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Fly ash?is one of the residues generated in?combustion, and comprises the fine particles that rise with the flue gases. Ash which does not rise is termed?bottom ash. In an industrial context, fly ash usually refers to ash produced during combustion of?coal. Fly ash is generally captured byelectrostatic precipitators?or other particle filtration equipments before the flue gases reach the chimneys of?coal-fired power plants. Since the particles solidify while suspended in the exhaust gases, fly ash particles are generally?spherical?in shape and range in size from 0.5?μmto 100?μm. They consist mostly of?silicon dioxide?(SiO2), which is present in two forms: amorphous, which is rounded and smooth, and crystalline, which is sharp, pointed and hazardous;?aluminium oxide?(Al2O3) and?iron oxide?(Fe2O3). Fly ashes are generally highlyheterogeneous, consisting of a mixture of glassy particles with various identifiable crystalline phases such as?quartz,?mullite, and various?iron oxides.
The ways of fly ash utilization include (approximately in order of decreasing importance):
- Concrete?
- Embankments?
- Grout?and?Flowable fill?production
- Waste stabilization and solidification
- Cement clinkers?production - (as a substitute material for clay)
- Mine reclamation
- Stabilization of?soft soils
- Road subbase?construction
- As?Aggregate?substitute material (e.g. for brick production)
- Mineral filler in?asphaltic concrete
