Assessment of rheological parameters of high density cemented paste backfill mixtures incorporating superplasticizers

The addition of superplasticizers or high-range water reducers (HRWRs) to high density cemented paste backfills (CPBs) can improve their rheological behavior and facilitate pumping operations. This study aimed to assess the influence of various mixture parameters, including HRWR type and dosage, binder type and content, as well as tailings characteristics on the rheological properties of CPB mixtures. CPBs were formulated at a solid mass concentration of 80% with two types of tailings (T1 and T2) and three types of binders, including a general use Portland cement (GU), a blended binder (S-GU) comprising 80% ground granulated blast furnace slag and 20% GU, and another blended binder (GU-FA) comprising 50% class F fly ash and 50% GU. Five different types of HRWRs, including three polycarboxylate-based (PC), one polymelamine-based (PMS), and one polynaphtalene-based (PNS), were assessed. Results showed that HRWR addition to CPB reduced the rheological parameters, including yield stress, flow index, and infinite shear viscosity. Furthermore, the rheological behavior changed from shear thickening for control CPB to Binghamian with increasing HRWR dosage. The optimum PC dosage of 0.121% (by dry mass of total CPB solids) can ensure a CPB with yield stress lower than 200 Pa, which has been reported as the upper limit for effective centrifugal pumping of CPB. The PC-type HRWRs were more efficient than the PMS and PNS types. Superplasticized CPB mixtures made with S-GU and GU-FA binders exhibited better rheological properties than those using GU binder. Binder content ranging from 3.5 to 6% appeared to have a negligible effect on the performance of the PC-type HRWRs.