Slag or Other Supplementary Materials?


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Title: Slag or Other Supplementary Materials?

Author(s): Robert E. Philleo

Publication: Special Publication

Volume: 114


Appears on pages(s): 1197-1208

Keywords: blast furnace slag; economics; fly ash; properties; silica fume; specifications; Materials Research

Date: 5/1/1989

Supplementary materials have similar effects on concrete but differ in many respects including composition, geographical distribution, amount of processing required, properties, economics, method of use, and specification requirements. Blast furnace slag is a cementitious material that reacts directly with water in the presence of an activator. In the absence of a chemical activator, calcium hydroxide produced in the hydration of portland cement serves as the activator. The other common supplementary materials, fly ash and condensed silica fume, are pozzolans, which require calcium hydroxide a necessary reactant in the pozzolanic reaction. High-calcium fly ash is cementitious and pozzolanic. Natural pozzolans and rice husk ash are acceptable materials not in widespread use. Condensed silica fume is a premium product for uses such as high strength, low permeability, and high electrical resistivity. Fly ash and blast-furnace slag have the potential to reduce the cost of concrete and to provide such benefits as reduced heat of hydration, resistance to sulfate attack, and inhibition of the alkali-aggregate reaction. Blast-furnace slag provides the greatest energy savings in that it may be used with little or no portland cement. Alkali-activated slag can also be made to hydrate at low temperatures.