Showing papers on "Fly ash published in 2011"
TL;DR: In this article, the effect of minor additions of limestone powder on the properties of fly ash blended cements was investigated using isothermal calorimetry, thermogravimetry (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques, and pore solution analysis.
849 citations
TL;DR: In this paper, ground fly ash (GFA), with a median particle size of 10.5μm, was used as source material for making geopolymers cured at room temperature, and compressive strength tests and microstructure observations using SEM, EDX, XRD and FTIR were performed.
755 citations
TL;DR: In this article, the effect of both partial and full replacement of natural coarse aggregates by coarse RCA in a fly ash concrete is discussed. And the results obtained showed that while embedding high amount of the RCA could lower the resistance to chloride penetration and carbonation of concrete still comparable design strength to that of the control mix might be achieved.
373 citations
TL;DR: In this article, the interaction between limestone powder and fly ash in ternary composite cement is investigated, and the synergistic effect of fly ash and limestone powder is confirmed and it translates to improved mechanical properties that persist over time.
Abstract: The interaction between limestone powder and fly ash in ternary composite cement is investigated. Limestone powder interacts with the AFm and AFt hydration phases, leading to the formation of carboaluminates at the expense of monosulphate and thereby stabilizing the ettringite. The effect of limestone powder on OPC may be restricted due to the limited amount of aluminate hydrates formed by the hydration of OPC. The additional aluminates brought into the system by fly ash during its pozzolanic reaction amplify the mentioned effect of limestone powder. This synergistic effect between limestone powder and fly ash in ternary cements is confirmed in this study and it translates to improved mechanical properties that persist over time.
345 citations
TL;DR: In this article, a comprehensive study on the durability properties of concrete containing polypropylene fiber and fly ash was performed, and the results showed that the positive interactions between polypropane fibers and fly-ash lead to the lowest drying shrinkage of fibrous concrete with fly ash.
319 citations
TL;DR: In this article, the authors studied the geopolymerisation of mechanically activated fly ash at ambient (27 degrees C) and elevated (60 degrees C), by isothermal conduction calorimeter.
300 citations
TL;DR: In this article, the adsorption behavior of some low-cost adsorbents such as peanut husk charcoal, fly ash, and natural zeolite, with respect to Cu 2+, and Zn 2+ ions, has been studied in order to consider its application to the purification of metal finishing wastewater.
298 citations
TL;DR: In this article, the properties of fly-ash-based geopolymer concrete (GPC) were studied using regression analysis to identify tendencies and correlations within the mechanical properties of GPC.
Abstract: The mechanical properties of fly-ash-based geopolymer concrete (GPC) were studied. Experimentally measured values of the static elastic modulus, Poisson’s ratio, compressive strength, and flexural strength of GPC specimens made from 25 fly ash (FA) stockpiles from different sources were recorded and analyzed. The results were studied using regression analysis to identify tendencies and correlations within the mechanical properties of GPC. It was found that the mechanical behavior of GPC is similar to that of ordinary portland cement (OPC) concrete, suggesting that equations, akin to those given by ACI 318-08, could be applied for GPC to determine its flexural strength and static elastic modulus. The validity of an equation to determine the density of GPC as a function of FA fineness was also put forward.
287 citations
TL;DR: In this paper, an analysis of fly ash paste morphology was performed using scanning electron microscopy (SEM/EDS) and microstructural properties with X-ray Diffraction (XRD) analysis.
