Statistics compiled by the National Ash Association, Inc. show that in 1983, 52.35 million tons of fly ash were produced in the United States and only 3.62 million tons were used for raking cement and concrete products. The low rate of utilization of fly ash as a supplementary cementing material in the cement and concrete industries has partly been attributed to the lack of quality control. For an effective quality control on fly ash suitable for use as a pozzolan, it is necessary to know which of the numerous physical and chemical characteristics of the material greatly influence the behavior of Portland cement-fly ash mixtures, such as the rate of strength development. There is general agreement that standard test methods currently in use, e.g., the ASTM C 311 Pozzolan Activity Test, dc not provide a useful measure for evaluation of relative reactivity of fly ashes from different sources.