Fly Ash

Fly ash is a fine, powdery substance that "flies up" from the coal combustion chamber (boiler)and is captured by emissions controls, such as an electrostatic precipitatororfabric filter "baghouse," and scrubbers.

This material is virtually identical in its composition to volcanic ash with pozzolanic properties ideal for concrete that built the structures of Ancient Rome we appreciate 2,000 years later. More than half of the concrete produced today in the U.S. uses fly ash in some quantity as a substitute for traditional cement. Among the world's most renowned bridges, skyscrapers, roads, dams, and a wide range of other construction projects were built using high-performance fly ash concrete mixes to achieve superior strength and longevity. Builders routinely use 40 percent fly ash mixes. That amount can reach 70 percent or more in massive walls, girders, dams, and foundations.

Among fly ash concrete's major environmental advantages:

  • Eliminates the need to mine virgin materials and thus prevents the associated impacts, while also conserving limited material resources;
  • Conserves land otherwise used for disposal;
  • Does not require kilning and therefore protects the atmosphere from carbon dioxide release; for every ton of fly ash used to replace traditional cement a ton of carbon dioxide is saved from entering the Earth's atmosphere; over the past decade fly ash recycling eliminated nearly a billion tons of greenhouse gas;
  • Conserves water because fly ash uses very little compared with traditional cement.

Besides concrete, fly ash is also used in composite materials, such as in aluminum metal alloys for lightweight auto parts and synthetic lumber for outdoor decks and fences.

Please visit www.coalashfacts.org for more factual information on fly ash and other coal combustion products.


  • Raw material in concrete products and grout
  • Feed stock in the production of cement
  • Fill material for structural applications and embankments
  • Ingredient in waste stabilization and/or solidification
  • Ingredient in soil modification and/or stabilization
  • Component of flowable fill
  • Component in road bases, sub-bases, and pavement
  • >Mineral filler in asphalt

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