Measurement of the strength development of Cemented Paste Backfill in laboratory cast cylinders does not replicate the in situ strengths of CPB in mine stopes. The mass of CPB in a filled stope is large and temperature rises due to the heat of hydration of the cementing materials, thus accelerating the gain in strength, relative to laboratory specimens stored at ambient temperature. The purpose of this study was to determine the impact on strength development when CPB test cylinders were subjected to a temperature profile mimicking that in a large mass, such as a mine stope. Also, maturity (the integral of time and temperature during hydration of the CPB) was compared to actual strengths, and the maturity – strength concept used in concrete technology was applied. It was found that the strength- maturity relationship was applicable to CPB once the base line or datum temperature was adjusted.

Mining has been one of the main industries in the course of the development of human civilization and economies of various nations. However, every industry has issues, and one of the problems the mining industry has faced is the management of waste, especially sulphide-bearing tailings, which are considered to be a global environmental problem. This issue puts pressure on the mining industry to seek alternative approaches for tailings management. Among the several different types of methods used, cemented paste backfilling is one of the technologies that offers good management practices for the disposal of tailings in underground mines worldwide. Cemented paste backfill (CPB) is a cementitious composite made from a mixture of mine tailings, water and binder. This technology offers several advantages, such as improving the production and safety conditions of underground mines. Among these advantages, CPB is a promising solution for the management of sulphidic tailings, which are considered to be reactive materials (i.e., not chemically stable in an atmospheric condition) and the main source of acid mine drainage, which constitutes a serious environmental challenge faced by mining companies worldwide. Such tailings, if they come into direct contact with atmospheric elements (mainly oxygen and water), face oxidation of their sulphidic minerals, thus causing the release of acidic drainage (i.e., acid mine drainage) and several types of heavy metals into surrounding water bodies and land. Therefore, the reactivity of sulphidic tailings with and without cement content can be considered as a key indicator of the environmental behavior and durability performance of CPB systems. For a better understanding of the reactivity, it is important to investigate the influencing factors. In this research, several influencing factors are experimentally studied by conducting oxygen consumption tests on different sulphidic CPB mixtures as well as their tailings under different operational and environmental conditions. These factors include time, curing temperature, initial sulphate content, curing stress, mechanical damage, binder type and content, and the addition of mineral admixtures. In addition, several microstructural techniques (e.g., x-ray diffraction and scanning electron microscopy) are applied in order to understand the changes in the CPB matrices and identify newly formed products. The results reveal that the reactivity of CPB is affected by several factors (e.g., curing time, initial sulphate content, ageing, curing and atmospheric temperature, binder type and content, vertical curing stress, filling strategy, hydration and drainage, etc.), either alone or in combination. These factors can affect reactivity either positively or negatively. It is observed that CPB reactivity decreases with increasing curing time, temperature (i.e., curing and atmospheric temperatures), curing stress, binder content, the addition of mineral admixtures, degree of saturation, and the binder hydration process, whereas reactivity increases with increases in sulphide minerals (e.g., pyrite), initial sulphate content, mechanical damage, and with decreased degrees of saturation and binder content. The effect of sulphate on the reactivity of CPB is based on the initial sulphate content as well as curing time and temperature. It is concluded that the reactivity of CPB systems is time- and temperature-dependent with respect to other factors. Also, binders play a significant role in lowering CPB reactivity due to their respective hydration processes.

Finite element analysis was performed on an implanted femur, using loads of daily living activities, performed by total hip replacement patients. A probabilistic bone fatigue failure model was utilized to analysis the risk of post-operative femoral fracture in different patient groups, depending on bone fatigue strength for young and elderly patients, and activity levels for normal and active patients. Different bone-implant interface conditions were considered: after surgery, osseointegrated, fibrous tissue covering, and loose. For young patients, the probability of failure is less than 4% for all cases. While in elderly patients, high of 28.2% and 57.9% are reported for normal and active groups respectively. For both age groups and activity levels, loose stems had the highest probability of failure, while osseointegrated had the lowest.

