Fly Ash

Fly ash is a pozzolanic admixture for concrete, consisting of the "finely divided residue that results from the combustion of ground or powdered coal" as defined by ASTM C 618. Coloring varies from light gray to buff, depending on the type of coal burned and the conditions of combustion. As a pozzolan defined by ASTM, fly ash reacts chemically with calcium hydroxide produced by the hydration of portland cement to form additional cementitious compounds. When properly designed, concrete containing fly ash will deliver equal 28 day strengths and continue to increase compared to plain portland cement concrete.

Class F fly ash increases the ability of concrete to resist attack from sulfates in soil or groundwater and potentially disruptive alkali-aggregate reaction. It is produced from the combustion of pulverized bituminous or Texas lignite coal.

When designing concrete mixtures, fly ash is normally considered part of the cementitious content. As such, current technology favors optimizing its use as a discrete raw material. This fly ash may be used as a separate concrete addition, a partial replacement for portland cement, and a partial replacement for portland cement and as an addition.

Boral Material Technologies Inc., 45 NE Loop 410 Suite 700, San Antonio, TX 78216. Tel: 210-3494069; Fax: 210-349-8512.