Fly Ash

Fly ash is the finely divided residue that results from the combustion of pulverized coal and is transported from the combustion chamber by exhaust gases. At present, over 20 million metric tons (22 million tons) of fly ash are used annually in a variety of engineering applications. Fly ash is most commonly used as a pozzolan in Portland Cement Concrete (PCC) applications. Pozzolans are siliceous or siliceous and aluminous materials, which in a finely divided form and in the presence of water, react with calcium hydroxide at ordinary temperatures to produce cementitious compounds.
The unique spherical shape and particle size distribution of fly ash make it a good mineral filler in Hot Mix Asphalt (HMA) applications and improves the fluidity of flowable fill and grout. The consistency and abundance of fly ash in many areas present unique opportunities for use in structural fills and other highway applications.