Tesi sul tema "Clay"

Leda clay, which is a type of sensitive marine clay in Canada, is a hazardous soil that could undergo sudden collapse and flow upon wetting and remolding. This type of soil causes many landslide disasters and foundation damage. The existence of Leda clay at or near the proximities of developed cities makes it challenging for infrastructure expansion, and therefore, challenging for geotechnical engineers. At the location where this sensitive marine clay exists, many foundation designers have adopted the use of deep foundations, such as pile foundations to support heavy structures. The shear behavior and strength parameters at the interface between the (friction) pile and soil are key design parameters. A sufficient knowledge of these interface shear behaviors and strength parameters is also essential for the safe and cost-effective design of several other geotechnical structures (e.g., retaining walls, reinforced soils, and buried structures). However, no studies have yet been implemented on the interface shear behavior between Leda clay and structural material. There is therefore, a need to generate more knowledge about the interface shear behavior of Leda clay. This thesis deals with an experimental study of the shear behavior at the interface between Leda clay and structural material, such as steel and concrete. The effects of several factors, such as surface roughness of the construction material, Leda clay's overconsolidation ratio (OCR), saturation degree, density, and salt content on interface shear behavior are also investigated. Laboratory tests have been carried out by using an automatic direct shear machine connected to a linear variable differential transformer (LVDT), loading cell and a data logging system. The results of the interface shear tests show that under consolidated drained (CD) and saturated conditions, the interface friction angle increases with an increase in the clay's OCR. The results also indicate that increasing the salinity of Leda clay's pore water enhances its frictional resistance at the interface. Furthermore, the results reveal that Leda clay with a higher dry density shows higher interface shear resistance. On the other hand, the results also show that the interface shear resistance decreases as the degree of saturation of the Leda clay increases.

Three commercial clays: Cloisite Na+ , Cloisite 30B and Cloisite 15A were used to melt compound with a number of polymer matrices, including polypropylene (PP), poly(butylene terephthalate) (PBT) and polyamides (PA). X-ray diffraction (XRD), contact angle measurement and thermogravimetric analysis (TGA) showed small interlayer space, poor compatibility and low thermal stability of these nanocomposites, resulting in poor mechanical properties in composites. A number of modifications of commercial clays were carried out, including silylation and introduction of thermally stable surfactants, e.g. alkyl quaternary phosphonium cations and polyhedral oligomeric silsesquioxane (POSS). It was found that poor compatibility between polymer matrices and organically modified clays, especially in those POSS modified clays, again restricted the formation of exfoliated structure in polymer matrices. A mode of dual-surfactant modification for clay was developed, and large interlayer spacing (>3.2 nm), good thermal stability (decomposed at ~300°C) and improved surface properties for those dual-surfactant modified clays promoted a better dispersion of clays in polymer matrices and consequently better mechanical properties. For example, the tensile moduli of PP, PBT and PA 12 were improved from 515 MPa, 1065 MPa and 490 MPa to 1020 MPa, 1470 MPa and 800 MPa of their nanocomposites containing 3 wt% dual-surfactant modified clays, respectively. However, the dispersion of these organoclays varied in different polymer matrices, due to the different compatibility and the existence of polar type interactions between organoclays and polymer matrices. In order to further address the effect of polymer matrix on clay dispersion, three polyamide matrices (PA 6, PA 11 and PA 12) were employed, and PA 6 based nanocomposites showed the most effective exfoliation and mechanical enhancements due to the strong polar type interactions between the polymer and the organoclays.

