Fly ash

                       Fly ash Fly ash is a product of combustion of coal. It is normally produced while burning coal in a boiler of a power plant and is generally captured before the flue gas goes to the chimney. The other ash from the boiler is bottom ash which is removed from the bottom of coal fired boiler. Depending upon the type of the coal used, the composition of the fly ash vary widely  but all the types of fly ash include silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO). Fly ash is a fine glass like powder. The particle size of the ash is in microns. The composition of fly ash in case of bituminous coals is as follows: SiO2 – 20%- 60% Al2O3 – 7% – 35% Fe2O3 – 12% – 40% CaO – 2% – 12% LOI – 0%- 12% Fly ash contains environmental toxins in significant amounts. These toxins include arsenic (45 ppm); barium (805 ppm); beryllium (5 ppm); boron (310 ppm); cadmium (3 ppm); chromium (135 ppm); chromium VI (90 ppm); cobalt (35 ppm); copper (110 ppm); fluorine (30 ppm); lead (55 ppm); manganese (250 ppm); nickel (75 ppm); selenium (8 ppm); strontium (775 ppm); thallium (10 ppm); vanadium (250 ppm) and zinc (180 ppm). The use of fly ash as an engineering material is due to its pozzolanic nature, spherical shape, and relative uniformity. The following are the various uses of fly ash: Portland cement and and in materials for grout Embankments and structural fill Waste stabilization and solidification Raw feed for cement clinkers Mine reclamation Stabilization of soft soils Sub base for road Aggregates Flowable fill Mineral filler in asphaltic concrete Roofing tiles Filler in wood and plastic products Fly ash is used as a...