Ground and Sieved Bio Ash versus Coal Fly Ash: Comparative Analysis of Pozzolanic Reactivity

Due to the declining availability of coal fly ash, there is a need to identify alternative sources of supplementary cementitious materials (SCMs). This article presents an investigation on the reactivity of ground and sieved bio ash that can be used as alternative sources of SCM. The oxide contents of bio ash are similar to Class-C coal fly ash. Accordingly, bio ash was found to have both hydraulic and pozzolanic reactivity. Ground bio ash showed higher heat of hydration and similar compressive strength compared to coal fly ash at the early stage (i.e., up to 7 days) of cement hydration due to the hydraulic reactivity. Grinding the bio ash improved its pozzolanic reactivity by 25% as per the modified Chapelle test. Using bio ash as SCM was also found to increase the ettringite formation in cement matrix. Nevertheless, the potential of excessive expansion of the paste samples due to the ettringite formation was found to be negligible.