Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii), a keystone species in western Washington, faces threats on plantations across this region from the invasive species Scotch broom (Cytisus scoparius (L.) Link), whose invasions on recently established stands can lead to mortality of Douglas-fir through overtopping. The susceptibility of sites to Scotch broom achieving dominance over Douglas-fir has been demonstrated as highly site dependent, however the site conditions that cause this have not yet been identified. Scotch broom has a demonstrated average maximum height of 3m, thus, after Douglas-fir exceeds this height, its risk of being overtopped is significantly reduced. This thesis strives to identify sites that were at the greatest risk Douglas-fir being overtopped by Scotch broom by first, identifying what factors improved growth of Douglas-fir during the period when they are at the greatest risk, and second, identifying factors that led to Douglas-fir outcompeting Scotch broom on sites they cohabitated. In Chapter 1, we utilized LiDAR scans, Soil Survey Geographic Database characteristics, and management histories to identify conditions that improved growth for Douglas-fir in ages 3-8. Individual tree detection was used to measure Douglas-fir heights, and a correction algorithm for LiDAR measured young Douglas-fir heights was established from field validation data. We identified that young Douglas-fir had improved growth on sites with lower elevation, flatter slopes, and finer textured soils. The factors identified were then transformed into four potential site index models based on mean stand elevation class, Mean stand elevation class and clay class, textural class and slope class, and textural class and Mean stand elevation class. In Chapter 2, we used paired field plots to examine Douglas-fir and Scotch broom competition on 19 sites across western Washington. Each site had 2 plots with only Douglas-fir and 2 plots with Douglas-fir and Scotch broom. Elevation, soil texture, and soil nutrient composition for carbon, nitrogen and available phosphorous were examined for influence on height and growth rate of both species. We identified that Scotch broom presence was negatively related to Douglas-fir height growth and that sites with either higher percentages of silt, lower concentrations of phosphorous, or higher percentages of Carbon were more likely to have growth patterns close to or exceeding Scotch broom. / Master of Science / Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) is a valuable timber species across western Washington that is commonly grown in plantations. In western Washington when Douglas-fir are planted on a site they often face competition from the invasive shrub Scotch broom (Cytisus scoparius (L.) Link). When Scotch broom invasions occur on a recently planted Douglas-fir stands, they can cause death of the trees if Scotch broom plants grow taller than the young Douglas-fir and obstruct their access to light, a process called overtopping. The risk of Douglas-fir being overtopped has been shown to be dependent on location, however what causes a location to be at risk of overtopping is yet unknown. Scotch broom has a demonstrated average maximum height of 3m, thus, after Douglas-fir exceeds this height, its risk of being overtopped is significantly reduced. This study aims to identify sites that were at the greatest risk Douglas-fir being overtopped by Scotch broom by first, identifying what sites generate the best Douglas-fir growth when they are young and at risk of being overtopped, and second, identifying site characteristics led to Scotch broom growing faster than Douglas-fir on sites they both occur on. To identify sites that produced greater young Douglas-fir height growth we used publicly available soil data from the Soil Survey Geographic Database and company management histories to predict tree heights measured through aerial laser scanning (LiDAR). We found that sites with soil textures that had higher percentages of smaller particles, were on lower elevations, and had gentler hillslopes could all produce greater Douglas-fir height growth. When attempting to identify what causes Douglas-fir to be at risk of being overtopped by Scotch broom we used plots with and without Scotch broom on a variety of field sites. This allowed us to not only identify which characteristics of sites where Douglas-fir was being outgrown by Scotch broom, but also identify if Scotch broom was changing how Douglas-fir grew. We found that reductions in Douglas-fir growth were related to Scotch broom being present and that increases in soil silt percentages, decreases in soil phosphorus concentrations, and increases in soil carbon percentages were related to Douglas-fir having height growth closer to or exceeding that of scotch broom.

