Fly Ash is the most widely used SCM in concrete.  It is a is a fine powder that is byproduct of coal combustion in electric power generating plants and is created when the mineral impurities in the coal fuse together as they come out of the combustion chamber, then cool down and harden.

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, fly ash forms a compound similar to Portland cement. When used in concrete mixes, fly ash improves the strength and segregation of the concrete and makes it easier to pump.

Why Use Fly Ash?

• Fly ash's properties improve the performance of concrete.
• Concrete made with fly ash tends to be harder, has less cracks, less porous and gives off less dust.
• Fly ash requires less water than Portland cement and is easier to use in cold weather.
• It's highly impermeable and resistant to the ingress of water, chlorides and oxygen.
• The use of fly ash in concrete can contribute to LEED points through local materials, recycled contents and innovation credits.
• Fly ash reduces the environmental footprint of concrete. By replacing a portion of the cement used in the mix, fly ash reduces the green house gas emissions attributable to the application.
• It's a recycled material.