Fluidity and strength behaviors of cemented foam backfill: effect of particle size distribution and foaming agent dosage.

The influence of aggregate gradation (11 gradations with volume moment mean diameter ranging from 192 to 398 μm) and hydrogen peroxide (HP) dosage (0%, 0.8%, 1.6%, 2.4%, and 3.2% by weight of cement) on the fluidity, strength, and microstructure of cemented foam backfill (CFB) was comprehensively evaluated in this study. The fluidity, expansion ratio, and water film thickness for fresh CFB and 28-day strength and microstructural properties for hardened CFB were compared as a function of aggregate gradation and HP dosage. The end results reveal that the fluidity of fresh CFB decreases with finer aggregate and higher HP dosage due to their effect on water film thickness, but the expansion ratio increases. The strength for hardened backfill without foaming agent increases with coarser aggregate, but that for cemented foam backfill decreases. Additionally, the mercury intrusion porosimetry (MIP) results denote that the variation of aggregate gradation and HP dosage mainly influences the volume of large pores (>1 μm) and consequently the overall porosity of CFB, resulting in the strength variation. The linear relationship between compressive strength and averaged fractal dimensions of cross-sections obtained from X-ray CT indicates that the number of extra-large pores (100~500 μm) determines the strength of CFB. The influence of HP on the hydration reaction of backfill and the potential application of CFB in mining practices are also discussed. [ABSTRACT FROM AUTHOR]