Advanced drug delivery systems have shown immense success through nanotechnology which overcomes the challenges posed by large sized particles such as poor solubility, bioavailability, absorption, and target-specific delivery. This study focuses on nano sizing by application of microreactor technology and nanoparticles to obtain polymeric particulate with a selection of model drugs for inhalation drug delivery routes. The development of nanoparticles of two challenging compounds in terms of solubility and permeability, namely Ibuprofen (IBU) and Salmeterol (SAL), was conducted using a continuous, controlled, and scalable system offered by microfluidic reactor with the incorporation of anti-solvent approach. The research explores the potential of this technology to enhance absorption rate and hence bioavailability of IBU via oral route, and SAL via inhalation. IBU, an anti-inflammatory drug, is classified as BCS Class II drug with low solubility and high permeability. SAL is a selective long acting β2-agonist which is co-dispensed along with a short-acting β2-agonist for quick relief of acute bronchoconstriction due to its long onset of action. This lack of the ‘kick’ effect in SAL can be attributed to its relatively higher lipophilicity which causes a delay in the diffusion to the β2 receptors on the smooth muscles. It is therefore feasible to assume that increasing the dissolution and/or diffusion rate of SAL in the interstitial fluids would reduce the delay between administration and the onset of action of this drug which would be beneficial to patients. Process and formulation parameters were investigated to optimize the production and stability of nano particles of both drugs using Y shaped microfluidic reactors. IBU results show that the smaller the angle between the two inlets were the smaller the particle size achieved. Moreover, the particle size increased with increasing the concentration of IBU solution. The effect of the polymer mixture ratio (PVP/HPMC) on the initial particle size was not clear though. The smallest particle size (113 nm) was achieved using 10° Y shaped chip with IBU concentration of 1 mg/mL and a polymer mixture of 0.3% w/v PVP and 0.5% w/v HPMC. Using a polymer mixture of 0.5% w/v of each polymer though yielded a better PDI (140nm and PDI of 0.5). Same observations were noted when the syringe pumps were replaced with a non-pulsatile pressure pump. Particle size though dropped significantly to 33nm. Stability data showed that all systems were practically stable regardless of the process or formulation parameters. In addition, a considerable 2.5 fold increase in dissolution rate was observed in the first 20 minutes when compared to the raw material. The optimized parameters were applied to SAL to produce nanocrystals with best result (59 nm) were obtained using 50µg/mL Salmeterol with microfluidics inlet angle 10° with non-pulse syringe pump. The stabilizing mixture was PVP 0.8% w/v and Tween 80 at a concentration of 0.02%. This approach offered a basis for the generation of nano sized SAL particles with higher fine particle fraction and better deposition in NGI than currently marketed formulations, thus providing a more efficient drug dose delivery and lung deposition.

No description available.

Yes / The tribological performance of the piston assembly of an automotive engine is highly influenced by the complex flow mechanisms that supply lubricant to the upper piston rings. As well as affecting friction and wear, the oil consumption and emissions of the engine are strongly influenced by these mechanisms. There is a significant body of work that seeks to model these flows effectively. However, these models are not able to fully describe the flow of lubricant through the piston assembly. Some experimental studies indicate that droplets of lubricant carried in the gas flows through the piston assembly may account for some of this. This work describes an investigation into the nature of lubricant misting in a fired gasoline engine. Previous work in a laboratory simulator showed that the tendency of a lubricant to form mist is dependent on the viscosity of the lubricant and the type and concentration of viscosity modifier. The higher surface area-to-volume ratio of the lubricant if more droplets are formed or if the droplets are smaller is hypothesised to increase the degradation rate of the lubricant. The key work in the investigation was to measure the size distribution of the droplets in the crankcase of a fired gasoline engine. Droplets were extracted from the crankcase and passed through a laser diffraction particle sizer. Three characteristic droplet size ranges were observed: Spray sized (250–1000 μm); Major mist (30–250 μm); and Minor mist (0.1–30 μm). Higher base oil viscosity tended to reduce the proportion of mist-sized droplets. The viscoelasticity contributed by a polymeric viscosity modifier reduced the proportion of mist droplets, especially at high load.

