Influence of coal bottom ash aggregate grading on properties of GGBS binary blended cement mortar

The effect of different coal bottom ash (CBA) gradings on ground granulated blast furnace slag (GGBS) binary blended cement mortar is not well-documented in current literature. Therefore, previous studies have reported inconsistent and contradictory effects of using various CBA gradings as a fine aggregate replacement in mortar and concrete. Hence, the present work aimed to establish the influence of different coal bottom ash (CBA) gradings, which is crucial for reducing coal power plant waste by utilising larger fractions of CBA in mortar and concrete without compromising its hardened properties. Specifically, this study investigated the optimal grading of coal bottom ash (CBA) for natural sand replacement in ground granulated blast furnace slag (GGBS) binary blended cement mortar. The research examines three CBA gradings: passing 10 mm sieve (R-CBA), passing 4.75 mm sieve (S-CBA), and grading according to BS EN12620 (Gr-CBA) at 20 %, 40 %, and 60 % sand replacement levels for comparison. Resultant mortar specimens were tested at 7, 28, and 91 days for mechanical strength, fluid transport, and drying shrinkage. Results show that all CBA gradings performed better than the control mix (with river sand only). The Gr-CBA mix outperformed the S-CBA mix by up to 29 % in strength due to highly consistent grading. R-CBA mix exhibited optimal performance compared to the other two CBA mix up to 30 % in strength. The coarser grading of the R-CBA mix enhances the interfacial transition zone and aggregate-binder bond and, hence, exhibited a better performance. This study highlights the potential use of R-CBA grading to increase the CBA reuse rate in mortar or concrete while maintaining desirable performance.