Flowability And Mechanical Properties Of Cemented Paste Backfill In Sub-zero Environments

The gradual depletion of ores available at shallow depths in a number of underground mines in various parts of the world(e.g., Canada, China) means that underground mines are increasingly being carried out in permafrost or cold regions which are characterized by sub-zero mining environments. Over the past thirty years, significant progress has been made by previous studies in understanding the flowability and mechanical stability of cemented paste backfill(CPB). However, most of previous studies are conducted at medium or high temperatures, no study has been performed on characteristic behaviour of CPB in the aforementioned sub-zero environments.This thesis aims to explore the flowability, mechanical properties and freezing behavior of CPB in sub-zero environments via a series of testing methods. The main innovative results are as follows:(1) The effect of main influencing factors(such as water-cement ratio, binder type and content, tailings type and sub-zero environmental temperatures) on yield stress, strength and deformation was first investigated. The mechanisms underlying the effect of different influencing factors on the aformentiaoned properties were revealed via mercury intrusion porosimetry(MIP), thermal analysis(TG/DTG), Zeta potential testing, electrical conductivity monitoring as well as p H test. The findings of this study have significant implications for the composion mixture design of CPB in permafrost and cold regions.(2) High columns equipped with ECH2O-5TE capacitance sensors and LVDT are developed to study the freezing behaviour(including physico-mechanical properties, temperature evolution, saturated hydraulic conductivity, volumetric water content and vertical deformation) of CPB. The effect of filling strategy and evaporation on the geotechnical properties of CPB is investigated. The evolution of the coupled thermal-hydro-mechanical-chemical(THMC) properties is also discussed. Besides, the scale effect on the properties of CPB is studied througha comparison between samples from the column and small samples(mould samples).(3) The time-dependent evolution of the yield stress, strength and deformation behaviour of CPB with different saline(Na Cl) concentrations in a sub-zero environment is studied. The effect of Na Cl on the flowability and mechanical properties of CPB in a sub-zero environment is assessed by studying the phase compositions of the binder hydration products and the microstructural evolution of the CPB specimens. The featured deformation of frozen CPB with various Na Cl concentrations in uniaxial compression test and the corresponding mechanisms are proposed. Mathematic relations between salinity and yield stress, strength as well as initial elastic modulus of CPB are also presented.