Bottom ash (BA), generated from the incineration of municipal solid waste (MSW), contains valuable elements which present a potential economic incentive to attempt recovery. The first study of this thesis investigated the physical, chemical, and mineralogical characterization of MSWI-BA samples through a number of experiments. To develop a proper physical characterization of the BA material, the sample was ground and subjected to particle size distribution, wet magnetic separation, and a float-sink test. As for the chemical and mineralogical characterization, the sample was subjected to XRD, XRF, SEM-EDX, and elemental composition analysis. Additionally, sequential chemical extraction and acid-leaching tests were conducted. The results from this section revealed that carrying out a combination of beneficiation processes using the MSWI-BA sample previously classified into the coarse, middle, and fine-size fractions could lead to better metal concentration yield and recovery optimization. The wet magnetic separation showed outstanding metallurgy indicators towards Fe, with enrichment ratios close to 2.0 and recovery values near to 80%. Metals such as Cu and Co were also enriched by 1.51 and 1.66, respectively, suggesting that the magnetic separation performance and enrichment are a function of the bound of multi-metallic oxides fractions. The 2.95 SG density test reached enrichment ratios higher than 2.0 in Fe, Cu, Co, and Ni in the coarse fraction of the BA fraction, which decreases when reducing the size fraction. When reducing the density cutoff, the results showed that the sink fraction yield increased as the medium density decreased, and the enrichment ratios of the minor elements (Mn, Co, Ni, Sn, and V) were similar across the different size fractions. Complementary information was obtained by the mineralogical characterization of the enriched streams from the physical concentration test, which explains the results obtained. The Cu speciation and mineral phases identified were copper oxide, copper sulfate, and cupric sulfite. While the main Fe-rich constituents existed in chemical forms of iron oxides, such as magnetite, hematite with substituted varieties, spinel group, and metallic inclusions. The enrichment ratios of Mn, Cr, Cu, and Ni obtained through magnetic separation can be explained by the presence of metallic inclusions, where these elements exhibit an affinity for the iron-bearing particles. The acid leaching test revealed that metals such as Fe, Mn, Co, Cu, and Zn can be efficiently leached using 1M HCl within 30 min of the reaction. The second part of this research study constituted the evaluation of the effect of the particle size reduction, which was performed to assess the intraparticle heterogeneity of MSWI BA. The evaluation consisted of particle size reductions by crushing and grinding for different residence times and then subjecting the sample to a sequence of physical concentration tests, such as particle size distribution, froth flotation, and wet magnetic separation. Additionally, the elemental composition after each test was determined through ICP-MS analysis to compare the particle size effect in the recovery and concentration of the valuable elements. The elemental composition results revealed that the comminution process promotes the interaction of Fe, Zn, and Cu, in the fine fraction, by generating more surface area. In contrast, the minor elements were not significantly enriched by reducing the size fraction, suggesting that the comminution process does not impact the mobility and redistribution of the elements in low concentrations. The froth flotation performed in this study showed that when using 0.338 g/ton diesel as a collector, adjusting and controlling the pH between 8.8 to 9.2 throughout the test, the organic matter content can be efficiently reduced in the BA sample from 14.73% to 4.25% when the sample has been previously ground for 30 min. Slight enrichment ratios were observed in the concentrate stream of the froth flotation, suggesting that these elements are associated with the organic matter in the BA sample. In contrast, the wet magnetic separation results revealed significant enrichment ratios of Fe, Mn, Co, and Ni after 10 min of grinding. / Master of Science / The Bottom Ash (BA) generated by the incineration of household solid waste has been identified as a promising source of valuable elements. However, a comprehensive understanding of the BA sample's properties is required in order to determine the most suitable mineral processing method to enrich the elements. The first study of this research consisted of evaluating BA ash's physical, chemical, and mineralogical properties in the BA sample. Following the characterization study, the effect of particle size, as a function of the grinding time, in the valuable elements' enrichment was evaluated. The results suggest that Ti, Fe, Cu, and Zn are the major and most valuable elements, while Mn, Co, Ni, Sb, and V are valuable elements in a minor concentration in the BA samples. Some elements, such as Ti, Sc, Co, Mn, Ni, Sn, and V, have been declared by the US Department of the Interior as critical minerals due to their economic importance and vulnerability to supply chain disruption. Although Fe and Cu are not considered critical minerals, their consumption in 2022 was 40 and 1.9 million metric tons, respectively. The development of national industry and enhancing the understanding of the alternative sources for the valuable elements present an opportunity to diversify local suppliers, pursue a vertical integration of the economic model, and reduce the third-party international vendors' dependency. Likewise, this research supports the aims to reduce the demand for primary natural resources and contribute to the circular economy model, in which energy, resources, and material are kept in a lifecycle while reducing landfilling disposal.

