Compatibility of modified magnesium slag-based backfill materials to polycarboxylate superplasticizer: flow, water-film thickness and strength

Fluidity influences the use of backfill materials in the mining industry. A new backfill material—modified magnesium slag-based backfill materials (MFPB)—is made from solid waste from coal and metallurgy. We focus on the compatibility of polycarboxylate water reducing agent (SP) with MFPB and its effect on MFPB performance. The results indicate that: (ⅰ) The Hershel–Bulkley explains the rheological behavior of MFPB slurry, and the rheological parameters of MFPB are greatly impacted by addition of SP. (ⅱ) SP content, both yield stress and viscosity of the MFPB slurry decrease and are lowest at 0.4% SP content. (ⅲ) Rheological and slump experimental results indicate that SP improves MFPB fluidity. By decreasing the basic water requirement of MFPB, raising slurry free water content, water film thickening, and postponing development of flocculated structures in MFPB, SP enhances the fluidity of MFPB. (ⅳ) Microscopic tests (thermogravimetric-derivative thermogravimetry and scanning electron microscopy) demonstrated that the primary reason for the variations in the uniaxial compressive strength of MFPB was the detrimental impact of SP on the flocculated structure. We report the mechanism by which SP influences MFPB performance, and examine the compatibility between SP and MFPB from the perspectives of water film thickness and other factors. The results of this study references for creating high-fluidity MFPB are made. [Display omitted] •Fresh MFPB slurry with the addition of polycarboxylate water reducer (SP) conforms to the H-B model.•SP increases the fluidity of MFPB and decreases the yield stress.•SP molecules have a delayed generation and disruption effect on the flocculated structure in MFPB.•SP increases the WFT of particles in the MFPB and weakens the inter-particle gravity.•The MFPB slurry's slump, extension, and yield stress are all correlated with WFT.