Steel turning inserts cemented carbides have a binder phase consisting of cobalt (Co). However, in recent years a study from the United States National Toxicity Program (NTP) found that cobalt powder is carcinogenic upon inhalation. The European Union's REACH have therefore also classified cobalt powder as carcinogenic upon inhalation. The worldwide search to find a replacement has therefore lately intensified. It is important that the alternative binder phase has no negative effects on the properties of the insert. In this thesis the adhesion between a multilayer ceramic chemical vapor deposition (CVD) coating and a cemented carbide with the alternative binder phases consisting of iron (Fe), nickel (Ni) and cobalt (Co) has been studied. First of all, the fracture surfaces showed that the CVD coating was able to grow on all cemented carbides, regardless of which binder phase. To evaluate the adhesion, scratch tests were performed on all samples. The results from the scratch tests were not as expected. No chipping of the coating down to the cemented carbide occurred on any of the samples and the samples with the hardest cemented carbide did not get the highest critical load, which it should according to the literature if all other parameters were the same. Instead the sample with the binder phase consisting of 73 wt% iron and 27 wt% nickel had the highest critical load. This is thought to be due to that during the scratch test the binder phase in this cemented carbide would most likely transform into deformation martensite.

In this dissertation, a research effort aimed at development and implementation of a direct field test method to evaluate the linear and nonlinear shear modulus of soil is presented. The field method utilizes a surface footing that is dynamically loaded horizontally. The test procedure involves applying static and dynamic loads to the surface footing and measuring the soil response beneath the loaded area using embedded geophones. A wide range in dynamic loads under a constant static load permits measurements of linear and nonlinear shear wave propagation from which shear moduli and associated shearing strains are evaluated. Shear wave velocities in the linear and nonlinear strain ranges are calculated from time delays in waveforms monitored by geophone pairs. Shear moduli are then obtained using the shear wave velocities and the mass density of a soil. Shear strains are determined using particle displacements calculated from particle velocities measured at the geophones by assuming a linear variation between geophone pairs. The field test method was validated by conducting an initial field experiment at sandy site in Austin, Texas. Then, field experiments were performed on cemented alluvium, a complex, hard-to-sample material. Three separate locations at Yucca Mountain, Nevada were tested. The tests successfully measured: (1) the effect of confining pressure on shear and compression moduli in the linear strain range and (2) the effect of strain on shear moduli at various states of stress in the field. The field measurements were first compared with empirical relationships for uncemented gravel. This comparison showed that the alluvium was clearly cemented. The field measurements were then compared to other independent measurements including laboratory resonant column tests and field seismic tests using the spectral-analysis-of-surface-waves method. The results from the field tests were generally in good agreement with the other independent test results, indicating that the proposed method has the ability to directly evaluate complex material like cemented alluvium in the field. / text

The magnetic properties, coercivity, Hc, and weight-specific magnetic saturation, CoM, are two important quality characteristics in cemented carbides and ceramic metals, cermets. These properties give information about grain size and binder phase content, and are influenced by the different stages in the sintering process. This master thesis aim to investigate how the magnetic properties in cemented carbides are influenced by the top temperature during sintering and how the sintering processes used for cermets can be optimized in order to gain better magnetic properties in the final products. During the first part of the project, the temperature range investigated was 1380°C–1520°C. The results indicate that Hc in cemented carbides has a strong temperature dependence, where increasing top temperature results in lower Hc. In order to have approval limits for the furnace control pieces that follow the process directives, the limits used today need to become narrower. Furthermore, the results show that CoM also has a temperature dependence, although not as strongly as Hc. During the second part of the project, already existing data of the magnetic properties in four different cermet grades were evaluated. The results indicate that the two sintering processes used in the DDK furnace are generating too high results in Hc and CoM. Optimization tests were conducted and changes implemented in order to gain better results, where the DJ1430 process now has an increased time during the solid state sintering and the DF1480 process now has an increased time during the liquid phase sintering.

