Fly ash, content

The shrinkage of mortars produced from different cements increases with then-strength class (higher fineness) but decreases in the case of cements with mineral additions, particularly at high granulated blastfurnace slag and siliceous fly ash content. 

Table 7.3 Chemical composition of fly ash (contents given in mass %) (analyses of R. Skomorowska)...

The increased resistance to the aggressive environment is an advantageous feature of these materials. It is linked with Ca(OH)2 content lowering in the paste, but primarily to the reduction of larger pores share, that means the permeability decrease. The ion exchange ability decreases and this counteracts the corrosion reactions progress. Obviously, these properties are developing with the fly ash content increase, and in the case of sulphate attack— with CjA content decrease in cement clinker. The apparent diffusion coefficient of Na and Q decrease with siUceous fly ash addition is shown in Fig. 7.23 [139]. 

In Unites States and in Canada, as well as in India in numerous constractions concretes with high fly ash content are used [142]. In Table 7.7 the physical and chemical properties of fly ash, which can be used for concretes production with high fly ash content, are given. 

Fig. 8.10 Strength of mortar with various fly ash content as a function of time (according to [37])...

Wang et al. (1992b) combined ferroaluminate cement with micro-silica and fly ash. Mortars made from such blends with an added superplasticizer attained higher strengths even at fly ash contents of 30 per cent. Remarkably, the flexural/compressive strength ratio of such mortars was exceptionally high, i.e. around 0.2. (Table 4.3). 

Wiens, U., Breier, W., and Schiessel, P. (1995) Influence of high silica fume and high fly ash contents on alkalinity ofpore solution and protection of steel against corrosion. American Concrete Institute SP-153 (Vol. 2), pp. 749-761. 

At low fly ash additions— that is, below 15%—the extent of carbonation in mature fly ash concrete tends to be equal to or lower than that in similar concrete mixes with no ash, in spite of the lower calcium hydroxide content of the formed hydrated cement paste (Buttler et al., 1983 Hobbs, 1988 Goni et al, 1997). This is due mainly to the reduced permeability of the paste to CO2. However, at higher fly ash contents the resistance to carbonation is significantly reduced (Goni et al, 1997). 

High-volume fly ash concrete is characterized by a high fly ash content and a reduced amount of Portland cement in the mix. The cement/ash replacement ratio is high, and may exceed 50%. Typically, high-volume fly ash concrete mixes contain 100-200 kg/m of cement and 150-300 kg/m of fly ash. 

Portland cements extended with class F fly ash from coal burning power plants may be used for filler applications (Reeves, 1991) and for lightweight cement slurries. The fly ash content may reach up to 50 wt%. 

Power plant coal is usually ground and dried before being fed to a boiler for burning. Moisture content must be reduced to less then 10% for proper handling and burning of coal. This is not an easy task, as coal has a natural tendency to retain water. To avoid pol lution problems, the fly ash content must be low. 

Georgescu, M., Saca, N., 2009. Properties of blended cement with limestone filler and fly ash content. University Politechnica of Bucharest Scientific Bulletin 71 (3). ISSN 1454-2331. Hooton, R.D., Nokke, M., Thomas, M., 2007. Portland-limestone Cement Stage of the Art Report and Gap Analysis for CSA A 3000, SN303. Cement Association of Canada, Toronto. 

The required space velocity depends upon the catalyst configuration and properties (such as activity, stability, expected life), NO, inlet and outlet concentrations, flue gas temperature, flue gas SO3 and SO2 concentrations, fly ash content and composition, and the desired ammonia slip. Space velocities can vary widely depending on these factors. Comparisons based on space velocity should therefore be used with caution. The fly ash concentration and composition dictate the allowable pitch, which in turn establishes the surface area per unit catalyst volume. Figure 10-13 (Robie et al., 1991 A) shows the typical relationship between the NO, reduction efficiency and the flue gas temperature at various space velocities. As the figure shows, higher space velocities (less catalyst volume) at higher temperatures can... 

