Admixture Effects on the Rheological/Mechanical Behavior and Micro-Structure Evolution of Alkali-Activated Slag Backfills

Recently, alkali-activated slag (AAS) has attracted extensive attention in cemented paste backfill (CPB) due to its low cost/CO2 emissions and high strength benefits. However, a comprehensive analysis of the mechanical/rheological behavior and microstructure evolution of AAS-CPB using mineral admixtures is still lacking. In this study, metakaolin (MK), fly ash (FA), and silica fume (SF) were employed to replace ground granulated blast furnace slag (GGBS) at various levels to formulate an alkali-activated binder, and the corresponding mechanical, rheological, and microstructure properties of CPB were investigated. The results suggest that FA tends to reduce CPB’s rheological and strength evolution and this negative effect increases with the FA dosage. The replacement of MK or SF increases the rheological parameters and thus diminishes fluidity and has positive or negative effects on strength depending on the replacement level and curing age. This study’s findings will contribute to developing a new scheme for lucrative and environmentally responsive multi-solid waste-based AAS-CPB in the field.