Pressing of metallic powders is a manufacturing process widely investigated in the research field and in the industry. This thesis project is focused on optimizing the pressing process of cemented carbide powder utilized for the production of triangular shaped cutting tool inserts. In particular, the filling of powder into the die cavity was investigated with respect to different pressing parameters. The aim of the project was to obtain a uniform density distribution of the powder into the die cavity, and hence to reduce the variation of the height of the insert obtaining more precise dimension of the latter. The tests were carried out at the Sandvik Coromant production department which is the creator of the project. The optimization of the pressing process was performed according to the Design of experiments theory. The dynamic of the sintering process was also investigated. The results showed a significant improvement in the filling of the die cavity and a significant decrease of the variation of the height of the inserts. The new insert obtained has more precise dimensions and is able to meet the more demanding requirements of the customers. The results achieved are directly applicable to a larger number of products, and indicate the direction to follow for further development of the manufacturing process.

Underground mining is a mineral acquisition technique that is critical to global economies, and human technological advancements. As shallow resource reserves are depleted, mine depths are increasing to accommodate global mineral demand. Increases in mine throughputs and excavation depths pose increased environmental concerns. Tailings surface disposal, and underground mine support are two considerable environmental and geotechnical factors of concern in current day mining. Underground waste disposal has been adopted by the mining industry in many forms. Cemented paste backfill (CPB) is a common best management practice developed to tackle these two specific resource industry related issues worldwide. CPB is a cement-stabilized material composed of tailings, water, and hydraulic binder. Tailings disposal areas on the earth’s surface are reduced by disposing of tailings in subsurface stopes that have been previously excavated. This increases underground safety by providing structural support to the mine. There are also economic benefits to this practice, as the additional support allows for adjacent pillars to be excavated. Although CPB greatly reduces tailings exposure to atmospheric elements, there are still underground environmental factors that must be considered with respect to environmental performance. CPBs are porous media, meaning they are susceptible to leaching of naturally occurring metals that are no longer in a stable condition as they were when incorporated in the parent rock. Arsenic and lead are metals of concern due to their association with many ore bodies. Leaching of these unstable metals may be influenced by the backfill curing temperature and the chosen hydraulic binder. Curing temperatures may be influenced by geographic location, local stope geology and depth, hydration and transport, among others. Hydraulic binders are chosen based on availability, cost, and desired mechanical properties of the paste. In this research, the effect of curing temperature and binder composition on the leachability of CPB are studied. ASTM C 1308 leaching protocol is used to determine the leachability of six CPBs. In addition, microstructural techniques (Powder X-Ray Diffraction, Mercury Intrusion Porosimetry, and Scanning Electron Microscopy) are used to relate the microstructural properties of the CPB to the leaching characteristics. Results reveal that CPBs cured with ordinary Portland cement (OPC) leach significantly less than CPBs cured with an OPC/Blast furnace slag (Slag) binder (50% blending ratio) as a result of CH consumption in slag hydration. Both CH and C-S-H are responsible for immobilizing arsenic in cement stabilized materials. OPC-CPBs contain greater relative quantities of CH, which aids in arsenic immobilization. Between the range of 2°C and 35°C OPC-CPB performed better at lower curing temperatures. Lower curing temperatures are favoured in OPC-CPB because the pore surface greater than the threshold pore diameter is reduced. Alternatively, OPC/Slag-CPB exhibited a decrease in cumulative mass leached at higher curing temperatures. The difference in cumulative mass leached by the OPC/Slag-CPBs is also related to the pore surface, and threshold pore diameter.

