled benzo(a)pyrene ((/sup 14/C)BaP) and for low solvent extraction recoveries. Elevated levels of organic matter and surface area also are contributed by the carbonaceous particles. In contrast, solvent extraction recoveries of polar degradation products of (/sup 14/C)BaP are attributable more to the mineral and magnetic particles and to exposure of the ash to light and oxygen. Analysis of bulk ash samples may not fully reflect the true organic composition of stack ash. 27 references, 1 figure, 4 tables.

An Investigation of Factors Affecting the Physical Characteristics of Flyash Formed in a Laboratory Scale Combustor

Abstract: An Australian bituminous coal was burnt in a laboratory drop-tube combustor at 1400, 1500 and 1600°C to determine the effect of p.f. properties and combustion temperature on the character and particle size of the flyash. The experiments showed that the mass mean particle size of the flyash was approximately proportional to that of the p.f., and almost independent of combustion temperature. In contrast, the proportion of fine ash (< 10 μ) was independent of p.f. size but increased markedly with increased combustion temperature. The upper size of the ash was determined by unburnt char for the 175 μm and 240 μm p.f. and by the mineral matter for the 29 μm p.f. Cenosphere formation increased with combustion temperature and dominated the ash formed at 1600°C. The work emphasises the need for more detailed p.f. analysis during laboratory and pilot-scale combustion studies into flyash formation and related phenomena such a's fouling, filtration and precipitability. Additional research is required to qua...