• National Thermal Power Corporation (NTPC), a Maharatna CPSU under Ministry of Power and India’s largest integrated power producer, in its endeavour towards 100% utilization of fly ash has invited Expression of Interest (EOI) for sale of fly ash from the designated plants.


  • Fly ash is a byproduct from burning coal in electric power generating thermal power plants.
  • During combustion, mineral impurities in the coal fuse in suspension and float out of the combustion chamber with the exhaust gases. As the fused material rises, it cools and solidifies into spherical glassy particles called fly ash.
  • Fly ash is collected from the exhaust gases by electrostatic precipitators or bag filters
  • Composition
    • Fly ash particles are oxide rich and consist of silica, alumina, oxides of iron, calcium, and magnesium and toxic heavy metals like lead, arsenic, cobalt, and copper.
    • Major oxides are present are aluminium silicate (in large amounts), silicon dioxide (SiO2) and calcium oxide (CaO).
  • Fly ash pollutes air and water and may cause heavy metal pollution in water bodies.
  • Fly ash affects crops and vegetation as a result of its direct deposition on leaf surfaces.


  • Used in the manufacture of Portland cement.
  • Typically used for embankment construction.
  • Used as a soil stabilisation material.
  • Fly ash is also used as a component in the production of flowable fill.
  • Used as the filler mineral in asphalt road laying to fill the voids.
  • Fly ash is used as component in geoploymers.
  • Used in Roller compacted concrete dams.
  • Used in the manufacture of fly ash bricks
  • When flyash is treated with silicon hydroxide, it acts as a catalyst.


With reference to ‘fly ash’ produced by the power plants using the coal as fuel, which of the following statements is/are correct?

  1. Fly ash can be used in the production of bricks for building construction
  2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete
  3. Fly ash is made up of silicon dioxide and calcium oxide only and does not contain any toxic elements.

Select the correct answer using the code given below

  1. 1 and 2
  2. 2 only
  3. 1 and 3
  4. 3 only

Answer: a) 1 and 2

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