Les liens qui unissent la structure et les propriétés physiques, chimiques des matériaux sont très importants. En particulier, le degré d’ordre, les défauts cristallins, l’hétérogénéité structurale ou chimique, s’avèrent être des paramètres très pertinents dans la réactivité des matériaux. Ce travail a porté sur l’étude de la réactivité de plusieurs formes de la silice, et permet de montrer l’influence de l’ordre et de la cristallinité sur les processus de vieillissement par la réaction alcali-silice. Dans cette objectif, la réactivité de trois matériaux différents : granulats (silex), quartz et verre de silice a été suivie par différentes techniques d’investigations.Le quartz réagit très lentement, le verre très vite et le granulat de manière intermédiaire. Une analyse plus fine montre que la fraction mal cristallisée, voire amorphe, du granulat réagit préférentiellement.Le caractère désordonné des matériaux suggère l’utilisation de techniques sensibles à l’ordre local : nous avons employé, la spectroscopie d’absorption X (XANES et EXAFS) complétée par la RMN du solide.Les cartographies chimiques obtenues par microscopie électronique (en balayage et en transmission) ou au synchrotron montrent que le potassium K+ diffuse le premier et que le calcium Ca++ pénètre difficilement la structure cristalline de la silice. A l’échelle locale la RMN du silicium montre la dépolymérisation du réseau permet la diffusion des cations Ca++.Le micro-XANES révèle la présence de plusieurs environnements autour des atomes de silicium. L’un consiste en un silicium avec quatre oxygènes premiers voisins et l’autre avec moins de quatre atomes d’oxygènes. D’autre part, l’EXAFS montre l’absence du Ca et/ou K au niveau de la deuxième couche de voisins de l’atome de silicium absorbeur dans un environnement ordonné. / The relationships between the structure and the physical and chemical properties are very important in materials. In particular, the degree of order, the crystal defects and the structural heterogeneities or chemical parameters appear to play a key role in the reactivity of materials. This work is devoted to the study of the reactivity of silica-based materials, and shows of the influence of ordering and crystallinity on the sensitivity to the alkali silica reaction. In this perspective, the reactivity of three different materials: silica glass, aggregates (Flint) and quartz was followed by various techniques. Quartz reacts very slowly whereas the silica glass reacts very quickly, the aggregate exhibiting an intermediate behavior. A closer analysis shows that the amorphous or poorly crystalline fraction of the aggregate reacts preferentially. The role played by these poorly crystalline fractions suggests the use of techniques sensitive to short and medium range order such as: X-ray absorption spectroscopy (XANES and EXAFS) and solid state NMR. Chemical maps obtained by electron microscopy (scanning or in transmission) or at the synchrotron, show that the potassium K+ is the first to diffuse and that penetration of calcium Ca++ is more sluggish in crystalline silica. Locally, silicon NMR analysis shows that depolymerization of the crystalline lattice allows further penetration of calcium. The micro-XANES reveals the presence of several environments around silicon atoms. One exhibits four oxygen first neighbours and the other has less than four oxygen atoms around the silicon. On the other hand, the EXAFS shows the absence of Ca or K in the second layer of neighbouring silicon atom absorber. These results help to advance the understanding of reaction mechanisms occurring in the aggregate altered by the reaction

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Geological Sciences and Environmental Studies, 2007. / Includes bibliographical references.

Thesis (Ph.D.)--McMaster University (Canada), 1988. / Source: Dissertation Abstracts International, Volume: 62-13, Section: A, page: 0000.

Thesis (M.S.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 32-34).

