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Through flume experiments we demonstrate the calcite precipitation process seen at geothermal hot springs in the lab setting. A series of four experiments were run, varying temperature and terrace ridge height while all other experimental parameters, including initial substrate slope, spring water discharge, and CO₂ input were kept constant. The goal of the experiments was to measure the temperature and terrace height control quantitatively in terms of the amount of overall travertine aggradation, aggradation rate changes in time and downstream direction, as well as to observe the effect of these parameters on processes occurring during precipitation. Using the final deposit thickness measured manually at the end of each experiment and elevation data obtained from a laser topographic profiler, I conclude that high temperature and small terrace heights favor increased precipitation of travertine. However, the amount of precipitation also depends on location within a terrace pond. Flow velocity increases as it approaches a terrace lip, resulting in enhanced precipitation and greater thicknesses in the downstream direction through increased CO₂ degassing, a process called downstream coarsening. / text

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In many occupations such as welding, workers are exposed to a combination of several hazards. One of these is the exposure to fumes, particularly those produced from welding processes involving electrical arcs. The inhalation of welding fume can cause both temporary side effects and longer term health complications. These health effects lower the productivity and quality of life of the welder which in turn costs the employer through reduced worker productivity and potential compensation. Current techniques of fume measurement determine bulk quantity of formation without regard to fume plume dissipation into the work place. While some research has been conducted into dissipation, measurements near the welding arc have proven difficult and either numerical or salt water modelling have been used. Such modelling aims to replicate the welding process but is ultimately detached from the actual welding variables involved and does not provide data on fume concentration. Since welder exposure is determined by both fume concentration and dissipation into the workplace measurement techniques which could provide both would be considered highly desirable. In the field of combustion research a number of different laser techniques are used to image soot particulates in flames. These techniques include laser scattering, laser extinction and laser induced incandescence. As yet none of these techniques have found application to the measurement or imaging of particulate matter in arc welding fume plumes. In the work presented here these techniques have been investigated for welding fume measurements of concentration and dissipation. Laser scattering was used successfully to image the fume plume close to the welding arc of actual gas metal and flux cored arc welding processes. The resulting images provided relative fume concentration maps that were quantified when combined with measurements from laser extinction. Laser induced incandescence, while successfully applied to the imaging of soot concentration in flames, was found to have limited capabilities when applied to welding fume particulates. Fume box measurements were undertaken for GMAW and FCAW to determine actual FFR in response to changes in welding variables. The results were in general agreement with those obtained from laser techniques and referenced in literature. The fume plume images collected from in-situ laser measurements were compared with those from previous modelling of plume shape, radial spread and virtual origin. Laser diagnostics demonstrated a number of capabilities not available with traditional fume measurements. The findings of this research provide unique insight into fume dissipation. Such findings can be applied to minimise the quantity of fume, the transmission to the breathing zone and ultimately worker exposure in the workplace. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1339888 / Thesis (Ph.D.) - University of Adelaide, School of Mechanical Engineering, 2008

Supplementary cementitious materials (SCMs), are beneficial when used as partial replacement of cement in concrete mixtures for coastal concrete structures, blended with Portland cement (binary or ternary mixes), i.e., high-performance concrete provides improved properties when exposed to marine harsh environment. In order to characterize selected durability properties of different concrete mixtures, a testing program was established. The intent of this study consists of testing 10cm diameter x 20cm long concrete specimens prepared with a range of different mix designs. 1) to evaluate the rate of water absorption due to capillary suction, referred to as sorptivity, 2) to evaluate the concrete surface resistivity, 3) to evaluate and compare the total porosity of specimens with different mixes, and 4) to obtain correlations between resistivity and sorptivity. All of these experimental tests were carried out according to ASTM International Standards (Sorptivity, Porosity) and Florida Method of Test (Resistivity). The tests were performed on concrete samples at various ages. Moreover, The results provided a fast and reasonable approximation of the concrete durability over time. Ordinary portland cement was partially replaced with supplementary cementitious materials including: fly ash (20%), silica fume (8%) and blast furnace slag (50%). These SCMs are highly effective in creating more durable concrete design mixtures. The water-to-cementitious (w/cm) ratios of 0.41 and 0.35 were investigated. The concrete that contains pozzolanic materials has demonstrated progress in extending the time for initiation of corrosion. The test results obtained indicate that the concurrent inclusion of fly ash and silica fume greatly reduced water penetration. The mixes containing slag also showed lower porosity and water absorption result, when compared to specimens containing fly ash only. Ternary concrete mixtures specimens showed much higher surface resistivity values than binary mixture specimens. These results suggest that reducing w/cm ratio, adding SCMs to concrete mixtures improved the concrete durability. The possibilities for the risks of corrosion initiation would be minimized (delayed) by prescriptive and then performance-based concrete blends with SCM materials optimized for service exposure in aggressive environments. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

