Abstract
Pozzolanic supplementary cementitious materials improve the long-term strength and durability of concrete systems by forming additional calcium silicate hydrate. ASTM C618, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, is a standard specification that covers coal fly ash and raw or calcined natural pozzolans; however, the two criteria in the standard intended to assess pozzolanicity are not sufficient and there are no existing ASTM standard test methods for directly measuring pozzolanicity. In this study, the accelerated mortar bar test for alkali-silica reaction (ASR) in ASTM C1567, Standard Test Method for Determining the Potential Alkali-Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar-Bar Method), and modified strength activity index (SAI) testing were tested in tandem to assess pozzolanicity of materials. Known inert materials and pozzolanic materials that qualify as Class N pozzolans and Class F fly ash in ASTM C618 were tested in accordance with ASTM C1567 to find replacement levels that successfully suppress ASR expansion below 0.10 %. The materials were then tested at the same replacement levels in a modified SAI test with a fixed water-to-cementitious materials ratio. The results from the two test methods were coupled to assess pozzolanicity of materials, with materials being classified pozzolanic only if they suppressed ASR expansion below 0.10 % and passed modified SAI testing over 75 % of control at the same replacement level. Neither of the test methods on their own can assess pozzolanicity accurately. However, the proposed method in this study successfully screened inert materials that qualify as Class N natural pozzolans and successfully identified pozzolanic materials.