The use of conventional pozzolanic materials has been studied extensively [29,84,110-112], in particular the use of fly ash. These additives did not prevent a loss in strength and toughness, but they did slow down the rate of loss. Singh and Majumdar [112] reported that the best results, in terms of strength and toughness retention, were obtained with a 40% fly ash content. They pointed out, however, that these high level additions were accompanied by some reduction in the initial properties. The extent of the improvement in durability varied with different fly ashes and natural pozzolans [84,110]. Leonard and Bentur [84] reported that such differences could not be correlated with the pozzolanic activity, but rather with the effect of the fly ash on the interfacial microstructure developed. 

However, adding a small amount of fly ash caused a drastic drop in impact strength and elasticity in MDPE. On a positive side, some increases in modulus and heat deflection temperature were observed in proportion to fly ash contents in melt-conqx)unded samples. 

In terms of processability, the 5% fly ash/PE composites could be rotomolded without much difficulty. At 10% filler contents, however, the molded part qualities deteriorate, evidence fi om presence of air bubbles and difficulties in part removal from the mold. This was especially true in dry-blended sample. The presence of air bubbles suggested lower sinterability of fly ash MDPE compound. The increasing difficulties in sinterability confirm with previous study [3] which showed that shear viscosity increased with fly ash contents. 

The difficulties in part removal suggested that high fly ash contents might have caused PE not to shrink away enough from the mold. In 20% filler contents, part removal was practically impossible without destroying the part itself. 

Po22olans iaclude natural materials such as diatomaceous earths (see Diatomite), opaline cherts, and shales, tuffs, and volcanic ashes or pumicites, and calciaed materials such as some clays and shales. By-products such as fly ashes and siUca fume are also employed. In the United States the proportion of po22olan iaterground with clinker has varied from 15 to over 30%, whereas ia Italy, cements with a 30—40% po22olan content are produced. 

FIG. 17-68 Trends in resistivity of fly ash with variations in fliie-gas temperature and coal sulfur content. °C = (°F — 32) X %. (Ogleshij and Nichols, A Manual of Electrostatic Precipitator Technology, pait 11, Southein Research Institute, Binningham, Ala., Z.970.)... 

In the past, for many air pollution control situations, a change to a less polluting fuel offered the ideal solution to the problem. If a power plant was emitting large quantities of SO2 and fly ash, conversion to natural gas was cheaper than instaUing the necessary control equipment to reduce the pollutant emissions to the permitted values. If the drier at an asphalt plant was emitting 350 mg of particulate matter per standard cubic meter of effluent when fired with heavy oil of 4% ash, it was probable that a switch to either oil of a lower ash content or natural gas would allow the operation to meet an emission standard of 250 mg per standard cubic meter. 

The chlorine content of the fly ash is 4.9 %, the bromine content 0.065 %. A series of brominated aromatic compounds has been adsorbed on this fly ash and treated for 1 h. with air at 300°C. The extraction and analysis yield mixed brominated/chlorinated as well as completely chlorinated products. This is shown for 5 aromatic bromine compounds in Table 2. 

Likewise, fly ash from power plant combustors often contains small amounts of metals or their oxides, which require costly disposal in the ever-shrinking number of approved hazardous waste landfills. Thus, there are economic incentives to recover the metal values as well as to reduce the costs of ultimate disposal. Here, too, the metal content is low, and research is needed to develop economical separation processes. In principle, advances in this area could be translated into recovery of metal values from mine tailings. 

Granulated fly ash [6] can substitute for Portland cement to an extent of 40% to 60%. Fly ash is used in granulated form and has a moisture content around 10% to 20%. The formulation can be used for cementing oil and gas wells within a temperature range of 20° to 250° C. The solution has reduced water absorption and increased sedimentation stability. A formulation [1388] is shown in Table 18-2. Hydrosil (Aerosil) is used to increase the adhesion of the produced cement rock to the casing string. It also reduces the density and water absorption. 

