Effects of fly and coal bottom ash ratio on backfill material performance

Fly ash (FA) and coal bottom ash (CBA) were selected to study the effects of their ratios on backfill materials. The rheological properties, stability, mechanical properties, crystal structure, and microstructure of backfill materials were investigated at different FA/CBA ratios. Increased FA/CBA values improved the slump, rheological performance, setting time, mechanical strength, and elastic modulus. However, the excellent water retention of CBA reduced the bleeding capacity, and the alkali-activated reaction by CBA generated a large amount of ettringite (AFt) that produced early strength. In the late period, the FA/CBA values affected the morphology and compactness of the calcium-silicate-hydrate gels. Furthermore, the performance of backfill materials with 0.5% superplasticizer and 30%-50% FA/CBA ratio could satisfy the requirements, and this formula has been applied to the filling mining project.