No / PURPOSE: To explore the use of crystal inter-planar d-spacings and slip-plane interaction energies for predicting and characterising mechanical properties of crystalline solids. METHODS: Potential relationships were evaluated between mechanical properties and inter-planar d-spacing, inter-planar interaction energy, and dispersive surface energy as determined using inverse gas chromatography (IGC) for a set of pharmaceutical materials. Inter-planar interaction energies were determined by molecular modelling. RESULTS: General trends were observed between mechanical properties and the largest inter-planar d-spacing, inter-planar interaction energies, and IGC dispersive surface energy. A number of materials showed significant deviations from general trends. Weak correlations and outliers were rationalised. CONCLUSIONS: Results suggest that the highest d-spacing of a material could serve as a first-order indicator for ranking mechanical behaviour of pharmaceutical powders, but with some reservation. Inter-planar interaction energy normalised for surface area shows only a weak link with mechanical properties and does not appear to capture essential physics of deformation. A novel framework linking mechanical properties of crystals to the distinct quantities, slip-plane energy barrier and inter-planar interaction (detachment) energy is proposed.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Hydrocyclones are stationary separating machines that separate materials based on centrifugal separation and are widely used in chemical engineering and mineral processing industries. Their design and operation, compact structure, low running costs and versatility all contribute to their applications in liquid clarification, slurry thickening, solid washing and classification. With any of these operations, the overall profitability of the process relies on the effective control of the process equipment. However, in practice, hydrocyclones are difficult to monitor and control, owing to the complexity and difficulty in measuring internal flows in the equipment. Several studies have indicated that hydrocyclone underflow images can be used to monitor process conditions. The research described in this thesis considers the use of image analysis to monitor particle size and solids concentration in the underflow discharge of a hydrocyclone. The experimental work consisted of laboratory and industrial-based case studies. The laboratory cyclone used was a 76 mm general laboratory cyclone. A Canon EOS 400D digital camera was used for the underflow imaging. Image features such as pixel intensity values, underflow discharge width and grey level co-occurrence matrix (GLCM) were extracted from the images using MATLAB Toolbox software. Linear discriminant analysis (LDA) and neural network (NN) classification models were used to discriminate between different PGM ore types based on features extracted from the underflow of the hydrocyclone. Likewise, multiple linear regression and neural network models were used to estimate the underflow solids content and mean particle size in the hydrocyclone underflow. The LDA model could predict the PGM ore types with 61% reliability, while the NN model could do so with a statistically similar 62% reliability. The multiple linear regression models could explain 56% and 40% of variance in the mean particle size and solids content respectively. In contrast, the neural network model could explain 67% and 45% of the variance of the mean particle size and solids content respectively. For the industrial system, a 100% correct classification was achieved with all methods. However, these results are regarded as unreliable, owing to the insufficient data used in the models. / AFRIKAANSE OPSOMMING: Hidrosiklone is stasionêre skeidingsmasjiene wat materiale skei op grond van sentrifugale skeiding en word algemeen gebruik in die chemiese ingenieurswese en mineraalprosessering industrieë. Hul ontwerp en werking, kompakte struktuur, lae bedryfskoste en veelsydigheid dra by tot hul gebruik vir toepassings in vloeistofsuiwering, slykverdikking, vastestof wassing en klassifikasie. In enige van hierdie prosesse hang die oorhoofse winsgewendheid van die proses af van die effektiewe beheer van die prosestoerusting. In die praktyk is hidrosiklone egter moeilik om te monitor en beheer weens die kompleksiteit en moeilikheidsgraad daarvan om die interne vloei in die apparaat te meet. Verskeie studies het aangedui dat hidrosikloon ondervloeibeelde gebruik kan word om die proseskondisies te monitor. Die navorsing beskryf in hierdie tesis maak gebruik van beeldanalise moniteringstegnieke om die ertstipes en grootte- verspreidingsgebiede/ klasse van die ondervloei afvoerpartikels te bepaal. Sodoende word ‘n grondslag gelê vir verbeterde sikloon monitering en beheer. Die eksperimentele werk het bestaan