To reduce CO2 emissions the cement industry has for decades diluted the Portland cement fraction of concrete binders with Supplementary Cementitious Materials (SCM). Defining the reactivity of these aluminosilicate-based materials and their interaction with clinker phases has however challenged the research community and limited their replacement levels. In the present study, to quantify the reactivity of SCMs during early hydration, aluminosilicate glasses with compositions representative of blast furnace slag and fly ash systems were synthesised and exposed to different activator solutions in a continuously stirred closed system reactor for a period up to 3 h. Solution compositions were measured from the very first minutes of dissolution with complementary solid surface analysis. The experimental conditions were designed to avoid precipitation, however an initial Ca maximum in the first 30 min of exposure to the activating solution was a common feature in most dissolution profiles with a subsequent rapid decline, most likely attributable to Ca-reincorporation on the reacting surface. Surface specific analysis confirmed Ca enrichment on the surface and also detected Al enrichment, suggesting the formation of a Ca-modified aluminosilicate phase by a dissolution reprecipitation mechanism on the surface of the glass. Differing chemistries are thought to be responsible for the Ca and Al re-integration on the reacting surface depending on the pH of the solution; near-neutral conditions favour Ca-readsorption and surface condensation reactions, whereas alkaline solutions favour Ca-reintegration via covalently bound phases. The Ca concentration in solution was also observed to control glass alteration. Decreased dissolution rates were in fact observed as Ca concentrations in solution were increased supporting the formation of a C-A-S-H phase on the surface, the formation of which was instead suppressed when a Ca chelating chelating agent (EDTA) was added to the solution resulting in increased glass dissolution. Experiments using in situ AFM and LAOICPOMS are also reported and the significance of the findings to the early hydration reactions of a blended cement system is discussed.

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Understanding PGE geochemistry in low abundance (i.e. sub ppb level) geological samples has been hampered by the absence of an accurate, low blank, preconcentration technique. Ni- S fire assay, the traditional preconcentration method, has been critically assessed and combined with isotope dilution to enable reproducible analysis of standards in the 1-l0ppb concentration range. In addition, a new anion exchange chromatography, low blank, isotope dilution method has been developed that allows analysis of Re, Os, Ir, Ru, Ft and Pd, at pg levels, from the same sample aliquot by ICP-MS. This method enables PGE abundances and Os isotopic ratios to be determined on the same sample dissolution, permitting geochronological studies. Samples are digested in Carius tubes and total procedural blanks are routinely less than l0pg/g for all elements, except Pt (25pg/g). Reproducibility is sufficient at the lOppt level to confidently identify inter-element PGE fractionations. Using this anion exchange preconcentration technique, PGEs have been characterised in a suite of plume-generated picrites from West Greenland, and a suite of subduction-related lavas, including fractionation series from Grenada (Lesser Antilles arc) and from Izu-Bonin. PGE concentrations are higher within the picrites of West Greenland, than in the picrites of Grenada, or boninites of Izu-Bonin. This is attributed to higher degrees of melting and less fractionation during West Greenland magma genesis. There is similarity in the PGE-pattems between all environments suggesting that relative PGE behaviour is not greatly altered during mantle melting in a subduction zone vs a plume. Subtle differences occur in inter-PGE ratios between the different environments and within the fractionation suites. Os and Ir do not behave in an analogous manner during fractionation indicating "compatibility" with different crystallising phases. The PGEs are associated with olivine fractionation in all of the primitive rock types, but, may also be compatible with other phases (e.g. magnetite/chromite/amphibole) during high-level fractionation in arc magma chambers. The PGE signatures in the evolved arc rocks are controlled by multi-stage fractionation. PGE concentrations decrease as fractionation progresses, except for Re and Ru. PGE compatibility during arc-lava fractionation decreases in the order Os>Ir>Pt>Pd>Ru>Re. There is not a strong sulfide control on PGE fractionation in any of the rock suites analysed, probably because the primary melts were generally S- undersaturated. This places important constraints on the nature of the mantle in the different tectonic environments. Os-isotopic studies indicate the presence of a radiogenic component in both the West Greenland picrite plume source region (recycled crust or outer core material) and the Grenada picrite source region (slab-derived fluids).

Typescript (photocopy) Includes bibliographical references (leaves 247-270)

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.