A new approach to measuring pozzolanicity of Supplementary Cementitious Materials using existing ASTM standards

Supplementary cementitious materials (SCMs) improve the long-term strength and durability of concrete systems through the pozzolanic and/or hydraulic reactions that form additional calcium silicate hydrate (C-S-H) phases. SCMs come in various shapes and forms, and ASTM C618 provides a standard specification that covers coal fly ash and raw or calcined natural pozzolans. However, the two main criteria outlined by the standard, sum of oxides and strength activity index (SAI), are not sufficient for indicating pozzolanicity of materials; and existing test methods for measuring reactivity or pozzolanicity are yet to be standardized. Due to these existing problems, the accelerated mortar bar test (AMBT) outlined by ASTM C1567 and modified SAI testing were implemented in tandem to assess pozzolanicity of materials. Known inert materials and pozzolanic materials that qualify as Class N pozzolans and Class F fly ash were tested per ASTM C1567 to find replacement levels that suppress ASR expansion below 0.10%. Then the same materials were tested at same replacement levels for modified SAI with a fixed water-to-cementitious materials ratio (w/cm) using cylindrical specimens. The data from the two test methods were compared and compiled to assess pozzolanicity. Materials that successfully suppressed ASR expansion below 0.10% and passed modified SAI testing over 75% of control were classified as pozzolanic materials. The proposed method of the thesis successfully screened inert materials that qualify as Class N pozzolans, and successfully identified pozzolanic materials.