uit beide laboratorium en industrieel-gebaseerde studies. Die laboratorium sikloon wat gebruik is, was ‘n 76 mm algemene laboratorium sikloon. ‘n Canon EOS 400D digitale kamera is gebruik om die hidrosikloon ondervloei beelde vas te vang. Beeldeienskappe soos beeldelement intensiteitswaardes, ondervloei afvoerwydte en grysvlak mede-voorkoms matriks is onttrek uit die beelde deur gebruik te maak van MATLAB Toolbox sagteware. Lineêre diskriminantanalise (LDA) en neural netwerk (NN) klassifikasiemodelle is gebou om te onderskei tussen die verskillende PGM ertse en gebaseer op veranderlikes wat afgelei is uit beelde van die ondervloei van die sikloon. Net so is daar ook gebruik gemaak van lineêre regressie- en neural netwerkmodelle om die vasestofkonsentrasie en gemiddelde partikelgrootte in die ondervloei van die sikloon te beraam. Die LDA model kon die PGM ertstipes met 61% betroubaarheid voorspel, terwyl die neural netwerkmodel dit kon doen met statisties dieselfde betroubaarheid van 62%. Die lineêre regressiemodelle kon onderskeidelik 56% en 40% van die variansie in die gemiddelde partikelgrootte en vastestofkonsentrasie verduidelik. In teenstelling iermee, kon die neurale netwerkmodel 67% en 45% van die variansie in die gemiddelde partikelgrootte en vastestofkonsentrasie verduidelik. In die nywerheidstelsel kon beide tipe modelle perfekte onderskeid tref tussen die partikelgroottes wat gemeet is op opeenvolgende dae van die bedryf van die siklone. Hierdie resultate is egter nie betroubaar nie, a.g.v. die beperkte hoeveelheid data wat beskikbaar was vir modellering.

Cette étude porte sur le broyage en voie humide (nanobroyage) de produits organiques à usage pharmaceutique dans un broyeur à billes agité. L'objectif des travaux réalisés était d'analyser la faisabilité de l'opération de nanobroyage et d'améliorer la compréhension des processus de réduction de taille dans le cas de produits organiques cristallins. Dans un premier temps, des expériences préliminaires ont été menées pour le choix d'agents mouillants et dispersants adéquats pour les matériaux choisis (ciclopirox, ibuprofène) et pour la mise au point du mode de fonctionnement du procédé de broyage. Nous avons également testé différentes techniques comme la spectroscopie acoustique et la diffusion dynamique de la lumière pour caractériser la distribution de taille des particules broyées, en se basant sur une étude expérimentale conduite sur la calcite, utilisée dans cette étude comme matériau de référence. La seconde partie a été consacrée au broyage par microbilles appliqué aux différents matériaux choisis. Nous avons étudié l'influence des paramètres opératoires tels que le débit de suspension, la vitesse de rotation de l'agitateur, la taille des billes de broyage et la concentration en solide sur l'efficacité énergétique du procédé et la qualité des produits broyés. Les critères de qualité pris en compte dans cette étude sont la distribution de taille des particules, la stabilité et le comportement rhéologique des suspensions broyées ainsi que les propriétés structurales du produit. L'effet du broyage sur les changements microstructuraux des différents produits a enfin été analysé. Une attention particulière a également été portée sur l'effet de la température sur le procédé de réduction de taille et les propriétés de l'ibuprofène broyé. / This work focuses on wet grinding (nanogrinding) of organic materials for pharmaceuticals using a stirred media mill. The aim of the work was to examine the feasibility of nanogrinding process and to improve the understanding of size reduction processes applied on crystalline organic products. Firstly, preliminary investigations were conducted to make a choice of appropriate wetting agents and dispersants for the selected materials (ciclopirox, ibuprofen), and for the development of the operation mode of the grinding process. We also tested different techniques such as acoustic attenuation spectroscopy and dynamic light scattering to characterize the ground particle size distribution, based on an experimental study conducted on calcite, used in this study as reference material. The second part was devoted to the milling process by grinding beads applied to the selected materials. The influence of operating parameters such as suspension flow rate, stirrer tip speed, grinding media diameter and solid mass concentration on grinding process efficiency and ground products quality were investigated. The quality criteria considered in this study are particle size distribution, stability and rheological behaviour of the products, as well as their structural properties. The effect of grinding process on the microstructural change of different materials was finally analysed. Particular attention was also focused on the effect of temperature on size reduction process and ground ibuprofen properties.

