Over the past decades, cemented paste backfill (CPB) has become a common, environmentally friendly method of managing mine wastes (such as tailings). This technology allows up to 60% of the total amount of tailings to be reused and filled in the mine stopes after converting them into cemented material. Beside reducing the environmental risks associated with the traditional disposal of these materials, turning them into cemented material and placing them in the underground mine stopes can also provide secondary support for these stopes in addition to minimizing the risk of ground subsidence in the mine area. CPB is an engineered mixture of tailings, water, and hydraulic binder (such as cement, blast furnace slag, and fly ash) that is mixed in the paste plant and delivered into the mine stopes through a gravity or pumping based transportation system. During the transportation of CPB through the delivery system pipelines, the flowability of CPB depends on the rheology of the transported CPB, which is affected by different factors, such as the transportation time, temperature variation, binder type, and chemical composition of these mixtures. In addition, the performance of CPB, after placing the CPB mixture into the mine stopes, is mainly dependent on the role of the hydraulic binder, as it increases the mechanical strength of the mixture through the process of cement hydration. The mechanical strength is also influenced by different factors, such as time progress, temperature variation, and presence of chemical additives. It has previously been found that fresh CPB transported and/or placed in the mine stopes can be susceptible to temperature variation of different sources, such as the climatic effects, heat generated from the surrounding rocks, and heat generated during the process of cement hydration. Unsuitable flowability of CPB through the delivery system might lead to significant financial losses due to clogging of pipelines with unexpected hardening of CPB during transportation, which will cause delay in work and possible damages to the pipelines. Also, failure of CPB structure in the mine stopes due to inappropriate mechanical strength may cause casualties to the mine workers as well as significant environmental and economic damages. Many researchers studied the rheological properties and/or strength development of CPB under the individual effect of any of the aforementioned factors. Additionally, many researchers have evaluated the coupled effect of some of these factors on the rheology and mechanical strength of CPB material. Hitherto, there are currently no studies that addressed the combined effect of all these conditions on the rheological properties and strength development of CPB. At the first stage of this M.A.Sc. study, a series of experimental tests was conducted on fresh CPB in order to determine the combined effect of time, temperature, binder content, and chemical additives on the rheological properties of CPB. These experiments include rheological properties test (yield stress and viscosity), microstructural analysis (thermal analysis and XRD), chemical analysis (pH and Zeta potential), and monitoring tests (electrical conductivity), which were conducted on 125 CPB samples that were mixed and prepared at different temperatures (2oC, 20oC, 35oC) and cured for different curing time (0 hrs., 0.25 hrs., 1 hr., 2hrs, and 4 hrs.). These samples were prepared with different blends of hydraulic binders (PCI, PCI/Slag, and PCI/FA) and contained different dosages of sodium silicate (0%, 0.1%, 0.3%, and 0.5%). The results obtained show that rheology of CPB increases with the progress of curing time. It also increases with the increase in the initial (mixing and curing) temperature and content of sodium silicate. It was also found that the partial usage of slag and FA reduces the rheological properties. However, CPBs containing PCI/FA as binder have lower rheological properties, and thus better flowability, than those that contain PCI/Slag as binder. At the second stage of this M.A.Sc. study, in order to understand the combined effect of time, temperature and sodium silicate content on the strength development of slag-CPB, unconfined compression (UCS) test, microstructural analysis (thermal analysis and MIP), and monitoring tests (electrical conductivity, suction, and volumetric water content) were conducted on 72 CPB samples that were prepared with PCI-Slag as a binder, cured for different times (1 day, 3 days, 7 days, and 28 days) under different curing temperatures of (2oC, 20oC, 35oC), and contained different dosages of sodium silicate (0%, 0.3% and 0.5%). The results obtained at this stage showed that the strength development of slag-CPB increases with the progress of curing time and temperature. It also increases with the increase in the sodium silicate content. Also, the combined effect of high temperature, high dosage of sodium silicate and longer curing time showed significant enhancement in the mechanical strength of slag-CPB. The findings of this M.A.Sc. research will contribute to cost effective, efficient, and safer design of CPB structures in the mine areas. It will also help in minimizing financial loss associated with unsuitable flowability of CPB transported in the CPB delivery system besides reducing the risks of human loss, and the environmental and economic damages associated with the failure of CPB structures.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/41985 |
| Date | 12 April 2021 |
| Creators | Ali, Ghada Abdulbaqi |
| Contributors | Fall, Mamadou |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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