Deep geological disposal remains the preferred option at present for the management of long-living and heat-emitting radioactive waste, which consists of confining the waste during a very long period (several hundreds of thousands of years) by placing them in a deep geological formation. Therefore, the understanding of the long-term behaviour of formations is becoming a key issue to ensure the feasibility of the geological disposal facilities, particularly regarding the generation and migration of gases. The present PhD work aims at better understanding the complex hydro-mechanical response of different argillaceous formations to gas migration process. To this end, gas flow through Boom Clay (one of the potential candidate plastic Paleogene clay formations to host nuclear waste in Belgium) has been deeply investigated on the basis of laboratory experiments at different scales and their numerical modelling. This main study has been complemented by presenting tests on two indurated and deeper claystone Mesozoicformations, considered as candidate host rocks in the Swiss programme for deep geological disposal, namely Opalinus Clay and ‘Brauner Dogger’. The different materials have been firstly characterised to evaluate mechanical (compressibility on loading) and two phase flow properties (water retention and permeability). Gas injection tests under oedometer and isotropic conditions have been performed following different testing protocols, in which boundary conditions have been carefully controlled. Major relevance has been given to restore the in situ stress state and to ensure full saturation conditions before the gas tests. Special emphasis has been placed in measuring sample deformation along the gas injection and dissipation process. The anisotropy of Boom Clay has been studied by carrying out tests with bedding planes parallel and normal to flow. Air injections have been performed at three different controlled-volume rates. The dissipation stages after shut-off have been also analysed to study air intrinsic permeability changes. Microstructure of samples before and after air injection tests has been evaluated by different techniques: mercury intrusion porosimetry, field-emission scanning electron microscopy and micro-focus Xray computed tomography. Gas migration turned out to be a fully coupled hydro-mechanical process. Air injection at constant stress induced expansion of the samples during pressure front propagation and compression during air pressure dissipation. The deformational behaviour was dependent on the injection rate. At slower injection rates expansion occurred during the injection while at higher rates it was delayed in time. Air intrinsic permeability resulted higher than water permeability suggesting that air flow took place along preferential pathways. Evaluation of the microstructural changes induced by air migration revealed the opening of fissures and allowed quantifying their apertures and separation, as well as their volume and connectivity. Air intrinsic permeability was found to be dependent on the fissured volume. To complete and better understand the gas transport mechanisms, numerical simulations of the experimental results have been performed using a fully coupled hydro-mechanical finite element code, which incorporates an embedded fracture permeability model to account for the correct simulation of the gas flow along preferential pathways. Clay intrinsic permeability and its retention curve have been made depend on strains through fracture aperture changes. Numerical results not only accounted for the correct simulation of the recorded upstream pressures and outflow volumes and pressures, but also for the volume change behaviour. The experimental and numerical information provided a good insight into the mechanisms of gas transport in deep clay formations and highlighted the role played by the deformational response on the air transport properties of argillaceous rock formations.
El almacenamiento geológico profundo es la solución actualmente aceptada para la gestión de los residuos radioactivos de alta actividad, que consiste en confinar dichos residuos durante un período muy largo de tiempo (varios cientos de miles de años) depositándolos en una formación geológica profunda. De ahí que el entendimiento del comportamiento a largo plazo se esté convirtiendo en una cuestión clave para asegurar la viabilidad de las instalaciones de almacenamiento de residuos, particularmente en lo que respecta a la generación y migración de gases. Este trabajo de doctorado tiene como objetivo mejorar la comprensión en lo que se refiere a la compleja respuesta hidro-mecánica de diferentes formaciones arcillosas frente a procesos de migración de gas. Con este objetivo, el flujo de gas a través de la arcilla Boom Clay (arcilla plástica del paleógeno candidata a alojar los residuos nucleares en Bélgica) se ha investigado en profundidad mediante experimentos de laboratorio a diferentes escalas y su modelación numérica. Este estudio principal se ha complementado con ensayos experimentales en dos formaciones arcillosas del mesozoico (más profundas y endurecidas),posibles candidatas a roca huésped en el programa suizo para el almacenamiento geológico profundo, llamadas Opalinus Clay y 'Brauner Dogger'. Inicialmente, los diferentes materiales han sido caracterizados para evaluar sus propiedades mecánicas (compresibilidad en carga) e hidráulicas (retención de agua y permeabilidad). Los ensayos de inyección de gas, bajo condiciones edométricas e isótropas, se han realizado siguiendo diferentes protocolos de ensayo controlando cuidadosamente las condiciones de contorno, así como, dando prioridad al hecho de restaurar el estado tensional in situ y las condiciones de saturación antes de los ensayos de gas. Además, se ha hecho especial hincapié en la medición de la deformación de las muestras a lo largo de los procesos de inyección y disipación de gas. La anisotropía de la Boom Clay se ha tenido en cuenta realizando ensayos con los planos de estratificación dispuestos en paralelo y perpendicular al flujo. Las inyecciones de aire se han realizado a tres velocidades volumétricas diferentes. Las etapas de disipación se han analizado para evaluar los cambios en la permeabilidad intrínseca al aire. La microestructura de las muestras se ha evaluado antes y después de los ensayos de inyección de aire mediante tres técnicas diferentes: porosimetría de intrusión de mercurio, microscopía electrónica de barrido de emisión de campo y micro-tomografía computarizada La migración de gases en estas rocas arcillosas saturadas resultó ser un proceso hidro-mecánico totalmente acoplado. La inyección de aire a tensión constante produjo expansión de las muestras durante la propagación del frente de presión y compresión durante la disipación de la presión de aire. El comportamiento deformacional dependió de la velocidad de inyección. A velocidades de inyección más lentas, la expansión se produjo durante la inyección, mientras que, a velocidades más altas, ésta se retrasó en el tiempo. La permeabilidad intrínseca al aire resultó ser más alta que la permeabilidad al agua medida, lo que sugiere que el flujo de aire tuvo lugar a lo largo de vías preferenciales. La evaluación de los cambios microestructurales inducidos por la migración de aire reveló la apertura de fisuras, cuantificando sus aperturas y separación, así como su volumen y conectividad, lo que permitió encontrar una relación de dependencia entre la permeabilidad intrínseca al aire y el volumen fisurado. Para completar la información experimental y comprender mejor los mecanismos de transporte de gas, se realizaron simulaciones numéricas de los resultados experimentales utilizando un código de elementos finitos acoplado, que incorpora un modelo de permeabilidad con fracturas embebidas para explicar el flujo de gas a lo largo de vías preferenciales. La permeabilidad intrínseca de la arcilla y su curva de retención dependen de la deformación a través de cambios en la apertura de la fractura. Los resultados numéricos no sólo reprodujeron de forma correcta las presiones registradas y los volúmenes de salida, sino también el comportamiento deformacional. Esta información experimental y numérica proporcionó una buena visión de los mecanismos de transporte de gas en formaciones arcillosas profundas y en los que destacó el papel desempeñado por la respuesta deformacional sobre las propiedades de transporte de aire.

Polymer clay nanocomposites (PCN) of poly(methyl methacrylate) (PMMA) and clay, were synthesised in-situ using a free radical suspension polymerisation technique. The weight fraction of clay in the PCN was systematically varied in order to understand the effect of clay on the physical properties of the resulting PCNs. However, unexpectedly it was found that the weight fraction of clay had a dramatic impact upon the molecular weight of the polymer matrix and a relationship between clay concentration and polymer molecular weight was established. Furthermore, it was also found that the change in molecular weight was dependent upon the clay type. Three different clay types were investigated; an organically modified montmorillonite (Cloisite 15a), a synthetic clay (Laponite RD) and a PEO modified Laponite RD. To produce the modified Laponite RD, mono amino PEO was synthesised via anionic polymerisation using dimethyl ethanol amine as an initiator. The modification of the Laponite RD clay took place in the reaction flask prior to the suspension polymerisation of the PCN. The PCN were characterised using size exclusion chromatography (SEC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and oscillatory shear rheology. Morphological studies of the PCN showed that the extent of clay dispersion depended on the clay type. Within the PMMA/Laponite RD nanocomposites an unusual network structure was formed, which appeared to be continuous throughout the material. Thermal properties of the PCN were investigated using DSC, TGA and Microcalorimetry. From oscillatory shear rheology, the full master curves for the PCN were obtained by applying the time-temperature superposition (TTS) principle. To quantify the effect of the clay upon the rheology, the experimental data was compared to the time dependent diffusion model of Des Cloizeaux for polydisperse polymer melts, which enables polydispersity to be incorporated through the use of the molecular weight distribution obtained via SEC.