Résumé : Cette étude examine l'impact de la taille et de la gradation de particules sur les corrélations théoriques et empiriques existantes les plus connues entre la résistance au cisaillement et le comportement dilatatant des matériaux granulaires en condition de déformation plane et en compression triaxiale drainée. À cette fin, 276 tests de cisaillements symétriques directs et 35 tests de compressions triaxiales drainées ont été menés sur des échantillons composés de billes de basalte (particules rondes), et de sables constitués de particules angulaires (sable de Péribonka et sable d'Eastmain) sur une échelle de 63 µm à 2000 µm afin d'évaluer leur résistance au cisaillement et leur comportement de dilatance sur une vaste échelle de pressions normales et de densités relatives initiales. Premièrement, la fiabilité et l'applicabilité des limites de mesure à l’aide de tests physiques de cisaillements symétriques directs dans l'interprétation de la résistance au cisaillement frictionnel en déformation plane des matériaux granulaires ont été discutées et confirmées par l'usage du code informatique DEM, SiGran. L'accent a été particulièrement mis sur la validation du modèle DEM au moyen de comparaison des résultats des simulations DEM avec leurs équivalents physiques à une échelle macro. Les résultats virtuels DSA sont abordés du point de vue de la coaxialité entre les principales tensions et les principales directions des paliers de pression ainsi que de la déviation de la direction d'extension nulle à partir de la direction horizontale. Les résultats numériques fournissent également des données quantitatives sur les différentes formes d'énergie consommées durant le cisaillement confirmées par d'autres résultats physiques et numériques publiés. Sur la base des postulats précédents, un examen minutieux des résultats des essais de cisaillements directs et de données issues de la littérature a été accompli afin d'évaluer la fiabilité des formules empiriques bien connues de Bolton et Collins et al. avec leurs constantes couramment employées en condition de déformation plane. L'étude montre qu'une application des relations empiriques de force-dilatation de cisaillement avec les constantes proposées par Bolton (1986) et Collins et al. (1992) aux sables ayant une distribution de taille de particules différente peut conduire à surestimer leurs valeurs en terme de force de cisaillement. Dans cette étude, les coefficients des équations de Bolton et Collins et al. ont donc été ajustée afin de prendre en compte les caractéristiques des particules, en particulier le diamètre médian, D50. De manière analogue, les effets microstructuraux imposés par la géométrie interne des particules (par exemple la taille, la forme et la gradation des particules) sur la relation tension-dilatation très connue, celle de Rowe (1962), et son ajustement empirique en condition triaxiale drainée ont été examinés dans cette étude. Une comparaison des prédictions des formules proposées avec les données de force de cisaillement issues de la littérature fournit de nombreuses preuves en faveur des contraintes mises en place au sein des relations existantes de force-dilatation de cisaillement en condition de déformation plane et triaxiale. Ces comparaisons prouvent également que la prise en compte de la taille des grains conduit à des résultats plus tangibles que lorsque la taille de la particule n'est pas considérée. Les formules de force-dilatation ajustées peuvent se révéler avantageuses pour évaluer indépendamment la cohérence des forces de cisaillement déterminées expérimentalement et pour introduire des lois d’écoulement plus précises dans les analyses géotechniques analytiques et numériques. / Abstract : The present study examines more closely the potential impact of particle size and gradation on the most famous existing theoretical and empirical correlations between the shear strength and the dilation behavior of granular materials in plane strain and drained triaxial compression conditions. For this purpose, 276 symmetrical direct shear and 35 drained triaxial compression tests have been carried out on samples made up of basalt beads (rounded particles), and sands consisting of angular particles (Péribonka sand and Eastmain sand) in the range of 63 µm to 2000 µm to evaluate their shear resistance and dilation behavior over a wide range of normal pressures and initial relative densities. First, the reliability and applicability of boundary measurements in physical symmetrical direct shear tests to interpret the plane strain frictional shearing resistance of granular material have been discussed and confirmed using DEM computer code SiGran. Particular emphasis is placed on the validation of the DEM model by comparing the results of DEM simulations with their physical counterparts at the macro-scale. The virtual DSA results are discussed in terms of the coaxiality between the principal stresses and the principal strains increments directions as well as the deviation of the zero extension direction from the horizontal direction. The