Performance optimization and characterization of loess-slag-based geopolymer composite: A new sustainable green material for backfill

[Display omitted] •Cemented backfill preparation with loess and slag.•Effect of loess percentage on workability of the cemented backfill.•Effects of loess percentage and curing time on failure modes.•Coupling effects of loess percentage and curing time on strength and microstructure.•The optimum ratio for loess to slag of the cemented backfill. Recycling idle materials and industrial solid wastes to prepare cemented backfill is one of the best ways to achieve green mining. In this study, we synthesized a loess-slag-based geopolymer composite (LSGC) by utilizing loess and slag (ground granulated blast-furnace slag) as cementing materials, sodium silicate as an alkaline activator, and recycled waste sandstone as aggregates. Through the tests of uniaxial compression, scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS), the workability and setting time, uniaxial compressive strength (UCS), and the microstructure characteristics with the coupling effect of curing time (t) and loess percentage (LP), as well as the best loess slag ratio were finally determined. The results indicate that the increase in LP can enhance the workability and the setting time of LSGC paste. The UCS of LSGC increases with curing time, with the greatest rise occurring during the first three days, and it is negatively correlated with LP. The loess gel in LSGC is sodium-aluminate-silicate-hydrate (N-A-S-H), while the slag gel is calcium-(aluminate)-silicate-hydrate (C-(A)-S-H). Finally, it is revealed that 1:1 is the optimum ratio for loess to slag. At this ratio, the workability and setting time of LSGC are qualified, the 28-day UCS is about 14.61 MPa, and the microstructure is dense and stable. This study is of great significance in promoting the recycling of idle materials and industrial solid wastes as well as green backfill mining.