Effect of nano-SiO2 on mechanical properties, fluidity, and microstructure of superfine tailings cemented paste backfill

The application of solid waste filling has emerged as the principal means of achieving cleaner production in mines, due to its substantial environmental benefits. To efficiently utilize superfine tailings, a series of experiments are conducted to investigate the effect of nano-SiO2 (NS) on the performance characteristics of superfine tailings cemented paste backfill (SCPB). The findings indicate that the yield stress, viscosity, and thixotropy of SCPB slurry increase with increasing NS dosage, while the slump flow of SCPB slurry decreases. The uniaxial compressive strength (UCS) of SCPB shows an increasing trend followed by a decreasing trend with rising NS dosage, and reaches its peak at an NS dosage of 1%. NS has a pronounced impact on the early UCS, but only a moderate influence on the mid to late UCS of SCPB. Microanalysis results suggest that NS particles have a strong tendency to agglomerate with each other, and the inability of NS agglomerates to fill the interstitial voids between solid particles curtails the slurry's fluidity. During the early stage of the hydration reaction, NS's volcanic ash effect accelerates cement hydration and exerts a catalytic effect on gypsum, resulting in an increase in products such as C-S-H gels and ettringite crystals. In addition, the C-S-H produced by the use of NS exhibits a decreased Ca/Si ratio and a more robust molecular configuration. This is the fundamental reason why NS has a significant impact on the early UCS. The outcomes of this study can provide crucial direction for the effective utilization of superfine tailings.