numerical results also provide quantitative data on different forms of energy consumed during shearing confirming other published physical and numerical results found in the literature. Following the assumptions above, a close scrutiny of symmetrical direct shear test results and strength and dilation data from the literature have been done to evaluate the reliability of well-known empirical Bolton’s and Collins et al.’s formulations with their commonly used constants in plane strain condition. The study shows that an application of empirical shear strength-dilation relationships with the constants proposed by Bolton (1986) and Collins et al. (1992) to sands with different particle-size distribution may strongly over-predict their shear strength values. In this study, the coefficients of Bolton’s and Collins et al.’s equations have been, therefore, adjusted to account for particle characteristics, in particular for D50. Similarly, the microstructural effects imposed by internal particle geometry (e.g. particle-size, particle shape, and particle gradation) on most popular stress-dilatancy relationship of Rowe (1962), and its empirical adjustment in drained triaxial condition have been investigated in this study. A comparison of the predictions by the proposed formulas with shear strength data from the literature provides evidences in support of the implemented constraints into existing shear strength-dilation relations in plane strain and drained triaxial conditions. These comparisons also proves that accounting for the grain size yields more authentic results than when particle size is not considered. The adjusted strength-dilation formulas may be beneficial for independently assessing the consistency of the experimentally-determined shear strengths, and introducing more refined flow rules into analytical and numerical geotechnical analyses.

Abstract : Although concrete is a relatively green material, the astronomical volume of concrete produced worldwide annually places the concrete construction sector among the noticeable contributors to the global warming. The most polluting constituent of concrete is cement due to its production process which releases, on average, 0.83 kg CO[subscript 2] per kg of cement. Self-consolidating concrete (SCC), a type of concrete that can fill in the formwork without external vibration, is a technology that can offer a solution to the sustainability issues of concrete industry. However, all of the workability requirements of SCC originate from a higher powder content (compared to conventional concrete) which can increase both the cost of construction and the environmental impact of SCC for some applications. Ecological SCC, Eco-SCC, is a recent development combing the advantages of SCC and a significantly lower powder content. The maximum powder content of this concrete, intended for building and commercial construction, is limited to 315 kg/m[superscript 3]. Nevertheless, designing Eco-SCC can be challenging since a delicate balance between different ingredients of this concrete is required to secure a satisfactory mixture. In this Ph.D. program, the principal objective is to develop a systematic design method to produce Eco-SCC. Since the particle lattice effect (PLE) is a key parameter to design stable Eco-SCC mixtures and is not well understood, in the first phase of this research, this phenomenon is studied. The focus in this phase is on the effect of particle-size distribution (PSD) on the PLE and stability of model mixtures as well as SCC. In the second phase, the design protocol is developed, and the properties of obtained Eco-SCC mixtures in both fresh and hardened states are evaluated. Since the assessment of robustness is crucial for successful production of concrete on large-scale, in the final phase of this work, the robustness of one the best-performing mixtures of Phase II is examined. It was found that increasing the volume fraction of a stable size-class results in an increase in the stability of that class, which in turn contributes to a higher PLE of the granular skeleton and better stability of the system. It was shown that a continuous PSD in which the volume fraction of each size class is larger than the consecutive coarser class can increase the PLE. Using such PSD was shown to allow for a substantial increase in the fluidity of SCC mixture without compromising the segregation resistance. An index to predict the segregation potential of a suspension of particles in a yield stress fluid was proposed. In the second phase of the dissertation, a five-step design method for Eco-SCC was established. The design protocol started with the determination of powder and water contents followed by the optimization of sand and coarse aggregate volume fractions according to an ideal PSD model (Funk and Dinger). The powder composition was optimized in the third step to minimize the water demand while securing adequate performance in the hardened state. The superplasticizer (SP) content of the mixtures was determined in next step. The last step dealt with the assessment