Strength and microstructure evolution in cemented mine backfill with low and high pH pyritic tailings: Effect of mineral admixtures

To properly dispose mining-induced tailings, diverse techniques including cemented paste fill (CPB) have been already employed. Indeed, tailings are manufactured by using different admixtures which are poisonous to the environment and need to be closely explored by considering its effects. This study dealt with the quality of CPB containing low pH (4.9) and high pH (10.8) pyritic tailings. Besides, employing ground blast furnace slag (GBFS) and fly ash (FA) in diverse rates instead of ordinary Portland cement (OPC) and their effects on fill performance were explored. Strength and microstructure of CPB made with constant solid content (72 wt%) and different OPC/GBFS-FA ratios (e. g., 90/10, 70/30 and 50/50) were carried out by several laboratory tests. Results showed that the lowest UCS performance was obtained from CPB having 50%FA and acidic tailings. It was also observed that GBFS-based backfills gave better strength than FA-based ones, irrespective of tailings, owing to the former’s high pozzolanic activity and grain shape. Regardless of additives, the highest strengths were gained from basic tailings-based backfills. pH of pyritic tailings affected fill’s performance due to its aggressive effects on cement hydration. To sum up, this study has provided relevant information and technical evidence that will subsidize the engineering design of a low-cost, zero-waste, and viable mine fill system.