Abstract
The rheological properties (yield stress, flow index and infinite dynamic viscosity) and mechanical properties (unconfined compressive strength, UCS) of different cemented paste backfill (CPB) recipes must be determined during the laboratory optimization phase. However, the influence of the mixing procedure on these properties has scarcely been studied so far. The objective of this paper is to assess to what extent these properties depend on the specific mixing energy (SME) for a given type of mixer. CPB recipes were prepared based on two types of tailing (CPB-T1 and CPB-T2, also referred to as T1 and T2) at a fixed solid percentage for each type of tailing using the Omcan laboratory mixer. A mixture of 80% slag and 20% GU was used as a binder. The mixing time and the rotation speed of the mixer were successively varied. For each recipe prepared, we determined the SME, the rheological properties of fresh CPB (at the end of mixing) and the UCS at 7, 28 and 90 days of curing. The results show that yield stress and infinite viscosity decreased when SME increased in an interval going from 0.3 to 3.8 Wh/kg and 0.6 to 6 Wh/kg for CPB-T1 and CPB-T2, respectively. An increasing trend in UCS with increasing SME was also observed. Empirical equations describing the change of the rheological properties with the SME are used to estimate the change in rheological properties of CPB along the distribution system, considering the specific energy dissipation during CPB transportation. A mixing procedure for obtaining CPB mixtures that are representative of CPB deposited in underground mine stopes is suggested for laboratories who currently use a same mixing procedure, irrespective of the variable field specific energy.
Highlights
IntroductionThe reuse of mine tailings in cemented paste backfill (CPB) to fill excavations left by the extraction of mineral resources has become a common practice used widely in underground mines
The downward flow curves obtained by varying the mixing time from 5 to 30 min are presented in Figure 2a,b for cemented paste backfill (CPB)-T1 and CPB-T2, respectively
This paper assesses the individual effects of mixing parameters on the rheological and mechanical properties of CPB prepared with two mixing onand the CPB-T2), rheological mechanical
Summary
The reuse of mine tailings in cemented paste backfill (CPB) to fill excavations left by the extraction of mineral resources has become a common practice used widely in underground mines. The binder types used in the CPB were reviewed by [6]. General use Portland cement (Type GU) is often used in the mining industry as a binder. CPBs containing only this type of cement as a binder can, be vulnerable to internal sulphate attack, which destabilizes the mechanical integrity of the CPB matrix, especially in the presence of sulfidic tailings or mixing water containing high concentrations of sulphate ions [7]. Knowing that the portlandite (the hydrate responsible for the sulphate attack) released during hydration reactions can be consumed during pozzolanic reactions, 4.0/)
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