Strength and fluidity of cemented paste backfill at Qijiaojing Iron Mine, Northwest China

Abstract

Open stope mining with sequent backfilling was the major method adopted at Qijiaojing Iron Mine, and mix proportions of backfill materials were performed to produce the industrially required cemented paste backfill (CPB). The materials mainly comprise unclassified extra-fine tailings, waste rocks and Portland cements, and the experiments of the mix proportions followed the L16 (4 5) orthogonal design. The results showed that contents of-20 and-37 μm extra-fine grains within tailings accounted for 54 and 69wt%, respectively. The range analysis of orthogonal experiments shows that mass concentration, tailing-waste ratio and wastecement ratio are the most to least sensitive factors to the slurry slump, 3-day and 7-day strengths. For 28-day strength, the sensitive variables are sequentially mass concentration, waste-cement ratio and tailing-waste ratio. Additionally, the optimal mix proportion for cement paste backfill is obtained with a mass concentration of 78wt%, a tailing-waste ratio of 0.7 and a waste-cement ratio of 25. The slump and 28-day strength of the optimal CPB are 25.2 cm and 1.29 MPa, respectively.