The focus of the creative project was the artist exploration of altered forms and ash glaze techniques, as well as developing a new aesthetic of breaking free of old approaches, thus allowing him to express his emotions through the ceramic vessels. He developed and refined his technique of surface treatment on the vessels as he progressed through this project. His exploration into this new world of freedom helped him grow as an artist and emotionally.The artist desired to become a utilitarian potter at the beginning of his undergraduate studies but when he was introduced to the works of Paul Soldner, Peter Volkos, and Robert Piepenburg his interest in their works fueled his desire to expand his style of work. This lead to his exploration into altered vessels.
Department of Art

Polymer-clay nanocomposites are attracting global interest principally because property enhancements are obtained at low clay particle loadings (1-5 wt%). However there is lack of fundamental understanding of such composites. The aim of this work is to provide an insight into the interaction between polymer and clay. This includes the driving force for intercalation, the reinforcement mechanisms and property-volume fraction relationships. Functionalised poly(ethylene glycol)-clay, poly(c-caprolactone)-clay and thermoplastic starch-clay nanocomposites with a range of polymer molecular weights, clay volume fractions and with different clays were prepared using solution methods, melt-processing methods, and in situ polymerisation. A reliable X-ray diffraction technique for low angle basal plane spacing of clay, the essential parameter for structure determination, was established obtaining ±0.005 Mn between three diffractometers. The basal plane spacing was found to be unaffected by polymer molecular weight and preparation method but was affected by the nature of the polymer and clay. Increasing clay loading could lead to a lower spacing. As a cautionary observation, poly(ethylene glycol) with high molecular weight (2: 10,000) was found to undergo degradation readily during preparation of nanocomposites with and without clay. Competitive sorption experiments for molecular weight showed that high molecular weight fractions of polymer intercalate preferentially into clay during solution preparation. Thermodynamic studies on the intercalation process found that significant enthalpic change occurred during intercalation, which is coincident with the observation that heat-treated clays without interlayer water can intercalate polymer. The calculation of true volume fraction against nominal volume fraction provided reasonable explanation of property enhancement and helps understand the relation between nanocomposites and conventional composites. At a given clay loading, nanocomposites with better dispersion gave more property enhancement than those with lower dispersion or conventional composites. The crystallinity of semicrystalline polymer was also affected by varying extents of dispersion of clay. The use of X-ray diffraction with an internal standard was explored for quantitative analysis of intercalation and exfoliation.

The artist discusses the background, ideas, and work entitled Archetypes in Clay, for the completion of her Bachelor of Arts Degree and undergraduate research for the Fine and Performing Arts Scholar program at East Tennessee State University. The artist used this development of work to explore personality types, and how they can be portrayed through clay vessels. In particular, the artist shows her work, how she created the vessels, the testing involved, and the struggles she faced. Archetypes is the focus behind the concept of this project. Her work includes four ceramic vessels, created with clay and finished with glaze. The artist cites Carl Jung, Isabel Briggs-Myers, and NERIS Analytics Limited as important research in this project.

A series of quaternarized ammonium mono and di-cations, quaternarized amino acid ester mono and di-cations, and quaternarized polyammonium cations were synthesized by methylation reaction. The synthesized quaternarized ammonium derivatives were incorporated into the interlamellar space of the smectites, montmorillonite (SWy-1) and hectorite (SHCa-1). The adsorption of these quaternarized ammonium cations by the smectites were studied by colorimetric and Na-electrode methods. Also the CEC values were determined from the adsorption isotherms and were found to be close to the CECs of the smectites. The intercalation of the quaternarized ammonium cations into the interlamellar space of the smectites were evaluated by X-ray powder diffraction technique and the changes of the interlayer spacings upon intercalation were measured. The adsorption and X-ray results indicated that the quaternarized ammonium cations adopt a parallel orientation arrangement in the interlamellar space of the smectites. Insight into the micropore structure of the prepared organo-smectites has been obtained with N$\sb2$ adsorption and desorption studies. The BET interlayer surface area, external surface area, micropore volume and mesopore volume were calculated from the N$\sb2$ adsorption and desorption isotherms. The total BET surface areas of the organo-smectites were in the range of 58-224 m$\sp2$/g, depending on the size of the intercalated cations. It has been implied that the incorporation of the quaternarized ammonium cations into the interlamellar space of the smectites results in a microporous material with a network of cavities whose height and volume are controlled by the size and the shape of the organic cation. The gas chromatographic properties of these organo-smectites have been determined with focus on the separation of air, CH$\sb4$ and CO$\sb2$ as well as the separation of C$\sb1$-C$\sb4$ and C$\sb5$-C$\sb8$ hydrocarbons. The organo-smectites have been proven to be a GC adsorbent for gas separations. The separation of methane and carbon dioxide was controlled by the interactions with the clay surface, not by the interaction with the substituents of the alkylammonium chain. The shapes of the microcavities played a role in the separation of gas mixtures. The CO$\sb2$ retention time has been found to increase with increasing the free surface area of the organo-smectite. Moreover, it has been shown that the retention time of C$\sb1$-C$\sb4$ hydrocarbons decreased with increasing the free volume of the organo-smectite. Furthermore, some microporous organo-smectite materials have been imbedded into the cross-linked polydimethylsiloxane (PDMS) polymers giving composite membranes. The composite membranes have been evaluated by the gas permeation experiments. The pure gas permeation results showed that the gas permeabilities decreased upon filling of the organo-smectites into the PDMS polymers. The pure gas permeability ratios of O$\sb2$/N$\sb2$ and CO$\sb2$/CH$\sb4$ were found to be controlled by both the organo-smectite content and the microporosity of the organo-smectites. The maximum pure gas permeability ratio for CO$\sb2$/CH$\sb4$ achieved was 8.7 as compared to 3.9 which was obtained for organo-smectite free PDMS membranes.

