abstract: Nuclear magnetic resonance (NMR) is an important phenomenon involving nuclear magnetic moments in magnetic field, which can provide much information about a wide range of materials, including their chemical composition, chemical environments and nuclear spin interactions. The NMR spectrometer has been extensively developed and used in many areas of research. In this thesis, studies in two different areas using NMR are presented. First, a new kind of nanoparticle, Gd(DTPA) intercalated layered double hydroxide (LDH), has been successfully synthesized in the laboratory of Prof. Dey in SEMTE at ASU. In Chapter II, the NMR relaxation studies of two types of LDH (Mg, Al-LDH and Zn, Al-LDH) are presented and the results show that when they are intercalated with Gd(DTPA) they have a higher relaxivity than current commercial magnetic resonance imaging (MRI) contrast agents, such as DTPA in water solution. So this material may be useful as an MRI contrast agent. Several conditions were examined, such as nanoparticle size, pH and intercalation percentage, to determine the optimal relaxivity of this nanoparticle. Further NMR studies and simulations were conducted to provide an explanation for the high relaxivity. Second, fly ash is a kind of cementitious material, which has been of great interest because, when activated by an alkaline solution, it exhibits the capability for replacing ordinary Portland cement as a concrete binder. However, the reaction of activated fly ash is not fully understood. In chapter III, pore structure and NMR studies of activated fly ash using different activators, including NaOH and KOH (4M and 8M) and Na/K silicate, are presented. The pore structure, degree of order and proportion of different components in the reaction product were obtained, which reveal much about the reaction and makeup of the final product. / Dissertation/Thesis / Ph.D. Physics 2013

L'objectif de la présente thèse et de développer un cadre d'étude et de simulation apte à prédire les propriétés effectives de diffusion dans les matériaux cimentaires saturés. Le principe suivi, fondé sur les approches multi-échelles séquencées, permettra de modéliser chaque échelle d'intérêt, depuis le gel des C-S-H, jusqu'au matériau béton, et ainsi via des simulations de prédire les coefficients de diffusion effectifs.Le cadre d'étude est donc fondé sur les points clés suivant :- Des morphologies de type "matrice - inclusion" sont générées via des excursions de champs aléatoires corrélés tri-dimensionnels. Cette approche, combinée avec quelques opérations morphologiques, permet la génération de morphologies inclusionnaires 3D suivant des distributions de tailles imposées. Il est ensuite possible de faire évoluer ces morphologies, depuis un état initial, en fonction d'un modèle prescrit (par exemple en termes de fraction volumiques), via le seuil de l'excursion.- Les cibles morphologiques de chaque échelle considérées tentent de refléter les résultats expérimentaux et modèles les plus communément admis. En supplément, à l'échelle de la pâte de ciment, un modèle "simple" d'hydratation est développé afin de prédire l'évolution de celle-ci dans le temps en termes de fractions volumiques. Le choix a été fait d'utiliser pour fondement un modèle simple (Jennings & Tennis), incorporant des paramètres essentiels, tels que la composition minéralogique du ciment ou le rapport e/c. Des modifications mineures ont été apporté au modèle, afin de prendre en compte de récents résultats expérimentaux, concernant principalement la fin de l'hydratation ainsi que sa cinétique.- Le cadre d'homogénéisation a été construit pour être utilisable à toutes les échelles considérées, et il permet ainsi de prédire les propriétés effectives de diffusion avec des considération énergétiques d'équivalence entre échelles. De façon analogue à la théorie de Hill pour l'élasticité, le cadre d'étude assure une séparation d'échelle cohérente vis-à-vis des propriétés effectives de diffusion.- Enfin, d'un point de vue numérique, les simulations utilisent les méthodes E-FEM, couplées à l'utilisation de maillages non-adaptés sur lesquels les morphologies sont "projetées". De cette façon, les discontinuités géométriques (discontinuité de propriétés matériaux) sont sont assurés par les élément finis enrichis, et ne requièrent pas d'éléments joint, ou de "moyennage" de propriétés.Les résultats de chaque échelle sont utilisés comme paramètres d'entrés pour les échelles suivantes. Depuis l'échelle des hydrates (C-S-H), jusqu'à l'échelle du béton, les coefficients de diffusion effectifs sont ainsi estimés. / The aim of the present Ph.D. is to develop a methodology and a simulation framework able to predict as accurately as possible effective properties regarding diffusion in saturated cement based materials. A sequenced multiscale framework is developed to perform numerical homogenization on diffusive properties, and thus predict effective properties. The general outline is to model every scale in concrete-like materials, from the C-S-H gel, to the concrete scale, and with the help of a proper framework, be able to predict effective properties. The methodology relies on the following key points for every considered scale :- Inclusion-matrix like morphologies are generated through level set methods applied to multi-dimensional correlated random fields. This approach, together with few morphological operations allows to generate 3D morphologies with given particle size distributions (PSD), or pore size distributions. Then, it is also possible, from the initial state, to make those morphologies evolve according to any descriptive model (e.g. in terms of volume fraction), via the level set.- The morphological description of each scale is chosen according to the most acknowledged experimentations and models. In addition, at the cement paste scale, a hydration model was developed to predict the evolution of the cement paste through time, in terms of volume fractions. The choice was made to keep a simple model (Jennings & Tennis), with few but essential input parameters (mineral cement composition, w/c ratio, PSD). It has only been modified to include recent experimental results, such as the maximal hydration degree, or the hydration rates.- The upscaling framework was built to suit every considered scale, and allows to assess effective properties based on energy conservation principles. Similar to Hill's theory for elasticity, the framework is build to ensure to proper scale separation regarding effective diffusion coefficients.- Lastely, the numerical context is based on E-FEM techniques, which allows to use unstructured meshes, on which the morphologies are projected. This way, any material discontinuity in dealt within the FE, and thus does not require averaging properties, or joint elements. Results from every scale will be used as inputs at the higher scales, and effective diffusion coefficients are thus estimated.