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Specimens from 27 batches of concrete with water to cementitious (cement plus silica fume) ratio of 0.25 to 0.32, with and without entrained air, were tested for freeze-thaw durability in accordance with ASTM C666, procedure A (freezing and thawing in water). In addition, another set of similar specimens were moist cured for 28 days instead of 14 days and tested in accordance with ASTM C666 , Procedure A to determine the effect of curing time on the freeze-thaw durability of high strength concrete. Results show that non air-entrained high strength concrete with water cementitious ratio of less than 0.30, regardless of the length of curing time, is frost resistant. Non-air-entrained concrete with water-cement ratio of 0.32 is also durable if silica fume is not used. / Ph. D.

A tecnologia dos materiais a base de cimento Portland vem se desenvolvendo rapidamente, onde a melhoria das propriedades mecânicas vem sendo alcançada, eliminando os agregados graúdos e estudando a composição granulométrica da mistura, procurando preencher os vazios utilizando materiais finos e ultrafinos, como pó de quartzo e a sílica ativa. Esta pesquisa tem como objetivos: desenvolver concreto de pós reativos com resistência à compressão próxima de 200 MPa e módulo de elasticidade acima de 45 GPa; propor uma relação constitutiva para o material, considerando o volume de fibras; especificar as deformações máximas na tração e na compressão; e verificar a influência das fibras nas resistências à compressão e à tração na flexão. Para isso, foi utilizado o método de empacotamento das partículas sólidas, com o intuito de definir composições granulométricas, e desenvolveu-se técnicas necessárias para a moldagem, adensamento e cura térmica. A análise experimental compreendeu o estudo das seguintes propriedades: resistência à compressão, módulo de elasticidade, resistência à tração na flexão, deformações e ductilidade. As fibras metálicas melhoraram as propriedades mecânicas e aumentaram a ductilidade do concreto. A temperatura de cura e o tempo de submissão ao tratamento térmico, tornou o material mais resistente. A deformação específica máxima na compressão foi definida experimentalmente como 4,3%. O limite elástico para as deformações de tração ficou em 0,28%. Foi proposta uma relação constitutiva para tensões de compressão, que pode ser utilizada para concretos de pós reativos, com resistência à compressão próxima de 200 MPa e taxa de fibras até 4% em volume. Os resultados obtidos indicam que o concreto de pós reativos desenvolvido apresentou altas resistências à compressão e à tração na flexão, onde a microestrutura do material mostrou-se com baixíssima porosidade e interface pasta - agregado praticamente suprimida. A tecnologia desenvolvida nesta pesquisa pode ser considerada um grande avanço na tecnologia de materiais a base de cimento Portland que, com maiores aperfeiçoamentos, espera-se a aplicação desse material em situações que tirem proveito das excelentes propriedades mecânicas e durabilidade / The technology of Portland cement materials has developed quickly, where the improvement of the mechanical properties has been reached, eliminating the coarse aggregates and studying the granular mixture, in order to fill the emptiness with fine and ultra-fine materials, like crushed quartz and silica fume. The present paper aimed: develop reactive powder concrete with compressive strength close to 200 MPa and module of elasticity above 45 GPa; propose a strength x strain relationship in compression for the material considering the volume of fibers; specify the maximum strain in the traction and in the compression; and to verify the influence of the fibers in the compression strength and in the bending strength. It went using the method of packing of the solid particles to define the grain size distribution, and necessary techniques were developed for the preparation and thermal cure. The experimental analysis understood the study of the following properties: compression strength, module of elasticity, bending strength, strain and ductility. The metallic fibers improved the mechanical properties and they increased the ductility of the concrete. The cure temperature and the time of submission to the thermal treatment, improved the compression strength. The maximum strain in the compression was defined experimentally as 4,3%. The elastic limit for the traction strain was 0,28%. A strength x strain relationship in compression was proposed, and can be used in reactive powders concrete, with compression strength of around 200 MPa and rate of fibers of up to 4% of volume. The results indicate that the reactive powders concrete developed presented excellent compression strength and bending strength, and the material presented a microestrutura with low porosity. The technology developed in this research can be considered a great progress in the technology of materials with Portland cement, and the application of that material is expected in situations that use advantage of the excellent mechanical properties and durability