Fly Ash

Fly ash is a fine powder generated by the burning of pulverised coal in electric power plants. It is a pozzolan, a substance combining aluminous & siliceous material that makes cement when mixed with water. When combined with water and lime, fly ash produces a chemical that is comparable to Portland cement. Fly ash can be used as a primary component in mosaic tiles, hollow blocks, and blended cement, among many other construction materials. Fly ash improves the segregation and strength of concrete and makes it easier to pump when added to concrete mixes.

Meaning of Fly Ash

Fly ash is a thin grey powder made up primarily of spherical, glassy molecules, a byproduct of coal-fired power plants. Pozzolanic qualities refer to the ability of fly ash to react with lime to produce cementitious compounds. Fly ash has a wide range of applications and uses, including the following:

• Dams
• Concrete
• Mines
• Geopolymer concrete
• Flowable fill
• Landfills

Fly ash is a combustion waste made up of tiny particles that ascend with the flue gases. Bottom ash is a type of ash that does not rise. Fly ash is the ash formed during coal burning in an industrial setting. The material fly ash is heterogeneous. Electrostatic precipitators absorb fly ash debris that solidifies while suspended in exhaust gases. Fly ash particles are generally spherical and range from 0.5 m to 300 m since they harden quickly while suspended in exhaust fumes. Fly ash increases the performance of concrete and has various applications in both cement and non-cement industries. The main chemical components present in fly ash are:

• Silicon dioxide
• Calcium oxide
• Ferric oxide
• Aluminium oxide

Uses of Fly Ash

Portland Pozzolana Cement (PPC): Portland Pozzolana Cement is made by mixing fly ash with Portland cement. It is used in various construction works.

Fly Ash Concrete: Fly ash is used in concrete to replace Portland cement. It can replace up to 30 per cent of the Portland cement by mass, although it can be utilised at a more percentage in particular applications. In certain circumstances, fly ash improves the final strength, durability and chemical resistance of concrete. Fly ash could be used as a partial replacement for sand and cement in concrete to increase workability, minimise hydration heat, and the impermeability of  concrete or sulphate attack resistance. Fly ash in concrete can be used if its qualities are within specific limits, but particle size classification and control of unburned coal considerably boost the fly ash’s favourable effects.

Embankments: Fly ash is also utilised to build embankments because of its high homogeneity coefficient and clay-sized particles. The usage of fly ash in embankments is influenced by compaction characteristics, permeability, grain size distribution, shear strength, compressibility, and frost susceptibility.

Types of Fly Ash

Fly ash is divided into Class C and Class F. Particles covered in melted glass are found in Class F fly ash. Sulphate attack, which can develop in fertilised soils and near coastal areas, is considerably reduced. Class F is low in calcium and has a carbon level of less than 5% in most cases. Class C fly ash is also chemically resistant to expansion. It is more typically used for structural concrete because it contains a higher amount of calcium oxide than Class F. Class C fly ash is generally made of high-calcium fly ashes with less than 2% carbon content. Fly ash is used in more than half of all concrete in the United States. Dosage rates differ based on the type of fly ash used and its amount of reactivity. Class F fly ash is typically utilised at dosages of 15% to 25% by mass of cementitious material, while Class C fly ash is used at dosages of 15% to 40% by mass of cementitious material.

Conclusion

In this article, we have discussed the meaning of fly ash, its uses and its types. Fly ash comprises small particles of burned fuel and flue gases that are forced out of coal-fired boilers. Fly ash is a multipurpose material that may be used for various applications. Its use is dependent on local conditions, and it can be used in a variety of ways for various goods. Within a 50-kilometre radius of coal or lignite-based thermal power plants, the Indian government has published rules requiring at least 25% ash in the manufacture of clay bricks, blocks, or tiles.