Abstract: Fly ashes (FA) are byproducts of electricity production from mineral coal in thermoelectric power plants. The pozzolanic properties of FA have been utilized in various applications, including structural concrete, yet the large part of FA is still discarded into the environment. To promote greater FA usage, this study aims to produce a dense matrix, with mechanical properties satisfactory for civil engineering projects, from alkali-activated fly ash-based geopolymers. Three variables were studied: the Na2O/SiO2 molar ratio (N/S 0.20, N/S 0.30 and N/S 0.40); curing temperature in the first 24 h (50, 65 and 80 °C); and age (1, 7, 28, 91 and 180 days). For this study, alkali-activated fly ash pastes and mortars were prepared. In pastes, morphology was studied using scanning electron microscopy (SEM/EDS) and microstructural properties with X-ray Diffraction (XRD) analysis. Mortars were evaluated according to their mechanical performance measured using compression strength tests. Compression strength results were analysed using ANOVA. The results show that the N/S molar ratio plays an important role in the mechanical and morphological characteristics of geopolymers. The mortars prepared with a N/S 0.40 molar ratio had the greatest compression strength. The analysis of paste morphology revealed that N/S 0.40 pastes had a denser appearance, which is in agreement with results of compression strength tests.
274 citations
TL;DR: Fly ash and steel slag could be effective in mitigating heavy metal accumulation in rice grown on multi-metal contaminated acidic soils.
264 citations
TL;DR: It was found that the synthesized geopolymer has higher removal capacity for lead ions when compared with that of raw coal fly ash and that Langmuir isotherm model is the best fit for the experimental data than Freundlich model.
TL;DR: In this article, the effect of fineness of fly ash on the setting time of geopolymer paste, workability, strength development, and drying shrinkage of the mortars made from classified fine high-calcium fly ash was investigated.
Abstract: In this paper, the synthesis of high-strength geopolymer using fine high-calcium fly ash was studied. The effect of fineness of fly ash on the setting time of geopolymer paste, workability, strength development, and drying shrinkage of geopolymer mortars made from classified fine high-calcium fly ash was investigated. Air-classified fly ash with three different finenesses—coarse original fly ash (CFA), medium-fineness fly ash (MFA), and fine fly ash (FFA)—from the Mae Moh Power Station was used for this study. The heat-cured geopolymers were activated with sodium hydroxide (NaOH) and sodium silicate. A small amount of water was incorporated for workability. The results indicate that the setting time of paste decreases with an increase in fly-ash fineness. The flow, strength, and drying-shrinkage characteristics of mortars were improved using fine fly ash. Geopolymer mortars with high 28-day compressive strength of 86.0 MPa were obtained.
TL;DR: In this article, the properties of self-compactability parameters (slump flow, J-ring, V-funnel, L-box and U-box), strength properties (compressive and splitting tensile strength), and durability properties (deicing salt surface scaling, carbonation and rapid chloride penetration resistance).
TL;DR: The effectiveness of fly ash use in the stabilization of organic soils and the factors that are likely to affect the degree of stabilization were studied in this paper, where unconfined compression and resilient modulus tests were conducted on organic soil.
Abstract: The effectiveness of fly ash use in the stabilization of organic soils and the factors that are likely to affect the degree of stabilization were studied. Unconfined compression and resilient modulus tests were conducted on organic soil–fly ash mixtures and untreated soil specimens. The unconfined compressive strength of organic soils can be increased using fly ash, but the amount of increase depends on the type of soil and characteristics of the fly ash. Resilient moduli of the slightly organic and organic soils can also be significantly improved. The increases in strength and stiffness are attributed primarily to cementing caused by pozzolanic reactions, although the reduction in water content resulting from the addition of dry fly ash solid also contributes to strength gain. The pozzolonic effect appears to diminish as the water content decreases. The significant characteristics of fly ash that affect the increase in unconfined compressive strength and resilient modulus include CaO content and CaO/SiO2...
TL;DR: In this paper, the authors investigated the effect of fly ash as a supplement to concrete and found that the fly ash concrete samples showed less drying shrinkage than control concrete samples when designed for the same 28-day compressive strength of the control concrete.
TL;DR: In this paper, a comparative study of the residual compressive strength at different temperatures of AAFA pastes chemically activated using sodium silicate with three different concentrations named 20, 30 and 40 (wt%).
TL;DR: Based on the results from the experimental investigations, it is believed that the recycled aggregate concrete can be successfully applied to structural concrete members.