The main purpose of this thesis is the development of a new constitutive soil model emphasising the use of thermodynamic principles. This new approach to plasticity modelling, termed ‘hyperplasticity’, was first developed by Collins and Houlsby (1997) and Houlsby and Puzrin (2000). This idea has been further extended to continuous hyperplasticity in which smooth transitions between elastic and plastic behaviour can be modelled (Puzrin and Houlsby, 2001b). Applying hyperplasticity to this research, a kinematic hardening model specified by means of two scalar functionals is used to accommodate the effect of stress history on stiffness. A rate-dependent calculation for an approximation of the incremental stress-strain response is introduced. The model developed in the research is named ‘kinematic hardening modified Cam-clay (KHMCC) model’ and requires eight parameters (plus an extra parameter for rate-dependent analysis). Triaxial test results from the Asian Institute of Technology (AIT) and cyclic undrained triaxial data from Chulalongkorn University are employed to establish the soil parameters for the new model. The model is initially developed in terms of triaxial stress-strain parameters for the purpose of comparison with the experimental data on Bangkok clay. The model is expressed in FORTRAN code for implementation into the OXFEM finite element program. Two examples of real geotechnical projects in Bangkok (a road embankment and tunnelling in soft ground) are analysed under plane strain conditions. Comparisons of the numerical analysis results with field data are made. In addition, factors affecting the results of the analysis such as stress history and K0, are investigated.

Clay consolidation has generally been considered from a macro-scale perspective by measuring the macro-scale compression of a clay soil over time. Clay particles in consolidation tests experience shear and normal forces at the inter-particle level due to force applied to the soil at the macro-scale. These shear and normal forces cause the particles to slide at the micro-scale and produce macro-scale changes in soil volume and shape. By considering the inter-particle interactions at the micro-scale, the shear force - normal force - velocity relationship can be described by the Rate Process Theory (RPT). This research investigated the use of the RPT for analyzing sliding at individual clay particle contacts during secondary compression to describe macro-scale clay behavior. The novel micro-scale friction experiments conducted in this research demonstrated that an Atomic Force Microscope (AFM) can be used to obtain coefficient of friction (μ) measurements for montmorillonite. This method allows for the measurements to be performed over spatial scales of a few microns, can be done under dry conditions or a wide range of aqueous solutions, and requires no calibration beyond making a few microscopic measurements of the probe. Control tests of silica on mica (μ = 0.29 ± 0.02) agree with literature values where limits indicate one standard deviation.μ values for wet and dry sodium montmorillonite were determined to be 0.20 ± 0.03 and 0.72 ± 0.03, respectively. The micro-scale AFM and macro-scale triaxial shear, ring shear, and direct shear experimental data ofμ as a function of sliding velocity were found to match well with those calculated using common RPT parameter values. The activation energy for the macro-scale triaxial shear and corresponding micro-scale friction regime experiments fall within the expected range for pure montmorillonite of 84–109 kJ/mol. Additionally, the micro-scale and macro-scale experimental results fall within the expected range for the number of bonds per unit of normal force of 10^7–10^9 bonds/N. A discrete element method (DEM) model was developed to calculate thin, disk-shaped clay particle movement in three dimensions during compression using the RPT as a contact model. The DEM compression results were compared to macro-scale consolidation experiments conducted on the same reference clay as the micro-scale AFM experiments. The influences on the compression of the number of bonds at each clay contact per unit of normal contact force and the activation energy were quantified. Increasing the activation energy decreased the compression, as expected. Similarly, increasing the number of bonds per unit of normal force at the contacts decreased the compression, as expected. Realistic clay fabrics with varying particle sizes, particle size distributions, and aspect ratios led to a compression model with behavior similar to the macro-scale laboratory compression tests. This research provides evidence of the close correspondence between macro-scale and micro-scaleμ measurements and contributes to multi-disciplinary understanding of factors that control friction between clay particles and deformation of clay masses. The results from this work can be applied to a wide range of time-dependent phenomena such as clay secondary compression, shear deformation, and fault dynamics behavior.
Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 243-251).
Fracture mechanics has been used for many years to study the mechanical behavior of brittle and quasi-brittle materials like concrete, rock, wood, and ceramics. To date, the application of fracture mechanics to soils has been limited to dry and partially saturated soils where soil consistency changes due to suction and tends to be harder exhibiting a quasi-brittle behavior. Of late, studying fracture propagation in clays and mudrocks has become of interest as it provides a means to extract oil from oil bearing strata. While crack initiation in soils can be analyzed using basic soil mechanics theories, development and propagation of a crack is energy driven and requires application of fracture mechanics principles. An essential parameter in Linear Elastic Fracture Mechanics (LEFM), the main analytical tool in studying fracture in rock, is the critical stress intensity factor that defines stress concentration near a crack tip beyond which a fracture would propagate. The basic mode of crack loading can be obtained by applying a normal stress that has a corresponding opening mode of crack surface displacement, called mode-I (tensile mode), with a critical stress intensity factor termed fracture toughness, denoted by KIC. In this experimental research, KIC is measured indirectly using a modified Brazilian Test configuration where load is applied normally on flattened Brazilian disk specimens without the need to introduce a flaw into the specimen. Intact natural specimens from four different deposits; Boston Blue clay, San Francisco Bay Mud, Presumpscot Maine clay, and Gulf of Mexico clay; are tested in oven-dried state under atmospheric conditions. In addition, two Clay-like materials; molded Gypsum and Plaster of Paris; have been investigated. Based on the analysis of the test data, the relation between mode I fracture toughness and tensile strength for the six tested materials agrees to a great extent with reported trends in the literature even for different fracture toughness and tensile strength testing techniques and for wider tested range of soils, rocks, geomaterials, clay-like, and rock-like materials. However, no clear relation between mode I fracture toughness and elastic modulus or any other physical parameter was determined.
by Shehab Sherif Wissa Agaiby.
S.M.

