Expansion and strength properties of cemented backfill using sulphidic mill tailings

The expansion and strength properties of cemented tailings backfill (CTB), especially prepared from sulphidic mill tailings, are valuable for the estimation of design parameters for underground stope filling as well as for numerical simulation. In this paper, the effect of the curing time, sulphur content, cement dosage and solids concentration effect on the free expansion ratio (FER) of CTB specimens was investigated using an invented lab apparatus called (free expansion measuring instrument). And the relationship between the FER and the unconfined compressive strength (UCS) was analyzed. And then, mineralogical composition of CTB samples was tested by X-ray diffraction. The backfill recipe (sulphur content, binder dosage and solids concentration) and curing days had significant influences on the expansion performance. The research results indicated that with the increase of sulphur content, the FER showed no obvious growth at the curing of 28 days. However, after 120 days, FER increased from 4.856% (S: 3.64 wt%) to 9.613% (S: 20 wt%). As the solids concentration increased, the FER also rose. And this growth was distinctive only when the solids concentration is relative high (65-75 wt%) and at the long-term curing time (120 days). The proportions of binder and the obtained FER clearly showed a sub-linear and proportional relationship. Increasing the amount of binder (8-16 wt%) cannot restrict the increment of expansion ratio, and ultimately the specimens would generate cracks and collapse. Meanwhile, there was a significant negative correlation between the UCS and the FER from the same group of specimens. When the FER reached a certain value, the strength value dropped sharply.