Increase In Fly Ash Content Research Articles

Compaction characteristics and corrosivity of Indiana class-F fly and bottom ash mixtures

Fly ash and bottom ash are the residual by-products of coal burning to produce electricity. They are typically treated as a waste, disposed together in ponds. Reutilization of these waste materials in civil engineering applications that require large volumes of fill or back-fill materials, such as embankments and retaining structures, is beneficial. The literature contains only limited information on the use of mixtures of fly and bottom ash in these types of applications. One advantage of using ash mixtures in the proportions in which they exist in the disposal ponds is that there are no costs associated with mixing the ashes in situ at the time of construction. In addition, use of ash preserves traditional materials and allows savings on both land acquisition and disposal operations. This study presents a laboratory investigation on the compaction characteristics and corrosivity of class-F fly and bottom ash mixtures. Standard compaction, maximum and minimum density, electrical resistivity, and pH tests were conducted on ash mixtures with different mixture ratios: 50%, 75%, and 100% fly ash content by weight. The compaction test results showed that, with increasing fly ash content, the maximum compacted dry densities decreased and the corresponding water contents increased. Comparisons with the maximum density test results revealed that relative compaction is a more appropriate quantity to control the density of ash mixtures than relative density. The electrical resistivity values of the ash mixtures also varied with fly ash content, and were found to be mainly a function of water content. Two corrosivity indicators (electrical resistivity and pH) suggested that ash mixtures may be potentially corrosive. The results presented in this paper show that ash mixtures have properties that allow their use in place of traditional materials in the construction of fills or backfills.

DRY SLIDING WEAR BEHAVIOUR OF FLYASH REINFORCED ZA-27 ALLOY BASED METAL MATRIX COMPOSITES

In the present investigation, an attempt has been made to evaluate the wear rate of ZA-27 alloy composites reinforced with fly ash particles from 1 to 3 wt% in steps of 1 wt%. The compo-casting method has been used to fabricate the composites using Raichur fly ash of average size 3-5 microns. The wear specimens are tested under dry conditions using a pin-on-disc sliding wear testing machine with wear loads of 20-120 N in steps of 20 N, and the sliding distances in the range of 0.5 km to 2.5 km. The results indicate that the wear rate of the composites is less than that of the matrix alloy and it further decreases with the increase in fly ash content. However, the material loss in terms of wear rate and wear volume increases with the increase in load and sliding distance, both in the cases of composites and the matrix alloy. An increase in the applied load increases the wear severity by changing the wear mechanism from abrasion to particle-cracking induced delamination wear. It is found that with the increase in fly ash content, the wear resistance increases monotonically. The observations have been explained using scanning electron microscope (SEM) analysis of the worn surfaces of the composites.

Application of phosphogypsum in soil stabilization

This paper describes the application of phosphogypsum with cement and fly ash for soil stabilization. Atterberg limits, standard Proctor compaction and unconfined compressive strength tests were carried out on cement, fly ash and phosphogypsum stabilized soil samples. Treatment with cement, fly ash and phosphogypsum generally reduces the plasticity index. The maximum dry unit weights increase as cement and phosphogypsum contents increase, but decrease as fly ash content increases. Generally optimum moisture contents of the stabilized soil samples decrease with addition of cement, fly ash and phosphogypsum. Unconfined compressive strengths of untreated soils were in all cases lower than that for treated soils. The cement content has a significantly higher influence than the fly ash content. The use of two waste by-products, phosphogypsum and fly ash may provide an inexpensive and advantageous construction product.

Flexural responses of hybrid steel–polyethylene fiber reinforced cement composites containing high volume fly ash

Strain hardening and multiple cracking behavior of hybrid fiber reinforced cement composites containing different hybrid combinations of steel and polyethylene (PE) fibers under four-point bending are reported. The total volume fraction of fibers was kept constant at 2.5% to maintain a workable mix. Effects of increase in fly ash content as partial replacement of cement beyond 50%, such as 60% and 70% on the flexural response of hybrid steel–PVA (polyvinyl alcohol) and steel–PE fiber composites are also evaluated here. Among composites with different volume ratios of steel and PE fibers, the composite with 1.0% steel and 1.5% PE was found to show the highest flexural strength and that with 0.5% steel and 2.0% PE exhibited highest deflection and highest flexural toughness. Generally, the steel–PE hybrid composites exhibited lower flexural strength but higher deflection capacity than steel–PVA hybrid composites. The rate of strength loss after peak load in steel–PE hybrid composites was found low compared to steel–PVA hybrid system. The 50% replacement of cement by fly ash is found to be an optimum fly ash content in hybrid fiber composites.

