Microstructural and Chemical Investigations of Cemented Paste Backfills
by T. Ramlochan, M.W. Grabinsky, and D.H. Hooton
Tailings and Mine Waste '04
Fort Collins, Colorado, 10-13 October 2004
This paper reports findings of microstructural and chemical investigations of four cemented paste backfill mixtures. The mictures were prepared from tailings, process water, and binders obtained from three participating mines. Scanning electron microscopy of polished sections revealed that the microstructures of the paste balcfils were largely void space that was highly connected. The hydration products did not effectively fill the interstitial space separating the tailings particles to form a cement matrix. This was attributed to hte high water contents used in the mixtures. The relative volume of interstitial space occupied by hydration products was greater when a binder consisting of blast-furnace slag and a small amount of Portland cement was used than when one with equal parts of Portland cement and fly ash was used. As a result, higher strengths were attained with the former than the latter at comparable water-to-cementitious-material ratios.
Self-desiccation of Cemented Paste Backfill and Implications for Mine Design
by M.W. Grabinsky and P. Simms
9th International Seminar on Paste and Thickened Tailings
Limerick, Ireland, 3-7 April 2006
The hydraulic and mechanical properties of Cemented Paste Backfill (CPB) that are of principle interest in Geomechanical Mine Design include rheology (both “closed conduit” and “open channel” flow), suction (the Soil Water Characteristic Curve or Water Retention Curve), permeability, stiffness, and static and dynamic strength (including resistance to liquefaction). All of these properties change as the binder in the CPB hydrates. In some, and perhaps most mining applications the rate of hydration, and therefore the rate of hydraulic and mechanical property change, occurs on a time scale comparable to the rate of CPB delivery to and filling of the stope. This means that the CPB’s properties are evolving even as it is being deposited and overprinted. This fact can have serious implications for how we interpret total stress cell results, how arching develops both within the stope and across the fill barricades, how fill barricades are designed and constructed, and how we evaluate the CPB’s ability to carry its own self-weight during filling (i.e., resistance to static liquefaction during filling) and subsequent mining (i.e., resistance to dynamic liquefaction during blasting in proximity to recent fills). This paper begins by considering some initially unexpected results from an in situ investigation that illustrates the interaction between rate of binder hydration and rate of stope filling. The framework for conducting tests to evaluate CPB’s evolving hydraulic and mechanical properties is then considered. Some initial test results involving static monotonic and cyclic loading of CPB are then reviewed, and the mine design implications of these test results are considered. The conclusions arising from this work are not yet meant to be used for practical design, but rather point to the extensive research and development that is still required before we can rationally carry out optimized design of CPB fills and their barricades.