S. A. Abramov, A. P. Krezub, N. A. Mariampolskij, E. S. Bezrukova, and M. A. Egorov. Plugging solution for cementing of oil and gas wells—contains plugging Portland cement and granulated fly ash, of specified moisture content, as active additive. Patent SU 1802089-A, 1993. 

It is assumed that the moisture content of the soil has been determined to be approximately 50% under worst-case conditions. Using this information and the results from vendor tests, it has been determined that a minimum dose of one part solidification reagent to two parts soil is required for the migration control of lead. Testing has shown that the optimum solidification reagent mixture would comprise ca. 50% fly ash and ca. 50% kiln dust. Thus, ca. 7000 t (6364 T) each of fly ash and cement kiln dust would be required. The reagents would be added in situ with a backhoe. As one area of the soil is fixed, the equipment could be moved onto the fixed soil to blend the next section. It may be anticipated that the soil volume would expand by ca. 20% as a result of the fixation process. This additional volume would be used to achieve the required slope for the cap. An RCRA soil/clay cap placed over the solidified material is necessary to prevent infiltration and additional hydraulic stress on the fixed soil. It is estimated that the fixation would reduce lead migration by 40% and that the fixed soil may pass the U.S. EPA levels for lead. 

Furr, A.K., T.F. Parkinson, W.D. Youngs, C.O. Berg, W.H. Gutenmann, I.S. Pakkala, and D.J. Lisk. 1979. Elemental content of aquatic organisms inhabiting a pond contaminated with coal fly ash. N. Y. Fish Game Jour. 26 154-161. 

PCDD/PCDFs are found not only in stack gases but also in solid residues from any combustion process such as bottom ash, slag and fly ash. With advanced technology and better burnout of the ashes and slag (characterized by a low content of organic carbon), PCDD/PCDFs concentrations have declined (Fiedler, 1999). 

To check the influence of PCB oil admixture to the fly ash on the thermodynamic conversion of the whole mixture, the calculations were done for various amounts of organic compounds. The results for power plant ash thermodynamic conversion with temperature rise and with oil-PCB s addition are shown in Fig.l (A and B). These figures show that chlorine appears in the form of HC1 with a characteristic content minimum in the temperature range 1300-1700 K. In the range of 1000 -3000 K the offgas is rich in hydrogen. Maximum value of H2 is determined by the methane decomposition, which occurs above 1200 K. Due to different the... 

Significant dispersion of hexachlorobutadiene has been confirmed by the detection of hexachlorobutadiene at areas which are far removed from release sources (Class and Ballschmiter 1987). A high partition coefficient (log Ko=) value of 3.67 (Montgomery and Welkom 1990) for hexachlorobutadiene indicates that adsorption to soils with high organic carbon content can occur. Wind erosion of contaminated surface soils can then lead to airborne hexachlorobutadiene-containing particulate matter. Levels of hexachlorobutadiene have been detected in fly ash from the incineration of hexachlorobutadiene-containing hazardous waste (Junk... 

From a public health point of view, the concentration of nickel associated with small particles that can be inhaled into the lungs is of greatest concern. The nickel content of aerosols from power plant emissions is not strongly correlated with particle size (Hansen and Fisher 1980). In one modem coal plant, 53% and 32% of nickel in emissions were associated with particles <3 and <1.5 pm in diameter, respectively (Sabbioni et al. 1984). Other studies found that only 17-22% of nickel emissions from coal-fired power plants were associated with particles of >2 pm, and that the mass medium diameter (MMD) of nickel-containing particles from a plant with pollution control devices was 5. 4 pm (Gladney et al. 1978 Lee et al. 1975). In one study, 40% of the nickel in coal fly ash was adsorbed on the surface of the particles rather than being embedded in the aluminosilicate matrix (Hansen and Fisher 1980). Surface-adsorbed nickel would be more available than embedded nickel. 

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