Digital Clay is a tactile array of linear fluidic actuators which provide distributed sensing and position control through the use of an embedded position sensor. The actuator implementation is achieved by two-way hydraulically-driven pistons which are integrated with computer controlled valves. Each actuator is connected to an underlying base plate which is in fluidic communication with high and low pressure reservoirs. The research focuses on the aspects of the fluidics necessary to operate the actuators and control actuation of Digital Clay. The main objectives of this work are the characterization of the fluid flow through the system and the design and implementation of an embedded inductance-based position sensor. Each actuator in Digital Clay is individually addressable and is controlled through the use of a closed-loop proportional integral controller with position feedback from the embedded inductance-based sensor. Also presented in this work is the characterization of an individual fluidic actuator and the realization of a 5x5 tactile array of actuators.

As far as is known, this is the first study to concentrate on the microstructural deformation of clay is undrained shear. The material was naturally dispersed; and it had been expected that during pre-peak deformation the platy clay particles would slip and turn to form large domains (i.e. groups of sub-parallel particles) inclined at 45o or more, although other hypotheses were also under consideration. Both optical microscopy and electron microscopy showed that the preferred orientation, which was originally horizontal, definitely remained horizontal whilst the shear strain increased, until the failure plane cut through the orientated structure. It was expected that when strongly anisotropic clay samples are deformed, the shear strain will disrupt the structure, so that the strength of anisotropy decreases. Conversely, when isotropic clay samples are deformed, it was expected that slippage of the particles will cause the strength of anisotropy to increase. The present samples started at a moderate strength of anisotropy, and the subsequent changes were small. This observation supports the above hypothesis and suggests that the examples were on the borderline between the two types of behaviour. There were, however, some changes of the microstructure. The strength of anisotropy at first appeared to increase and later to decrease as strain increased. The deviations of the orientations of the individual structural elements appeared to decrease at first and later to increase, this being the complementary trend. In addition, post-peak, the between-samples standard deviations increased with strain, suggesting that different samples were deforming in different ways. These results suggest that in normally consolidated undrained shear there may be three mechanisms acting within these samples, i.e. they were bedding down at first, and later being disrupted by the shear strains; but the failure plane cut through all pre-existing structure non-conformably. Further, there may have been an element of instability in the microstructural response to strain. The results available for the outer series of tests led to broadly similar conclusions.

This paper is about my relationship to the material clay, and how it has affected my creative process. In this text I argue that clay is a material with human properties. I think of my practice as a dialogue between me and the material, an exchange rather than a monologue. This is how I picture clay as my main partner for discussing the deeper questions of what it is to be human, how clay as material can stand as metaphor for what it is to be living. I argue that clay has the poetic strength to communicate these questions of life of a more existential nature. Through the argument of clay being a material with human properties, I reason that a practice in materiality is a study of empathy since we spend much time with our materials to fully grasp how they behave. I firmly believe that this world is in need of an empathic movement, and I think that the field of craft has the possibility to be part of that movement. I see practitioners within the field of craft as practitioners of the sometimes irrational, emotional and indescribable parts of life. As researchers of the more existential qualities of life, I believe that we are important voices in a society that is getting more focused on rationality. With some help from writers, practitioners and philosophers within and outside the field of craft, I reason around the following research question: Can a material based practice stand as lodestar in todays society, to show empathy towards each other as beings as well as our surroundings?

