pulverised fuel ash FLY ASH

Uses, Benefits and Drawbacks of Fly Ash in Construction

concrete curb construction

Updated April 07, 2017
Fly ash is a fine powder which is a byproduct from burning pulverized coal in electric generation power plants. Fly ash is a pozzolan, a substance containing aluminous and siliceous material that forms cement in the presence of water. When mixed with lime and water it forms a compound similar to Portland cement.

The fly ash produced by coal-fired power plants provide an excellent prime material used in blended cement, mosaic tiles, and hollow blocks among others.


Fly ash can be an expensive replacement for Portland cement in concrete although using it improves strength, segregation, and ease of pumping concrete. The rate of substitution typically specified is 1 to 1 ½ pounds of fly ash to 1 pound of cement. Nonetheless, the amount of fine aggregate should be reduced to accommodate fly ash additional volume.

Fly Ash Applications
Fly ash can be used as prime material in blocks, paving or bricks; however, one the most important applications is PCC pavement. PCC pavements use a large amount of concrete and substituting fly ash provides significant economic benefits. Fly ash has also been used for paving roads and as embankment and mine fills, and it's gaining acceptance by the Federal government, specifically the Federal Highway Administration.

Fly Ash Drawbacks
Smaller builders and housing contractors are not that familiar with fly ash products which could have different properties depending on where and how it was obtained.

For this reason, fly ash applications are encountering resistance from traditional builders due to its tendency to effloresce along with major concerns about freezethaw performance.

Other major concerns about using fly ash concrete include:

Slower strength gain.
Seasonal limitation.
Increase in air entraining admixtures.