Abstract
Aiming at the utilization of regional mining wastes including iron tailings sand and coal gangue (CG), a novel coal gangue-filled backfill (CGFB) is proposed in this paper, which is achieved by casting the self-consolidating cement-tailings grout (CTG) into pre-placed CGs skeleton. The mixture proportions of self-consolidating CTGs were first designed based on the rheological properties by adding viscosity enhancing agents (i.e. hydroxypropyl methylcellulose and polyacrylamide) and polycarboxylate superplasticizer (PCE). As a consequence, the static stabilities and filling abilities of fresh CTGs were also strengthened. The filling ability of fresh CTGs is a flowability-related parameter and can be reflected by the surface bugholes of hardened CGFBs. The results indicate that the use of CTG with flow diameter > 25 cm and flow time < 15 s is suitable for filling voids in pre-placed CGs skeleton. With the use of optimized self-consolidating CTGs with high W/C ratios (i.e. 1.0 and 1.2) and mass fraction of 70%, CGFBs show advantages in strengths and strength efficiencies over the conventional cemented tailings backfills. Moreover, owing to the utilization of high-volume solid waste, CGFBs bring benefits of low costs and low environmental impacts.
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