Doctor of Philosophy / Suction caissons have been used in the offshore industry in the last two decades as both temporary mooring anchorages and permanent foundation systems. Although there have been more than 500 suction caissons installed in various locations around the world,understanding of this concept is still limited. This thesis investigates the installation aspect of suction caissons, focusing on the installation in dense sand and layered soils, where sand is inter-bedded by silt and weakly cemented layers. The research was mainly experimental, at both normal gravity and elevated acceleration levels in a geotechnical centrifuge, with some numerical simulations to complement the experimental observations. This study firstly explored the suction caisson installation response in the laboratory at 1g. The influence and effect of different design parameters, which include caisson size and wall thickness, and operational parameters including pumping rate and the use of surcharge were investigated in dense silica sand. The sand heave inside the caisson formed during these installations was also recorded and compared between tests. The 1g study also investigated the possibility of installing suction caissons in layered sand-silt soil, where caissons were installed by both slow and rapid pumping. The heave formation in this case is also discussed. The mechanism of heave formation in dense sand and deformation of the silt layer was further investigated using a half-caisson model and the particle image velocimetry (PIV) technique. The installation response at prototype soil stress conditions was then investigated in a geotechnical centrifuge. The effects of caisson size, wall thickness, as well as surcharge were investigated in various types of sand, including silica sand, calcareous sand dredged from the North Rankin site in the North West Shelf (Australia), and mixed soil where silica sand was mixed with different contents of silica flour. Comparison with the 1g results was also made. The general trend for the suction pressure during installation in homogenous sand was identified. The installation in layered soil was also investigated in the centrifuge. The installation tests were performed in various sand-silt profiles, where the silt layers were on the surface and embedded within the sand. Comparison with the results in homogenous sand was made to explore the influence of the silt layer. Installations in calcareous sand with cemented layers were also conducted. The penetration mechanism through the cemented layer is discussed, and also compared with the penetration mechanism through the silt layer. Finite element modelling was performed to simulate key installation behaviour. In particular, it was applied to simulate the sand deformation observed in the PIV tests. The likely loosening range of the internal sand plug during suction installation in silica sand was estimated. By investigating the development of hydraulic gradient along the inner wall, the principle underlying the suction response for different combinations of selfweight and wall thickness was identified. FE modelling was also performed to explore the influence of the hydraulic blockage by the silt layer. This study found that the caissons could penetrate into all soils by suction installation. Among the key findings are the observations that the suction pressure increases with depth following a distinct pressure slope, corresponding to a critical hydraulic condition along the inner wall; and the installation was possible in both layered sand-silt and uncemented-cemented soils if sufficient pumping was available. While the caisson could penetrate the weakly cemented layers well with no notable adverse effects, problems were observed in the installation in layered sand-silt soil. These include piping failure in slow pumping rate installation at 1g, and the formation of extremely unstable soil heave during installation.

Cemented carbides based on tungsten carbide and cobalt arecommonly produced by a powder metallurgy route including liquidphase sintering. The pressed compact densifies to almost halfits volume during sintering due to pore elimination. Thesintering behaviour changes with material composition, such ascarbide grain size, binder fraction, carbon content andaddition of cubic carbides. This thesis is devoted to the study of constitutivebehaviour, in particular densification, and the microstructuralevolution during cemented carbide sintering. Dimensionalchanges are monitored using dilatometry with and withoutapplied external load. The microstructural evolution isinvestigated with light optical microscopy and scanningelectron microscopy. Thermodynamic calculations are used asreference. Constitutive relations are derived for uniaxial viscosity,viscous equivalent of Poisson’s ratio and sintering stressbased on relative density and temperature. The relations areextended to a model describing sintering shrinkage withexplicit dependencies on carbide grain size and binder content.The model is divided in three stages of which two pertain tothe solid state and the third to liquid phase sintering. Solidstate shrinkage is suppressed in a material with coarsecarbides and in the stage of liquid phase sintering grain sizestrongly influences the uniaxial viscosity. The binder contentaffects primarily the later densification. The effects of carbon content and grain size distribution onshrinkage have been studied. High carbon content enhancesshrinkage rate, but the effect of grain size distribution israther small. The mean carbide grain size is insufficient todescribe densification for very broad distributions only. Shrinkage occurs through rearrangement andsolution-reprecipitation. Rearrangement is studied through theevolution of the pore size distribution and simulatedgenerically using a discrete element method. Keywords:Cemented carbides, Sintering, Constitutiverelations, Microstructure, Densification, Modelling