Fly Ash

Last updated: September 9, 2019

What Does Fly Ash Mean?

Fly ash is a fine gray powder consisting mostly of spherical, glassy particles that are produced as a byproduct in coal-fired power stations. Fly ash has pozzolanic properties, meaning that it reacts with lime to form cementitious compounds. It is commonly known as a supplementary cementitious material.

Fly ash is suitable for a wide variety of applications and uses, including:

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

Fly ash is also known as flue-ash or simply ash.


Corrosionpedia Explains Fly Ash

Fly ash is a residue generated in combustion and comprises the fine particles that rise with the flue gases. Ash that does not rise is called bottom ash. In an industrial context, fly ash usually refers to ash produced during combustion of coal. Fly ash is a heterogeneous material. The main chemical components present in fly ash are:

  • Silicon dioxide
  • Aluminum oxide
  • Ferric oxide
  • Calcium oxide (occasionally)

Fly ash material solidifies while suspended in the exhaust gases and is collected by electrostatic precipitators or filter bags. Since the particles solidify rapidly while suspended in the exhaust gases, fly ash particles are generally spherical in shape and range in size from 0.5 µm to 300 µm.

Fly ash significantly improves concrete performance and also provides many benefits in cement and non-cement applications. Also, when treated with sodium hydroxide, fly ash appears to function well as a catalyst for converting polyethylene into a substance similar to crude oil in a high-temperature process called pyrolysis.





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