As-received Fly Ash Research Articles

Glass matrix composites from coal flyash and waste glass

Glass matrix composites have been fabricated from waste materials by means of powder technology. Flyash from coal power stations and waste glass, residue of float glass production, were used. Commercial alumina platelets were employed as the reinforcing component. For flyash contents up to 20% by weight nearly fully dense compacts could be fabricated by using relatively low sintering temperatures (650°C). For higher flyash contents the densification was hindered due to the presence of crystalline particles in the as-received flyash, which jeopardized the viscous flow densification mechanism. The addition of alumina platelets resulted in better mechanical properties of the composites than those of the unreinforced matrix, despite a residual porosity present. Young's modulus, modulus of rupture, hardness and fracture toughness increase with platelet volume fraction. The low brittleness index of the composites ( B ≈ 3 μm −1 2 ) suggests that the materials have good machinability. A qualitative analysis of the wear behaviour showed that the composite containing 20% by volume platelet addition has a higher wear resistance than the unreinforced matrix. Overall, the results indicate that the materials may compete with conventional glasses and glass-ceramics in technical applications.

Synthesizing mullite from beneficiated fly ash

In the United States, approximately 50 million tonnes of fly ash are generated by electrical utilities annually. The current consumption rate for fly ash materials is less than 20% because most fly ash materials do not meet market specifications and the quality of the ash is inconsistent. A beneficiation process that produces quality-controlled fly ash components has been developed. The synthesis of mullite as a refractory material is one industrial application for the silicate sphere component from the beneficiated fly ash. As-received (untreated) fly ash did not produce a usable mullite refractory. This article discusses the fly ash beneficiation process and mullite synthesis.

Acidolysis of coal fly ash by Aspergillus niger

The kinetics of aluminium extraction were investigated, using as-received and calcined fly ash samples and a pure culture of Aspergillus niger. This fungus metabolized sucrose to citric and oxalic acids, which were involved in the acidolysis of fly ash. Aluminium extraction from as-received fly ash was only 5–8%, whereas from calcined fly ash it was up to 93.5%. The order of reaction and the overall reaction rate constant were determined by the van't Hoff technique with respect to the concentration of calcined fly ash. A linearized form of a modified Monod expression was applied to the experimental data to assess the kinetic constants for the acidolysis process. Statistically designed experiments were carried out with calcined fly ash and synthetic solutions containing citric and oxalic acids to determine the optimum leaching conditions. The acidolysis reaction mechanism is discussed.

Concrete Incorporating High Volumes of ASTM Class F Fly Ash

Abstract This paper gives results of an investigation undertaken to develop additional data on mechanical properties, and freezing and thawing resistance of high-volume Class F fly ash concrete made with ASTM Types I and III cements. A series of eight concrete mixtures involving twelve batches, each 0.06 m3 in volume, were made at a water-to-cementitious materials ratio of 0.32 ± 0.01. The fly ash-to-(fly ash + cement) ratio was 0.56. The cement content of the mixtures was 154 kg/m3. All mixtures were air-entrained and superplasticized. The mixtures incorporated Type I and Type III cements, various combinations of as-received fly ash, beneficiated fly ash, and condensed silica fume. From the test results, it is concluded that high-volume fly ash concrete has excellent mechanical properties and satisfactory resistance to repeated cycles of freezing and thawing. The use of ASTM Type III cement appears to be essential when high strengths at early ages are required. For concretes made with ASTM Type I cement, the use of beneficiated fly ash, and beneficiated fly ash and condensed silica fume, does little to enhance the properties of concrete compared with “as received” fly ash. For concrete made with ASTM Type III cement, the benefits of using beneficiated Class F fly ash and condensed silica fume are not clear.