Microstructure, mechanical properties, wear and corrosion behaviour of Al–Si/FLYASHP composite

Aluminium based metal matrix composite containing 5, 10, and 15% by weight of flyash particulates was successfully synthesised using a stir cast method. The microstructure of these stir cast composites exhibited relatively uniform distribution of flyash particles. Mechanical properties such as density, hardness, and tensile strength were investigated. Sliding wear behaviour, slurry erosive wear behaviour, and fog corrosion behaviour of the composite were also investigated in the heat treated condition. The results of wear studies have shown that the resistance to wear increases with increasing percentage of flyash particulates. The addition of flyash particles showed appreciable change in overall density values. The bulk hardness and tensile strength increased with increasing flyash content. The presence of flyash particles appeared to initiate pitting corrosion.

Synthesis-microstructure-mechanical properties-wear and corrosion behavior of an Al-Si (12%)—Flyash metal matrix composite

In the present investigation, Aluminium based metal matrix composite containing up to 15% weight percentage of flyash particulates were successfully synthesized using vortex method. The properties like density, hardness, microhardness, ductility and ultimate tensile strength were investigated. The MMC produced was also subjected to corrosion, dry sliding wear and slurry erosive wear test to investigate its behavior under different material wearing conditions. The results of microhardness revealed higher hardness of the matrix material in the immediate vicinity of flyash particle. The addition of flyash particles reduces the density of composite while increasing some of their mechanical properties. The results of wear studies have shown that the resistance to wear increases with increase in percentage of flyash. Corrosion resistance decreases with increase in flyash content. The macrostructural and microstructural characteristics of the MMC were investigated with particular emphasis on the distribution of flyash particles in the matrix. Macrostructural studies have shown near uniform distribution of flyash particles in matrix. Analysis of fractured surface of tensile test specimen is also made which revealed brittle fracture behavior of MMCs.

Effect of fly ash particles on the mechanical properties of aluminium casting alloy A535

Fly ash is a lightweight coal combustion byproduct (CCB) which is separated from the exhaust gases of power generating plants using suspension fired furnaces in which pulverised coal is used as the fuel. Its physical and chemical properties make it a useful construction and industrial material, especially in cement manufacturing, concrete, liquid waste stabilisation, and hydraulic mine backfill. The addition of fly ash into aluminium alloys has the potential to reduce the cost and density of aluminium castings while improving other physical and mechanical properties of the resulting metal matrix composites (MMCs). In the present study, the effect of fly ash addition on the mechanical properties of aluminium casting alloy 535 (A535) was investigated by means of hardness measurements, tensile testing, Charpy impact testing, optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and X-ray fluorescence spectroscopy (XFS). The unreinforced A535 and its MMCs containing a mixture of 5 wt-% fly ash and 5 wt-% silicon carbide, 10 wt-% fly ash and 15 wt-% fly ash were investigated in the as cast and heat treated conditions. The results show that increasing the fly ash content of the melt increased the porosity of the castings, which ultimately affected the tensile and impact properties of the MMCs. The microhardness, tensile strength and Charpy impact energy of the composites decreased with increasing fly ash content. The loss in mechanical properties and impact resistance of the MMCs is attributed partly to the depletion of solid solution strengthening magnesium atoms from the matrix and partly to porosity.

Effect of Fly Ash on Engineering Properties of Expansive Soils

This note presents a study of the efficacy of fly ash as an additive in improving the engineering characteristics of expansive soils. An experimental program has evaluated the effect of the fly ash content on the free swell index, swell potential, swelling pressure, plasticity, compaction, strength, and hydraulic conductivity characteristics of expansive soil. The plasticity, hydraulic conductivity and swelling properties of the blends decreased and the dry unit weight and strength increased with an increase in fly ash content. The resistance to penetration of the blends increased significantly with an increase in fly ash content for a given water content. Excellent correlation was obtained between the measured and predicted undrained shear strengths.

Structural Properties and Reactivities of Ca(OH)2/Fly Ash Sorbents for Flue Gas Desulfurization

Ca(OH)2/fly ash sorbents were characterized and tested for reactivity toward SO2 at conditions similar to those in the bag filters in the dry and semidry flue gas desulfurization processes. The sorbents were mesoporous, and their specific surface areas linearly correlated with their specific total pore (1.7−300 nm) or mesopore (2−50 nm) volumes. The 1 h utilization of Ca in a sorbent increased, in general, with increasing fly ash content. Sorbents with Ca(OH)2 contents larger than 33 wt % had higher weights of SO2 captured per unit weight of sorbent than Ca(OH)2 had alone, and the sorbent with 70 wt % Ca(OH)2 had the maximum capture. The 1 h utilizations of Ca for the sorbents and Ca(OH)2 increased almost linearly with increasing specific surface area or pore volumes of the sorbent. The SO2 captured per unit surface area or pore volume of the sorbent decreased almost linearly with smaller Ca(OH)2 content. The reactivities of the sorbents were enhanced mainly by their large specific surface areas and to a ...