A study of clay chemistry has been approached with three aims: - to modify the conducting properties by intercalation of tetrathiafulvalene, - to study the electrochemistry of redox-active coordination compounds immobilised on clay coated electrodes, and - to study the role of clays as reagents in inorganic glass forming reactions using mainly solid-state magic-angle-spinning NMR. TTF was intercalated by smectites containing different interlayer and lattice cations. Evidence from ESR and 57Fe Mossbauer indicated charge-transfer from TTF to structural iron in natural montmorillonite, and to interlayer Cu2+ in Cu2+ exchanged laponite. No charge transfer was observed for laponite (Na+ form) itself. Ion exchange of TTF3(BF4)2 with laponite was found to proceed quantitatively. The intercalated species were believed to be (TTF)2+ dimers. Conductivity data showed an order of magnitude increase for the intercalated clays. The mechanism is thought to be ionic rather than CT as Na+ laponite showed a similar enhancement in conductivity. Mechanically robust colloidal clay films were prepared on platinum electrodes. After immersion in solutions containing redox active complexes [Co(bpy)3]3+ and [Cr(bpy)3]3+, the films became electroactive when a potential was applied. Cyclic voltammograms obtained for both complexes were found to be of the diffusion controlled type. For [Co(bpy)3]3+ immobilised on clay coated electrodes, a one-step oxidation and four-step reduction wave was observed corresponding to a one electron stepwise reversible reduction of Co(III), through Co(II), Co(I), Co(O) to Co(I) oxidation state. For [Cr(bpy)3]3+ the electrochemistry was complicated by the presence of additional waves corresponding to the dissociation of [Cr(bpy)3]3+ into the diaquo complex. ESR and diffuse reflectance data supported such a mechanism. 29Si, 27Al and 23Na MAS NMR spectroscopy, supported by powder XRD and FTIR, was used to probe the role of clays as reagents in glass forming reactions. 29Si MAS NMR was found to be a very sensitive technique for identifying the presence and relative abundance of crystalline and non-crystalline phases. In thermal reactions of laponite formation of new mineral phases such as forsterite, akermanite, sillimanite and diopside were detected. The relative abundance of each phase was dependent on thermal history, chemical nature and concentration of the modifier oxide present. In continuing work, the effect of selected oxides on the glass forming reactions of a model feldspar composition was investigated using solid state NMR alone. Addition of network modifying oxides generally produced less negative 29Si chemical shifts and larger linewidths corresponding to a wider distribution of Si-O-Si bond angles and lengths, and a dominant aluminosilicate phase with a less polymerised structure than the starting material. 29Si linewidths and 27Al chemical shifts were respectively correlated with cationic potential and Lewis acidity of the oxide cations. Anomalous Al(4) chemical shifts were thought to be due to precipitation of aluminate phases rather than a breakdown in Lowenstein's aluminium avoidance principle.

Swelling clays cause tremendous amounts of damage to infrastructure. For the effective prevention of detrimental effects of these clays, and to optimize the beneficial properties for industrial applications it is necessary to clearly understand the fundamental mechanisms of swelling of clays. In this study, we studied the effect of fluid polarity on swelling and flow properties of swelling clays using molecular modeling and experimental technique for bridging the molecular level phenomenon of these clays with microstructure change, particle breakdown and macro scale swelling and flow properties. A wide range of fluids (Dielectric Constant 110 to 2.4) were used, those are also commonly present in landfill leachates. We were able to tie the properties of swelling clays at different length scales. Then, we simulated the solvation of clay sheets, studied the effect of discrete charge distribution, contribution of edge charges on swelling clays and discussed some fundamental assumptions associated with double layer theories.
Department of Civil Engineering, North Dakota State University

Polymer/clay nanocomposites consisting of an epoxy resin matrix filled with organoclays have been investigated. The main objective of this study was to determine which combination of components led to the greatest enhancement in properties of the epoxy resin. Exfoliation of the clay was desired, as exfoliated nanocomposites are known to exhibit great improvements in mechanical properties [1]. The epoxy resins studied were di-functional DGEBA and tetra-functional TGDDM. The epoxy resin was cured with three different hardeners, these included: the high functionality amine hardener, TETA, and two anhydride hardeners, accelerated MTHPA and pure HHPA. The three organoclays used, contained alkylammonium cations and were also compared to the unmodified clay. Morphology was investigated by XRD and TEM, and the flexural properties of the resulting nanocomposites were studied. The effect that the addition of an organoclay has on the cure of the epoxy resin was investigated using MDSC. Both the temperatures required to cure the resin with, and without, the clay, and any changes in the total heat flow that occurred were studied. The Tg�++ of the cured nanocomposites was also measured using MDSC. The heat flow results indicated that the clays added to the epoxy resins act as a physical barrier, which prevents the resin from reaching full cure. In the higher functional resin, the addition of clay resulted in a significant decrease in the total heat flow, suggesting that a large amount of epoxy remains uncured, and, as a result, there should be a reduction in the amount of cross-linking. The lower cross-link density led to a significantly lower Tg and the mechanical properties were also poorer. The reactivity of the hardener towards the resin was found to have the greatest impact on the cured nanocomposite morphology. Intragallery polymerisation occurring at a faster rate than the extragallery polymerisation causes exfoliation. In order to achieve a balance that favours intragallery polymerisation, it was found that the curing reaction was required to be catalysed by the alkylammonium cation of the organoclay, and not catalysed by other means. The DGEBA cured with HHPA provided the largest layer expansion in the clay structure due to the alkylammonium cation catalysing the anhydride ring-opening reaction. The effect was not seen with TGDDM due to the tertiary amine in its structure. The accelerator within the MTHPA assisted extragallery polymerisation of the resin and the TETA cured readily without additional catalysis.

Polymer/clay nanocomposites consisting of an epoxy resin matrix filled with organoclays have been investigated. The main objective of this study was to determine which combination of components led to the greatest enhancement in properties of the epoxy resin. Exfoliation of the clay was desired, as exfoliated nanocomposites are known to exhibit great improvements in mechanical properties [1]. The epoxy resins studied were di-functional DGEBA and tetra-functional TGDDM. The epoxy resin was cured with three different hardeners, these included: the high functionality amine hardener, TETA, and two anhydride hardeners, accelerated MTHPA and pure HHPA. The three organoclays used, contained alkylammonium cations and were also compared to the unmodified clay. Morphology was investigated by XRD and TEM, and the flexural properties of the resulting nanocomposites were studied. The effect that the addition of an organoclay has on the cure of the epoxy resin was investigated using MDSC. Both the temperatures required to cure the resin with, and without, the clay, and any changes in the total heat flow that occurred were studied. The Tg++ of the cured nanocomposites was also measured using MDSC. The heat flow results indicated that the clays added to the epoxy resins act as a physical barrier, which prevents the resin from reaching full cure. In the higher functional resin, the addition of clay resulted in a significant decrease in the total heat flow, suggesting that a large amount of epoxy remains uncured, and, as a result, there should be a reduction in the amount of cross-linking. The lower cross-link density led to a significantly lower Tg and the mechanical properties were also poorer. The reactivity of the hardener towards the resin was found to have the greatest impact on the cured nanocomposite morphology. Intragallery polymerisation occurring at a faster rate than the extragallery polymerisation causes exfoliation. In order to achieve a balance that favours intragallery polymerisation, it was found that the curing reaction was required to be catalysed by the alkylammonium cation of the organoclay, and not catalysed by other means. The DGEBA cured with HHPA provided the largest layer expansion in the clay structure due to the alkylammonium cation catalysing the anhydride ring-opening reaction. The effect was not seen with TGDDM due to the tertiary amine in its structure. The accelerator within the MTHPA assisted extragallery polymerisation of the resin and the TETA cured readily without additional catalysis.

