Reactivity and Reactivity Tests for Unconventional Fly Ashes

The use of supplementary cementitious materials (SCMs) is critical for sustainable and durable concrete. However, supplies of conventional SCMs are running out, which necessitates the use of unconventional fly ashes and other novel SCMs. A critical first step in their usage is the development of accurate and appropriate reactivity tests and a more detailed understanding of material reactivity. The standard ASTM C311 strength activity index test is a flawed test because of the early testing ages, filler effect, variable water-to-cementitious ratio, and low sensitivity of strength to reactivity. The recently standardized ASTM C1897 R³ reactivity test provides major advantages compared to other reactivity tests, however, it is expensive. The objectives of this dissertation are two-fold. The first is to better understand the reactivity of unconventional fly ashes including after size fractionation using multiple test methods. The second is to develop alternative reactivity tests for unconventional fly ashes that are cheaper or easier to use than the R³ test. It is shown that while all fly ashes are reactive, kinetic corrections are needed when using the R³ test. Reactivity increases in the finer size fractions, however, effects are specific to each fly ash. A cheap reactivity test based on furnace and balance was developed, as was a sensitive “bulk resistivity index” test. Both tests have standardization potential although further work is needed.