of the global warming potential of the formulated Eco-SCC mixtures. The optimized Eco-SCC mixtures met all the requirements of self-consolidation in the fresh state. The 28-day compressive strength of such mixtures complied with the target range of 25 to 35 MPa. In addition, the mixtures showed sufficient performance in terms of drying shrinkage, electrical resistivity, and frost durability for the intended applications. The eco-performance of the developed mixtures was satisfactory as well. It was demonstrated in the last phase that the robustness of Eco-SCC is generally good with regards to water content variations and coarse aggregate characteristics alterations. Special attention must be paid to the dosage of SP during batching. / Résumé : Même si le béton est un matériau relativement vert, le volume astronomique de béton produit à travers le monde chaque année met le secteur de la construction en béton parmi les contributeurs important au réchauffement climatique. Le constituant le plus polluant du béton est le ciment en raison de son processus de production qui dégage, en moyenne, 0,83 kg de CO[indice inférieur 2] par kg de ciment. Le béton autoplaçant (BAP), un type de béton qui peut remplir le coffrage sans vibration externe, est une technologie qui peut offrir une solution aux problèmes de développement durable de l'industrie du béton. Cependant, toutes les exigences de la maniabilité du BAP proviennent d'une teneur en poudre plus élevé (par rapport au béton conventionnel), ce qui peut augmenter le coût de la construction et de l'impact environnemental du BAP pour certaines applications. Le BAP écologique, Éco-BAP, est un développement récent combinant les avantages du BAP tout en ayant une teneur en poudre significativement plus faible. La teneur en poudre maximale de ce béton, destinée à la construction du bâtiment et aux applications commerciales, est limitée à 315 kg/m[indice supérieur 3]. Néanmoins, la conception de l’Éco-BAP peut être difficile, car un équilibre délicat entre les différents ingrédients de ce béton est nécessaire pour garantir un mélange satisfaisant. Dans ce programme de doctorat, l'objectif principal est de développer une méthode systématique pour la formulation de l’Éco-BAP. Puisque l'effet de groupe des particules (EGP) est un paramètre clé pour la conception des mélanges l’Éco-BAP stables, et que ce phénomène est peu connu, dans la première phase de cette recherche, l’EGP est étudié. Cette partie se concentre sur l'influence de la granulométrie sur l’EGP et la stabilité des mélanges de modèle ainsi que des BAPs. Dans la deuxième phase, le protocole de formulation est développé, et les propriétés des mélanges obtenus, à l’état frais ainsi que l’état durcis, sont évaluées. Étant donné que l'évaluation de la robustesse est cruciale pour la production du béton à grande échelle, dans la dernière phase de ce travail, la robustesse d'un des mélanges les plus performants de la Phase II est examinée. Basé sur les résultats obtenus, nous constatons que l'augmentation de la fraction volumique d'une classe mène à une meilleure stabilité de cette classe. Cela contribue également à une EGP supérieure du squelette granulaire et à une stabilité plus élevée du système. Il a été montré qu'une granulométrie continue dans lequel la fraction volumique de chaque classe est plus grande que la classe consécutive plus grossière peut augmenter l’EGP. En utilisant une telle granulométrie, la fluidité d’un mélange du BAP pourrait être augmentée sans compromettre la résistance à la ségrégation. Un indice de prédiction du potentiel de la ségrégation de particules suspendues dans un fluide à seuil a été proposé. Dans la deuxième phase de la thèse, une méthode de conception en cinq étapes pour l’Éco-BAP a été développée. Le protocole de formulation commence par la détermination des teneurs en poudre et de l'eau, suivie par l'optimisation des fractions volumiques du sable et des gros granulats selon un modèle idéal de granulométrie (Funk et Dinger). La composition de poudre est optimisée dans la troisième étape afin de minimiser la demande en eau tout en garantissant une performance adéquate à l'état durci. Le dosage du superplastifiant (SP) est déterminé dans l’étape suivante. La dernière étape s’agit d’évaluer le potentiel du réchauffement climatique des mélanges développés. Les mélanges de l’Éco-BAP optimisés répondent à toutes les exigences à l'état frais pour le BAP. La résistance à la compression à 28 jours de ces mélanges est dans la fourchette cible de 25 à 35 MPa. En outre, les mélanges montrent des performances suffisantes en termes de retrait de séchage, la résistivité électrique, et la résistance contre gel-dégel pour les applications visées. La performance écologique des Éco-BAPs produis a été satisfaisante. Il a été démontré dans la dernière phase que la robustesse de l'Éco-BAP est généralement bonne en ce qui concerne les variations de teneur en eau et les changements de propriétés des gros granulats. Une attention particulière doit être accordée au dosage du SP pendant le malaxage.