Hochduktiler Beton ist ein mit kurzen Kunststofffasern bewehrter Hochleistungs-verbundwerkstoff auf Zementbasis, der unter Zugbelastung eine hohe nichtelastische Verformbarkeit und ein verfestigendes Materialverhalten aufweist. Dieses Verhalten wird durch die Zugabe von diskontinuierlich verteilten Kurzfasern aus Kunststoff erzielt. In der vorliegenden Arbeit wurden einachsige Bauteilzugversuche durchgeführt auf deren Basis das globale und lokale Zugtragverhalten der großformatigen Versuchskörper beschrieben werden kann. Ausgangspunkt sind experimentelle Untersuchungen zum Tragverhalten des Stabstahls und des hochduktilen Betons sowie zu deren gemeinsamen Verbundverhalten. Die Untersuchungen zeigen, dass der Herstellungsprozess das Betongefüge und damit auch das mechanische Verhalten von hochduktilem Beton beeinflusst und dieser auf Grund seiner Zusammensetzung ein ausgeprägtes Schwindverhalten aufweist. Beides muss bei der Untersuchung großformatiger Versuchskörper berücksichtigt werden. Dazu wurden sowohl unbewehrte als auch bewehrte Dehnkörper mit unterschiedlichem Bewehrungsgehalt unter kontrollierten Herstellungsbedingungen in einem konventionellen Mischwerk hergestellt. Die Ergebnisse der experimentellen Untersuchung erlauben die Abbildung des Last-Verformungsverhaltens unter Berücksichtigung der hohen Schwindmaße durch isoliert ermittelte Spannungs-Dehnungs-Beziehungen des hochduktilen Betons und des reinen Stahls. Dieses Verfahren erlaubt eine einfache Beschreibung des kombinierten Tragverhaltens unter Berücksichtigung der rissüberbrückenden Wirkung der Fasern. / SHCC is an advanced construction material developed especially for strain-hardening, quasi-ductile behaviour. Both are achieved through the combined interaction of short polymer fibres dispersed in the cementitious matrix. The resulting tensile behaviour of SHCC is characterized by a progressive formation of multiple cracks and high strain capacity, which influences the structural behaviour especially in combination with steel reinforcement. This thesis reports on experimental investigations to analyse the load-bearing behaviour of R/SHCC members. The investigations included the determination of relevant material properties as well as uniaxial tension tests on steel reinforced slab elements. The aim was to study the effect of multiple cracking on the bond interaction with steel reinforcement and their combined load-deformation behaviour. Specific attention was also given to the influence of the production process and shrinkage behaviour of SHCC. It was shown that production and size related changes of material properties influence the cracking behaviour of SHCC, which can lead to a significant reduction of tensile strain capacity in a structural element. The interaction with steel reinforcement, on the other hand, was found to facilitate multiple cracking and enhance tensile strain capacity during the stage of elastic steel deformations. However, a mutual dependency of SHCC fracture and plastic steel deformations could be observed in the post-yielding stage of the steel rebar. The experimental results were discussed with respect to their implications for constitutive modelling of the tensile load-bearing behaviour. The resulting relationships are based upon the individual material behaviour as well as their bond interaction. Further to that, the effects of SHCC shrinkage and early strain-hardening of steel reinforcement were assessed based on the experimental data. These results contribute to the understanding of the mechanical processes in order to determine the behaviour of steel reinforced SHCC for practical applications.