TL;DR: Comparison of fly ash-based geopolymer systems with classical Portland cement stabilization methods has also been accomplished, showing that the leachate pH was the most important variable for the immobilization of metals.
15 Apr 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors report on the characterisation of fly ash from three Australian power stations in terms of elemental composition, phase composition, particle size, density and morphology, and the effect of the source fly ash characteristics on the hardened product is discussed, as well as implications for high temperature applications.
Abstract: Fly ash characteristics cannot be assumed to be constant between power stations as they are highly dependent on the coal source and burning conditions. It is critical to understand the characteristics of fly ash in order to produce geopolymers suitable for high temperature applications. We report on the characterisation of fly ash from three Australian power stations in terms of elemental composition, phase composition, particle size, density and morphology. Geopolymers were synthesised from each of the fly ashes using sodium silicate and sodium aluminate solutions to achieve a range of Si:Al compositional ratios. Mechanical properties of geopolymer binders are presented and the effect of the source fly ash characteristics on the hardened product is discussed, as well as implications for high temperature applications. It was found that the twenty eight day strength of geopolymers is largely dependent on the sub 20 μm size fraction of the fly ash. Strength loss after high temperature exposure was found to be dependent on the concentration of iron in the fly ash precursor and the Si:Al ratio of the geopolymer mixture.
TL;DR: In this paper, a feasibility study is performed on geopolymerization of mine tailings so that they can be recycled and utilized as construction material, and the results show that the Si/Al ratio and the alkalinity have profound effects on the mechanical and micro-structural properties of the mine-tailings-based geopolymers.
TL;DR: In this paper, the authors investigated the role of Bacillus megaterium ATCC 14581 on compressive strength, water absorption and water impermeability of fly ash-amended mortar and concrete.
TL;DR: 15% Mn/γ-Fe(2)O(3)-250 may be a promising sorbent for elemental mercury capture in the presence of a high concentration of SO(2).
TL;DR: In this paper, a review on the concentration of As in FA, its fate and behaviour as hazardous element on human health, environment quality and on mitigation strategies to accomplish environmental management is presented.
Abstract: Fly ash (FA) generated as a waste produced from thermal power plants globally has started gaining as a potentially significant anthropogenic source of arsenic (As). In India electricity generation is predominantly dependent upon coal-based thermal power plants and are being producing huge amount of FA. Coal contains many toxic metals, arsenic is one of those, which is significantly toxic for aquatic and terrestrial life including human being. Coal used in Indian thermal power plants is mainly bituminous and sub-bituminous and which on combustion generate over 40% of FA. Generated FA is being disposed to open ash pond in thin slurry form. More than 65,000 acre of land in India is occupied for storage of this massively generated quantity of FA. Dumping of FA in open ash pond causes serious adverse environmental impacts owing to its elevated trace element contents, in particular the As which causes ecological problems. Although, the As problem in our country is not new, in recent years the occurrence of As contamination cases of agricultural soil, ground water as well as human health has resulted a great concern for its mitigation. Very recently India has been charged for being a “dumping hub for As”. Utilization of FA in India is still infancy (more than 38%) as compared to developed countries (more than 70%). In India FA is used particularly in cement production, brick industry, as road base, as amendments in the restoration ecology and forestry. This review emphasized on the concentration of As in FA, its fate and behaviour as hazardous element on human health, environment quality and on mitigation strategies to accomplish environmental management.
TL;DR: In this article, the role of fly ash and biomass ash on the strength development of low-swelling Bangkok clay is investigated via unconfined compressive (UC) test and thermal gravity (TG) analysis.
TL;DR: In this paper, the possibility of making construction bricks by using the hematite tailings from western Hubei province of China was investigated, where the additives of clay and fly ash were added to the raw materials to improve the brick quality.
TL;DR: The model developed from literature data could be easily extended to the experimental data, with bottom ash as partial replacement of sand with some modifications, and the importance of different input parameters is also given for predicting the strengths at various ages using neural network.