The objective of the work described in this thesis was to understand sorption reactions of uranium occurring at the water-clay mineral interfaces in the presence and absence of arsenic and other inorganic ligands. Uranium(VI) removal by clay minerals is influenced by a large number of factors including: type of clay mineral, pH, ionic strength, partial pressure of CO2, load of the sorbent, total amount of U present, and the presence of arsenate and other inorganic ligands such as sulfate, carbonate, and phosphate. Both sulfate and carbonate reduced uranium sorption onto IBECO bentonite due to the competition between SO42- or CO32- ions and the uranyl ion for sorption sites, or the formation of uranyl-sulfate or uranyl-carbonate complexes. Phosphate is a successful ligand to promote U(VI) removal from the aqueous solution through formation of ternary surface complexes with a surface site of bentonite. In terms of the type of clay mineral used, KGa-1b and KGa-2 kaolinites showed much greater uranium sorption than the other clay minerals (STx-1b, SWy-2, and IBECO montmorillonites) due to more aluminol sites available, which have higher affinity toward uranium than silanol sites. Sorption of uranium on montmorillonites showed a distinct dependency on sodium concentrations because of the effective competition between uranyl and sodium ions, whereas less significant differences in sorption were found for kaolinite. A multisite layer surface complexation model was able to account for U uptake on different clay minerals under a wide range of experimental conditions. The model involved eight surface reactions binding to aluminol and silanol edge sites of montmorillonite and to aluminol and titanol surface sites of kaolinite, respectively. The sorption constants were determined from the experimental data by using the parameter estimation code PEST together with PHREEQC. The PEST- PHREEQC approach indicated an extremely powerful tool compared to FITEQL. In column experiments, U(VI) was also significantly retarded due to adsorptive interaction with the porous media, requiring hundreds of pore volumes to achieve breakthrough. Concerning the U(VI) desorption, columns packed with STx-1b and SWy-2 exhibited irreversible sorption, whereas columns packed with KGa-1b and KGa-2 demonstrated slow, but complete desorption. Furthermore, most phenomena observed in batch experiments were recognized in the column experiments, too. The affinity of uranium to clay minerals was higher than that of arsenate. In systems containing uranium and arsenate, the period required to achieve the breakthrough in all columns was significantly longer when the solution was adjusted to pH 6, due to the formation of the uranyl-arsenate complex. In contrast, when pH was adjusted to 3, competitive sorption for U(VI) and As(V) accelerated the breakthrough for both elements. Finally, experiments without sorbing material conducted for higher concentrations of uranium and arsenic showed no loss of total arsenic and uranium in non-filtered samples. In contrast, significant loss was observed after filtration probably indicating the precipitation of a U/As 1:1 phase.

Pottery is a kind of craft which requires retentive training. The only way to achieve each technique is to practice in repetition till the skill has been absorbed into the hands and body of the practitioner. The most obvious problematic achievement in pottery skill is ‘wheel throwing’ technique. With the long history in straight forward training, one needs to free the mind and allow oneself be a ‘copy machine’ in order to learn the technique properly. The paradox of traditional practice of having mastered the skill, but could not break through, is one of typical obstruction to many crafters. ‘Flood’ as theme for investigation in clay was an attempt to set up a method in order to find the ‘breaking through’ in term of ‘thinking’ and ‘making’ for traditional pottery practitioner to be relevant in the pace of contemporary surrounding. The investigation was planned to de‐familiarize my perception over my tradition and practice, and it was an eye‐opening to how I positioned myself personally and professionally to the discipline, the society and the world.

An experimental and theoretical study of froth flotation separation of kaolinite from other associated minerals of china clay is presented herein. A new laboratory flotation equipment has been designed and built for the above study. Its novel features are discussed. Effects of physico-chemical variables such as pH, initial solid concentration of feed, froth height and air flowrate are studied by systematically carrying out series of semi-batch kinetic experiments. pH is shown to influence both recovery and grade of the product. The effects of pH are interpreted in terms of particle/particle interactions leading to flocculation which is demonstrated to be an essential prerequisite for flotation of small particles approaching colloidal size range with the typically 1-2mm bubbles produced in the cell. Regions in a flotation cell where hydrodynamic conditions permit flocculation are identified by an analysis of pulp flow based on a distributed shear rate model. The effects of initial solid concentration on recovery and grade are interpreted in terms of floc/bubble collision frequency. Influence of floc breakup and solid drainage on pulp phase and recovery kinetics, and product grade is discussed. Pulp phase kinetics are analysed on the basis of rate-distributed species model. The selective nature of froth drainage is demonstrated by a series of kinetic experiments using different froth heights. Air flowrate can influence both pulp phase kinetics and froth drainage. These effects are studied independently by conducting two sets of experiments - one with a negligible depth of froth and the other with a deep froth. An analysis of flow and rupture forces in the froth leads to identification of two distinct zones where different floc breakup and drainage mechanisms exist. On this basis a three-phase model, consisting of a mixed pulp phase and two mixed froth phases, is developed and used to predict froth effects on flotation kinetics and selectivity.

