Abstract

Fly ash has been used as a pozzolanic admixture in concrete for more than 50 years. Earlier uses were largely confined to low-calcium ashes from hard bituminous or anthracite coals. However, increased demand for fly ash coupled with the declining availability of suitable low-calcium ashes has attracted a wider variety of fly ashes to the marketplace in recent years. Some of these ashes are characterized by very high calcium contents (for example, >25% CaO) and such materials affect the properties of concrete in a different manner than “traditional” fly ashes. The latest Canadian Standard covering fly ash for use in concrete divides fly ash into three categories strictly on the basis of its calcium content. This paper provides a rationale for this change in concept.

Issue Section:
Research Papers
Keywords:
calcium, classification, concrete, durability, fly ash, pozzolan, strength

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