An Enhanced Procedure to Measure Strength and Durability of Pozzolans

The current ASTM C311 test method to determine strength activity index (SAI) of fly ash and pozzolans was introduced in the 1980s. ASTM C618 specifies that a fly ash or pozzolan should have a minimum SAI of 75%. The SAI limit is inadequate because marginal materials, which are neither pozzolanic nor partially cementitious materials, are known to meet the 75% limit. A strength efficiency test procedure is proposed to replace the current SAI test. Strength efficiency of a fly ash or pozzolan is subdivided into efficiency from chemical reaction (pozzolanic and cementitious) and efficiency from changes in water-cement ratio (non-chemical impacts). A new specification limit is proposed based on chemical efficiency In turn, chemical reaction is subdivided into pozzolanic and self-cementing reactions, which coincides with the recent 18% CaO% specification that separates Class C and Class F fly ashes.