Study on the Mechanism of Nano-SiO2 Affecting the Strength of Cement Paste Backfill

The strength of cement paste backfill (CPB) is crucial for ensuring the safe and efficient operation of the horizontal layered approach backfill mining method. To effectively improve CPB strength, a series of experiments were carried out to systematically examine the effects of nano-SiO2 (NS) on the mechanical properties, hydration process, setting time, and microstructure of CPB. The results show that at a content of 1.5%, NS fully utilizes its pozzolanic, filling, and nucleation effects, accelerating cement hydration, filling internal pores, and thereby increasing matrix density and CPB strength. Conversely, at 2.5%, severe agglomeration of NS into large-sized aggregates weakens these three effects of NS, increases specimen porosity, reduces matrix density, and consequently impairs the mechanical properties of CPB. This study clarifies the mechanism by which an appropriate amount of NS improves CPB mechanical properties, as well as the intrinsic reasons for the performance degradation caused by NS overdosage. The findings provide a theoretical basis and experimental support for the rational application of NS in mine backfill.