Fly Ash

        Fly Ash is a by-product of a thermal power station, after combustion of coal and production of power. Fly Ash is generated from coal fired generation units. Coal has a dominating role for the power generation in India. Presently there are 70 coal based thermal power plants operating in India. Most of the thermal power plants in India use inferior quality coal, having low calorific value which after combustion, leaves behinds a larger per cent of ash. As the power required in industrial and agricultural sectors increase, production of ash increases. Fly ash contains many toxic elements. Abundant quantities of fly ash are being produced by thermal power plants situated all over the world. At present 100 MT of coal ash is produced annually in India. Fly ash is a complex material and its characterization is quite difficult. It is observed that the overall chemical composition varies from particle to particle and from one sample another. Even initial pulverization of the coal and efficiency of firing have significant influence on the grading of the fly ash produced. It appears that difference in particle size distribution; morphology and surface characteristics of fly ash would influence water demand and reactivity. The principal constituents of fly ash are silica (SiO2), Alumina (Al2O3), Iron oxide (Fe2O3), Calcium oxide (CaO), small amounts of magnesium, sulphur, and unburned carbon. Let us know the properties of the Fly Ash.

  Physical Properties 

           Fly ash particles are typically spherical ranging in diameter from 1 to 150 microns. The type of dust collection equipment used largely determines the range of particle size in any given fly ash. The fly ash from boilers where mechanical collectors are used is coarser than fly ash from electrostatic precipitators. Fly ash consists of the large part of solid or hollow spherical particles of siliceous and aluminous gas with small proportions of thin walled, multifaceted polyhedrousiron content and are irregularly shaped, relatively porous carbon or carbon coated particles. The fineness of fly ash in many a case is to the same extent as that of Portland cement. The color varies from light to dark grey depending upon its carbon contents. The quality of fly ash varies from source to source and is seldom uniform even for the same source because of the important factors like the nature and size of coal, the type of combustion equipment, control of combustion process, mode of fly ash collection etc. the product from a modern power plant when working on base-load is normally quite consistent.

PHYSICAL PROPERTIES OF FLYASH

Chemical Properties 

        In Indian fly ashes, contents of SiO2, Al2O3 are relatively higher than Fe2O3, SO3. The crystalline phases were identified as mullite, magnetite, hematite and quartz. The chemical composition of fly ash and its particle size differ widely for different power plants. This is due to different types of coal used, their various treatment and different types adopted for combustion. Generally, fly ash is differentiated on the basis of degree of fineness and their carbon contents.

CHEMICAL COMPOSITION OF INDIAN FLY ASH 

 Advantages and applications of Fly ash

Fly Ash is having so many advantages due to their unique properties like,

• Strength is more and reduces the permeability.

• Corrosive resistances, specific gravity, lime reactivity.

• Workability: Several reports suggest that fly ash decreases bleeding and segregation, improves plasticity and cohesiveness and permits easier placing and finishing of concrete having no air-entraining agent. Some fly ash reduce the water requirements of test mortars, others (generally of high carbon content) showed increase water requirement above that of control mortars.

• It is cheaply available and fulfills all the requirements.

• Fly Ash can be used for land fillings, soil stabilization.

• Can be used as a partial replacement of cement, as fine aggregate and as coarse aggregates.

• Improves the 20% to 40% of production in agriculture.

• In the manufacturing of Special concretes.

• Finally in the manufacturing of prefabricated components like bricks, blocks, inter locking members, flooring and wall tiles.