TL;DR: The Siberian Trap flood basalts resulted in the heating and combustion of coals and organic-rich sediments at the time of the Permian mass extinction, and the presence of char in distant lake sediments linked to the eruption suggests that fly ash could have been generated by the coal combustion, and then dispersed globally, creating toxic marine conditions as discussed by the authors.
Abstract: The eruption of the Siberian Trap flood basalts resulted in the heating and combustion of coals and organic-rich sediments at the time of the Permian mass extinction. The presence of char in distant lake sediments linked to the eruption suggests that fly ash could have been generated by the coal combustion, and then dispersed globally, creating toxic marine conditions.
TL;DR: In this paper, the effect of chemical admixtures on the properties of fly ash geopolymer was studied to overcome the rapid set of the geopolymers in the presence of high viscosity of sodium silicate solution.
Abstract: Owing to the high viscosity of sodium silicate solution, fly ash geopolymer has the problems of low workability and rapid setting time. Therefore, the effect of chemical admixtures on the properties of fly ash geopolymer was studied to overcome the rapid set of the geopolymer in this paper. High-calcium fly ash and alkaline solution were used as starting materials to synthesize the geopolymer. Calcium chloride, calcium sulfate, sodium sulfate, and sucrose at dosages of 1wt% and 2wt% of fly ash were selected as admixtures based on concrete knowledge to improve the properties of the geopolymer. The setting time, compressive strength, and degree of reaction were recorded, and the microstructure was examined. The results show that calcium chloride significantly shortens both the initial and final setting times of the geopolymer paste. In addition, sucrose also delays the final setting time significantly. The degrees of reaction of fly ash in the geopolymer paste with the admixtures are all higher than those of the control paste. This contributes to the obvious increases in compressive strength.
TL;DR: In this paper, the potential benefits of the synergistic effect of an ASTM C 618 Class F fly ash (FA) and a high-range polycarboxylate superplasticizer (SP) in the production of conventional concrete are discussed.
Abstract: This article presents experimental research work oriented toward developing practical design tools for industrial application, and illustrates the potential benefits of the synergistic effect of an ASTM C 618 Class F fly ash (FA) and a high-range polycarboxylate superplasticizer (SP) in the production of conventional concrete. The different concretes considered in this study were produced with mass substitutions of cement by FA between 15% and 75%, and a target slump of 200 mm ± 20 mm. The total water content was minimized through the use of an optimum SP dosage that resulted in water reductions of 18%, 15% and 11% respectively for the reference mixtures of w/b = 0.5, w/b = 0.55, and w/b = 0.6, which leads to the same percentage reductions of cement. Heat release and heat flow were analyzed through isothermal and semi-adiabatic calorimetry, illustrating that heat release per unit mass of cement is independent of w/b, contrasting with the time of setting results that vary by several hours between the three different w/b ratios. The paper highlights the beneficial effect of the SP in terms of cement reduction and slump retention. Correlations between the FA substitution and slump loss, setting times, compressive strength and static modulus of elasticity (E) were established and they represent very useful tools for the practical applications of the results. Compressive strength developments up to an age of 56 d are also reported, as well as correlations between the modulus of rupture and compressive strength or splitting tensile strength at an age of 28 d.
TL;DR: In this paper, low calcium ground fly ash and metakaolin were activated with a sodium-silicate solution and cured under ambient and heat conditions, and the resulting mature aluminosilicate composites were indented by several series of grids consisting of approximately 100 indents in each.
Abstract: Low calcium ground fly ash and metakaolin were activated with a sodium-silicate solution and cured under ambient and heat conditions. The resulting mature aluminosilicate composites were indented by several series of grids consisting of approximately 100 indents in each. The effective material volume affected by an indent was ≈1 μm3. Statistical histogram plots of elastic properties of the main reaction product (N-A-S-H gel) as well as of other material phases were constructed. The deconvolution of histograms via four Gaussian distributions testified that the mature N-A-S-H gel has almost the constant intrinsic Young’s modulus ≈17–18 GPa, irrespective of the curing procedure and activated material, i.e. fly ash or metakaolin.