Title: An Enhanced Procedure to Measure Strength and Durability of Pozzolans
Author(s): Edwin R. Dunstan Jr.
Publication: Materials Journal
Appears on pages(s): 183-192
Keywords: alkali-silica reaction; chemical reaction; durability; fly ash; pozzolan; pozzolanic reaction; self-cementing reaction; strength; sulfate resistance
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.