Temperature changes occur in soils in a number of ways, e. g. landfill liners, around buried services and during sampling. An experimental programme was conducted to examine the effect of temperature (between 10 to 80 °C) on the volume change and shear behaviour of saturated clays. Testing included Liquid Limit (cone penetrometer), residual shear strength (modified Bromhead Ring Shear), laboratory vane shear ( at moisture contents between the Liquid and Plastic Limits) and oedometer tests. An extensive literature survey indicated that kaolinites and smectites would show extremes of thermal behaviour. To examine this two artificially pure clays were tested: English China Clay (a well crystallised kaolinite) and Wyoming Bentonite (a monovalent smectite). To supplement this four British soils were tested: Keuper Marl, Lower Lias Clay, London Clay and Oxford Clay. Full material data were obtained coupled with careful control of stress and thermal histories. It is concluded that two types of extreme thermal response exists: a thermomechanical and a thermo-physicochemical change exhibited by kaolinite and smectite respectively. The temperature sensitivity of clays relative to a particular parameter is positively related to its specific surface area. A quick and repeatable method to qualitatively assess this has been developed: the LUT method. Its advantages include that no temperature calibrations are needed and it has a relatively large operating temperature range, 10 to 80 °C having been successfully used. The consolidation pressure (in the oedometer) needed to change the nature of a soil's thermal response is negatively related to its specific surface area. This, it is postulated, occurs at the same 'critical' contact stress for all clays, i. e. the interparticle threshold stress at which a thermo-physicochemical response changes to a thermo-mechanical one. This threshold stress occurs at a anisotropic consolidation pressure of 60 kPa for a well crystallised kaolinite , at 250 kPa for reconstituted London Clay and at 480 kPa for a mono-valent smectite. Furthermore, greater parallel particle alignment or reconstituting a sample enhances a soil's temperature sensitivity in the oedometer. The thermal changes to consolidation and permeability coefficients can be typically predicted by the corresponding change to the dynamic viscosity of water. Deviations occur with smectites at normal stresses greater than 480 kPa, while for Keuper Marl this occurred at normal stresses of 50 kPa and greater than 850 kPa. Keuper Marl exhibits a greater temperature sensitivity of different parameters than predicted by index tests. This is strongly dependent on consolidation pressure and temperature. At elevated temperatures (>40 °C) and under increasing consolidation pressure, ped units tend to collapse, but once the pressure is removed ped reformation occurs. Thus knowledge of thermal and stress histories, coupled with full material data, is essential to effectively predict temperature effects on the engineering behaviour of soils with any degree of confidence.

The application of chemical ground improvement using the electrokinetic stabilisation(EKS)method has the potential to overcome problems soft highly compressibility soil. This technique has the potential to enhance the strength and reduce compressibility of a wide range of soils. The aim of this study was to evaluate the use of EKS as an effective method to strengthen soft clay soils. A detailed laboratory programme of work was conducted using the initial base model developed by Liaki (2006). This study was conducted in two stages using laboratory scale models, using an inactive kaolinite clay. The test model using reusable Electrokinetic Geosythentics (EKG) developed at the Newcastle University to apply a constant voltage gradient of 50 V/m across a soil sample approximately 400 mm. The first stage involved testing of a ‘pure’ system with distilled water as the main pore electrolyte fluid supplied under zero hydraulic gradient conditions for periods of 3, 7 and 14 days. The second stage repeated test using calcium chloride and distilled water (CaCl-DW), DW and sodium silicate (DW-NaSiO) and CaCl-NaSiO, at the anode and cathode, respectively. Throughout both physical and chemical characteristics were measured. This enabled assessment of the design and configuration that could be used in the field together with a number of key limitations. The data presented herein enables a fuller understanding of the mechanisms contributing to the improvements achieved and how effective monitoring through the use of relatively simple test, e.g. pH and Atterberg Limits, can be achieved. Specifically cation exchange was considered to be the main mechanism causing a significant increase in shear strength observed for the CaCl-DW system with the increase seen to be more uniform across the soil sample for a period up to 14 days. This was supported by results of Atterberg limits,.

Thesis (Ph. D.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Civil Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

New findings about the geology of London Clay (King, 1981) have highlighted the importance of investigating the relationship between geology and engineering behaviour for stratified soils. Recent events, such as the Heathrow tunnel collapse in 1994 and the poorly predicted ground movements at St. James Park during the construction of the Jubilee line extension have also highlighted a local need to revise the general proprieties of the material with which engineers in London deal. This research aimed at finding a framework for the London Clay relating the engineering proprieties of this material to its geological features. High quality samples from different depths in London Clay were tested in their intact and reconstituted states using oedometer and advanced triaxial apparatus. The lithological units of the London Clay at the site have been accounted for in analysing the mechanical response of the clay. The structure and the nature of the clay from different strata were investigated microscopically and correlated with its large and small strain mechanical response. Shallower units showed a more open structure and higher clay content than deeper units. Samples from the same units had the same mechanical behaviour and engineering parameters, regardless their depth within the stratum, but differences were found between the different units, which reflected the differences in the nature and structure of clay from each stratum. The behaviour in both compression and shearing seemed to be dominated by the structure of the clay as well as by its nature, so that clay from units having a more packed and orientated structure showed a stiffer response and higher strengths than the clay from units with a more open structure. The behaviour of the clay was also investigated in the elastic region and the elastic parameters confirmed the effects of lithology on sample behaviour.