Effects of fly ash additions on the mechanical and other properties of porcelainised stoneware tiles

The effect of fly ash additions on the mechanical properties of porcelainised stoneware tile composition has been investigated. Fly ash additions in the range of 0–40 wt% have been added in to the tile body composition, wet milled, spray dried, shaped and fired at 1250°C. The MOR strength improved with increasing fly ash content and reached maximum when 25–30 wt% fly ash used, and with greater additions it decreased. A linear correlation between strength development and mullite formation was found. The tiles with 25 wt% fly ash had improved bending strength, abrasion resistance and hardness compared to the conventional tiles and conform to all other properties at an EN standard specification.

A New Organophosphorus Insecticides Removal Process Using Fly ASH

Fly ash and soil mixtures with a range of fly ash content from 1 to 100% were used to study adsorption and desorption of four organophosphorus insecticides, ethyl parathion, methyl parathion, fenitrothion and fenthion, in batch experiments. The object of the study was to develop a treatment process using fly ash as sorbent material to isolate/immobilize organic contaminants from aqueous solutions. The adsorption isotherms fit the Freundlich equation x/m=KdC1/n. The Kd values increase with the increase of the fly ash content. The isotherms seem to fit the S type, in mixtures of soil with a fly ash content from 0 to 10%, which implies that adsorption becomes easier as the concentration in the liquid phase increases. In mixtures of soil with a fly ash content from 25 to 50% the isotherms become L type and correspond to a decrease of site availability as the solution concentration increases. Finally in mixtures of soil with a fly ash content over 50%, C type adsorption was observed which correspond to a constant partition of the insecticides between the bulk solution and the adsorbent. Mass balance estimations show that the mean percent amounts of insecticides for a range of concentration 0.5–15 mg/l, removed by adsorption in the soil sample are 81.56 % for ethyl parathion, 48.97 % for methyl parathion, 67.06 % for fenitrothion and 86.65 % for fenthion. The adsorption increases as the fly ash content increased and reach the 100% in the “pure” fly ash. The adsorbed amounts of insecticides in mixtures of soils with >50% fly ash content, are up to 99%. In contrast, the amounts of desorption in water decrease as the fly ash content increase. The results of this research demonstrate that the fly ash shows a significant capacity for adsorption of organophosphorus compounds from aqueous solution and can be used for pesticide removal process.

Adsorption-desorption studies of selected herbicides in soil-Fly ash mixtures.

Fly ash and soil mixtures with a range of fly ash content from 0 to 100% were used to study the adsorption and desorption of herbicides atrazine, propazine, prometryne, propanil, and molinate in batch experiments. The isotherms shapes according to Giles classification (Giles et al., 1960) were S, L, and H as the substrate changed from sandy clay loam (SCL) to fly ash, depending on the percent of fly ash in the mixture. The adsorption isotherms fit the Freundlich equation x/m = K(f) C(1/)(n)(). The K(f) values increase with the increase of the fly ash content. The mean percent amounts of herbicides, for a range of concentration 1-20 mg L(-)(1), adsorbed on the soil were 21.9% for atrazine, 50.7% for propazine, 29.04% for prometryne, 43.14% for molinate, 31.35% for propachlor, and 46.34% for propanil. Mass balance estimations show that the adsorbed amounts of the herbicides increase along with the fly ash content in the sorbent mixture and reach the 99% in the "pure" fly ash. In contrast, the amounts desorbed with water decrease as the fly ash content increases. The n values ranged from 0.82 to 3.05 indicating that the carbon content of fly ash plays a significant role during the sorption process and an increase of heterogenity of solid substrate. The increase of the amounts desorbed with acetone indicates that the sorption of organic compounds onto fly ash is believed to occur principally via the weak induction forces of London or dispersion forces which are characteristic of the physical adsorption process. The results of this research demonstrate that the fly ash shows a significant capacity for adsorption of organic compounds from aqueous solution.

