37 Figure 2 – XRD analyses of Cerro Lindo tailings Figure 3 – PSD Cerro Lindo tailings 3.3 Laboratory mix design programme A structured laboratory programme was developed using Cerro Lindo tailings and the same sulphate-resistant cement as in the plant. According actual CPB plant production, the programme compared a baseline typical mix (no admixture) against mixes containing a tailormade polymer admixture for paste backfill. The admixture is a high-range water-reducing and rheology-modifying agent designed to disperse fine particles, lower yield stress and control bleeding at high solids contents in sulfide rich tailings. Key-tested parameters included: • Solids content in the range 74–78 %; • Binder content 3 and 4 % of tailings cake weight; • Admixture dosages around 1.5-3 liters/m3. Lab prepared mix materials quantities detailed in Table 2 were calculated according ASTM D6023. Pumpability was assessed using mini-slump tests (modified smaller Abrams cone) and yield stress measurements using a Viscotester IQ rheometer (Figure 4 and 6). Unconfined compressive strength was measured on standard cylinders at 7, 14, 21, 28, 60 and 90 days of curing, following ASTM D4832 procedure (Figure 5). The main performance indicators were: • Ability to maintain or improve CPB pumpability at higher solids content; • Ability to maintain or improve UCS at different testing ages; • Potential reductions in binder and water for a given strength.
RkJQdWJsaXNoZXIy MTM0Mzk2