Abstract
ASTM C618 and AASHTO M 295 specifications for fly ash represent the primary documents used by U.S. state and federal agencies to determine the suitability of a fly ash source for use in concrete. Other countries have broadly similar specifications for fly ash. The article compares specifications from the United States, Canada, Europe, Australia, and New Zealand, noting similarities and differences. Despite its common use, several criticisms of the ASTM C618 specification exist and are discussed in this document. Specifically, concerns exist regarding its dependence on strength activity index testing for determination of fly ash reactivity and strength generation potential, and loss on ignition for quantification of unburnt carbon content, as these tests relate somewhat poorly to performance of the fly ash in concrete. Recently developed test methods that could improve some of the most problematic components of the ASTM C618 specification are discussed.