Influence of composition and curing on drying shrinkage of aerated concrete

The process of drying of many materials is accompanied by dimensional changes, which induce cracks in the structure. This phenomenon is particularly significant in acrated concrete owing to its high total porosity and specific surface of pores. The factors influencing drying shrinkage of aerated concrete are widely different from that of normal concrete because of the presence of coarse aggregates in the latter. This paper discusses the results of statistically designed experiments conducted to ascertain the influence of composition on the drying shrinkage of non-autoclaved and autoclaved aerated concrete. Detailed single factor experiments were conducted to assess the influence of basic constituents of the mix on drying shrinkage whereas fractional factorial experiments were used for the interaction effects and the influence of some additives. It was observed that increase in lime-cement ratio and fly ash content increases drying shrinkage. Significant shrinkage reduction is obtained by autoclaving, suggesting that drying shrinkage is predominantly a function of the physical structure of the hydration product.

Studies on Hydration in High-Volume Fly Ash Concrete Binders

Pastes made with different fly ash contents, water-cementitious ratios (w/cm), and admixtures were tested for up to 90 days. Strength development, thermal analysis, silicate polymerization analysis, pore structure analysis, x-ray diffraction analysis, and scanning electron microscopy were employed to study the hydration progress, hydration product, and microstructure of the pastes. It is determined that admixtures affect the progress of hydration, and activator admixtures can accelerate the hydration of high-volume fly ash (HVFA) concrete binders. The total porosity increases with increasing fly ash content and w/cm and decreases with increasing age. The presence of fly ash can improve the pore size distribution. The fly ash in HVFA systems cannot be fully hydrated. The changes of (SiO4) sup (4-) polymerization degree behave irregularly during the hydration of HVFA systems. The contents of monomer and dimer in fly ash are very low, and the activity of fly ash is low. It is suggested that the fly ash content in HVFA concrete should be lower than 70%.

Chloride thresholds in marine concrete

This paper reports results from an ongoing study of the performance of fly ash concrete in marine exposure. Reinforced concrete specimens exposed to tidal conditions were retrieved at ages ranging from 1 to 4 years. Steel reinforcement mass losses are compared with chloride contents at the location of the bar for concrete specimens of various strength grades and with a range of fly ash levels. The maximum level of chloride that could be tolerated without significant mass loss due to corrosion was found to vary with fly ash content. This threshold chloride level decreased with increasing fly ash content; values obtained were 0.70%, 0.65%, 0.50% and 0.20% acid-soluble chloride (by mass of cementitious material) for concrete with 0%, 15%, 30% and 50% ash, respectively. Despite the lower threshold values, fly ash concrete was found to provide better protection to the steel under these conditions, due to its increased resistance to chloride ion penetration.

Creep, shrinkage, frost, and sulphate resistance of high strength concrete

A comprehensive study was undertaken to determine the shrinkage, creep, and durability of high strength concrete (50–70 MPa) containing silica fume and lignite fly ash. The concrete mixtures contained normal CSA type 10 (ASTM type 1) portland cement, 10% condensed silica fume, and different amounts of fly ash that varied between 0 and 80% of the weight of binder in the mixture. The aggregates-to-binder ratio by weight was maintained at 5 and the weight of the superplasticizer was varied between 1.5% and 2.2% of the binder while the water-to-binder ratio was maintained at 0.27. The test program consisted of compressive strength tests at various ages on concrete cylinders; drying shrinkage tests at room temperature; creep tests of sealed and unsealed concrete at room temperature (21 °C (70°F)) and at high temperatures (up to 232 °C (450°F)) under three different stress regimes; frost resistance tests on concrete prisms up to 300 freezing and thawing cycles; and sulphate resistance tests on concrete prisms immersed in 5% Na2SO4 solution for up to 10 months. The results indicated that up to 60% fly ash replacement with 10% silica fume showed either superior or similar 28- and 56-day compressive strengths when compared with the 100% cement control mixture. Fly ash + silica fume concrete indicated lower shrinkage and long-term creep. Creep increased with increase in temperature due to physico-chemical processes, which were confirmed by microstructure analysis using the scanning electron microscope. The creep and shrinkage data of high fly ash + silica fume concrete fitted well to the current ACI creep and shrinkage model. Replacement of cement by up to 35% fly ash and 10% silica fume indicated enhanced frost resistance, without any air-entrainment. The addition of 8% air-entrainment to the 20% fly ash + 10% silica fume mixture increased the durability factor by about 10%. For the 50% fly ash + 10% silica fume mixture, the frost durability factor was found comparable to that of the 100% cement control mixture, and air entrainment did not improve its value appreciably. Sulphate resistance of concrete made with 100% CSA type 10 cement was found satisfactory; however, with increasing fly ash contents (up to 50%), the expansion due to sulphate action was suppressed. A study of matrix morphology and microstructure bonding, using the scanning electron microscope, helped to explain the observed results in a comprehensive manner. Key words: creep, shrinkage, compressive strength, frost resistance, durability factor, sulphate resistance, fly ash, silica fume, high-strength concrete, SEM micrograph, matrix morphology.