The effect of coarse aggregate on the bleeding and mechanical properties of cemented paste backfill粗骨料对膏体泌水性及力学性能的影响

An experimental study is conducted to investigate the effect of different aggregate types, coarse aggregate content, mass concentration, and cement-sand ratio on the bleeding rate and mechanical properties of cemented paste backfill (CPB). Replacing river sand with unclassified tailing can significantly reduce the bleeding rate. The addition of fine-grained tailing increased the water retention of the mixture by 10%–20% and the 28 d unconfined compressive strength (UCS) by 10%–30%. The sensitivity of the bleeding rate to mass concentration is reduced at 60% coarse aggregate content. Increasing the coarse aggregate content is a way to improve the high-concentration CPB fluidity. There is a coarse aggregate optimal content to maximize the sample strength. Test results show that when the coarse aggregate content is 50%, the maximum CPB strength can reach 6.5 MPa. As the mass concentration increases, the mechanical properties increase proportionally. After curing 28 d, the UCS of the 79% mass concentration sample reached 7.9 MPa. The cement-sand ratio had a greater effect on the mechanical properties, and when the cement-sand ratio increased from 1:6 to 1:4, the UCS at 28 d increased by 54.4%, and the bleeding rate decreased to 1.4%.