FLY ASH UTILIZATION

•All the coal based power stations put together generate more than 100 million tonnes of fly-ash per annum.

•The Fly Ash Mission of TIFAC has made several useful recommendations for utilization of fly-ash in the manufacture of cement, bricks, pavement materials, floor tiles, wall panels etc.

• In agriculture, road construction, land-filling and back-filling of mines

• Armed with the findings of the national laboratories that fly ash is superior in strength and durability as compared to conventional products,

• The Ministry of Power is taking steps to make the use of flyash products mandatory in road and bridge construction, and construction of Government buildings as is being done in the developed countries and to provide fiscal incentives initially to supplement the market mechanism for taking up production and promotion of fly ash products.

• Fly ash is one of the residues generated in the combustion of coal. Fly ash is generally captured from the chimneys of coal-fired power plants, and is one of two types of ash that jointly are known as coal ash; the other, bottom ash, is removed from the bottom of coal furnaces.

• Depending upon the source and makeup of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO), both being endemic ingredients in many coal bearing rock strata.

Class F fly ash• The burning of harder, older anthracite and

bituminous coal typically produces Class F fly ash. This fly ash is pozzolanic in nature, and contains less than 10% lime (CaO).

• Possessing pozzolanic properties, the glassy silica and alumina of Class F fly ash requires a cementing agent, such as Portland cement, quicklime, or hydrated lime, with the presence of water in order to react and produce cementitious compounds.

• Alternatively, the addition of a chemical activator such as sodium silicate (water glass) to a Class F ash can leads to the formation of age polymer.

Class C fly ash• Fly ash produced from the burning of

younger lignite or sub bituminous coal, in addition to having pozzolanic properties, also has some self-cementing properties. In the presence of water, Class C fly ash will harden and gain strength over time.

• Class C fly ash generally contains more than 20% lime (CaO). Unlike Class F, self-cementing Class C fly ash does not require an activator. Alkali and sulfate (SO4) contents are generally higher in Class C fly ashes.

• At least one US manufacturer has announced a fly ash brick containing up to 50 percent Class C fly ash. Testing shows the bricks meet or exceed the performance standards listed in ASTM C 216 for conventional clay brick; it is also within the allowable shrinkage limits for concrete brick in ASTM C 55, Standard Specification for Concrete Building Brick.

• It is estimated that the production method used in fly ash bricks will reduce the embodied energy of masonry construction by up to 90%.

The re-use of fly ash as an engineering material primarily stems from its pozzolanic nature, spherical shape, and relative uniformity. Fly ash recycling, in descending frequency, includesusage in

• • Portland cement and grout• • Embankments and structural fill• • Waste stabilization and solidification• • Raw feed for cement clinkers• • Mine reclamation

•• Stabilization of soft soils•• Road sub base•• Aggregate•• Flowable fill•• Mineral filler in asphaltic concrete•• Other applications include cellular

concrete, geopolymers, roofing tiles, paints, metal castings, and filler in wood and plastic products.

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