Evaluation of a dry FGD material as a flowable fill

Many flue gas desulfurization (FGD) materials have low unit weight and good shear strength characteristics and thus hold promise for flowable fill applications. This paper focuses on the potential of using spray dryer FGD ash in flowable fill as a replacement for conventional fly ash. Several design mixes were considered. The design mixes consisted of varying amounts of FGD, cement, lime, admixture, and water. The mixes were tested in the laboratory for flowability, unit weight, moisture content, unconfined compressive strength (UCS), erodibility, set time, penetration, and long-term strength characteristics. Tests were conducted for up to 90 days of curing. The FGD flowable fill without any additives was observed to be comparable to regular (normal set) flowable fill in terms of placeability, UCS, and ‘diggability’. FGD flowable fill with additives and admixtures compared favorably with the characteristics of conventional quick-set flowable fills.