Mineral carbonation contributes to CO2 reduction, and it may also reduce the cost of mineral processing by improving the mechanical properties of rock/ore. Here, we study and compare the mechanical properties of two minerals, forsterite (Mg2SiO4) and magnesite (MgCO3) using molecular dynamics (MD) simulation. The goal is to understand whether carbonation results in hardness reduction of rock and subsequently comminution energy during the crushing and processing of the ore. We investigated how these materials respond to different physical conditions, such as temperature and strain rate, to understand their behavior under stress. By examining the molecular structure of forsterite and magnesite at temperatures ranging from 300K to 700K and strain rates of 0.001, 0.01, and 0.05ps-1, we observed how they deform when subjected to both tensile and compressive forces. This study has shown that at higher temperatures, both forsterite and magnesite monocrystals undergo deformation more easily under pressure. Forsterite is found relatively hard and shows maximum strength before deformation compared to magnesite. The stiffness of magnesite decreases at elevated temperatures which reduces the energy requirement for the comminution process. We also looked at how pressure and temperature changes affected their elasticity. Ultimately, our findings suggest that magnesite may be more suitable for processes like comminution, which involves breaking down materials, compared to forsterite. This insight into the effects of mineral carbonation on geomaterials contributes to our understanding of how these minerals behave under different conditions and could have implications for various industries. / Master of Science / Mineral carbonation contributes to CO2 reduction, and it may also reduce the cost of mineral processing by improving the mechanical properties of rock/ore. Here, we study and compare the mechanical properties of two minerals, forsterite (Mg2SiO4) and magnesite (MgCO3) using molecular dynamics (MD) simulation. The goal is to understand whether carbonation results in hardness reduction of rock and subsequently comminution energy during the crushing and processing of the ore. We investigated how these materials respond to different physical conditions, such as temperature and strain rate, to understand their behavior under stress. By examining the molecular structure of forsterite and magnesite at temperatures ranging from 300K to 700K and strain rates of 0.001, 0.01, and 0.05ps-1, we observed how they deform when subjected to both tensile and compressive forces. This study has shown that at higher temperatures, both forsterite and magnesite monocrystals undergo deformation more easily under pressure. Forsterite is found relatively hard and shows maximum strength before deformation compared to magnesite. The stiffness of magnesite decreases at elevated temperatures which reduces the energy requirement for the comminution process. We also looked at how pressure and temperature changes affected their elasticity. Ultimately, our findings suggest that magnesite may be more suitable for processes like comminution, which involves breaking down materials, compared to forsterite. This insight into the effects of mineral carbonation on geomaterials contributes to our understanding of how these minerals behave under different conditions and could have implications for various industries.

Com o crescente uso de estruturas de membrana tensionada, as relações tensãodeformação do tecido utilizado em sua fabricação devem ser bem entendidas. Deste modo, esta dissertação apresenta um estudo sobre o comportamento mecânico de um tecido arquitetônico PTFE-vidro, ressaltando seu complexo mecanismo de deformação que engloba efeitos de anisotropia, não-linearidade física, troca de ondulações, histerese, remoção do espaçamento entre os fios e variação de temperatura. Diferentes métodos para modelagem do material foram estudados, com ênfase no modelo de material ortótropo representado por um funcional energia de deformação hiperelástico. Além disso, vários protocolos para ensaios de tração em tecidos recobertos foram analisados e uma série de ensaios biaxiais com amostras cruciformes foram realizados no Centro de Pesquisa e Desenvolvimento da Birdair, Inc. Um determinado funcional energia de deformação foi então ajustado aos dados de campo obtidos nestes testes, cujos resultados foram então comparados diretamente aos dados obtidos em campo e a um ajuste direto de uma superfície suave tensão-deformação. A performance do modelo ajustado não se encontra ainda em um patamar de aplicação industrial, entretanto este estudo permite um entendimento global dos mecanismos de deformação do tecido PTFEvidro, fornecendo também uma massa de dados consistentes que podem ser utilizados em situações práticas. / Considering the growing use of tensioned membrane structures, the stress-strain relation of the fabric used on its construction must be well understood. This dissertation presents a study of the mechanical behavior of a PTFE coated fiberglass fabric, emphasizing its complex strain mechanism which is influenced by the material anisotropy, physical non-linearity, crimp interchange, hysteresis, removal of yarn spacing and changes in temperature. Different material models were studied, focusing on an orthotropic material model represented by a hyperelastic strain energy function. Also, different test protocols were reviewed and a series of biaxial tests on cruciform samples were performed at the Birdair, Inc.s Research and Development Center. A strain energy function was adjusted to the collected data and than its results compared to the data itself and to another stress-strain function directly adjusted to the data. The performance of the strain-energy function chosen is not on a level of industrial application; however this study gives a global understanding of the PTFE coated fiberglass strain mechanism and also provides a consistent database that may be used on real situations.

Com o crescente uso de estruturas de membrana tensionada, as relações tensãodeformação do tecido utilizado em sua fabricação devem ser bem entendidas. Deste modo, esta dissertação apresenta um estudo sobre o comportamento mecânico de um tecido arquitetônico PTFE-vidro, ressaltando seu complexo mecanismo de deformação que engloba efeitos de anisotropia, não-linearidade física, troca de ondulações, histerese, remoção do espaçamento entre os fios e variação de temperatura. Diferentes métodos para modelagem do material foram estudados, com ênfase no modelo de material ortótropo representado por um funcional energia de deformação hiperelástico. Além disso, vários protocolos para ensaios de tração em tecidos recobertos foram analisados e uma série de ensaios biaxiais com amostras cruciformes foram realizados no Centro de Pesquisa e Desenvolvimento da Birdair, Inc. Um determinado funcional energia de deformação foi então ajustado aos dados de campo obtidos nestes testes, cujos resultados foram então comparados diretamente aos dados obtidos em campo e a um ajuste direto de uma superfície suave tensão-deformação. A performance do modelo ajustado não se encontra ainda em um patamar de aplicação industrial, entretanto este estudo permite um entendimento global dos mecanismos de deformação do tecido PTFEvidro, fornecendo também uma massa de dados consistentes que podem ser utilizados em situações práticas. / Considering the growing use of tensioned membrane structures, the stress-strain relation of the fabric used on its construction must be well understood. This dissertation presents a study of the mechanical behavior of a PTFE coated fiberglass fabric, emphasizing its complex strain mechanism which is influenced by the material anisotropy, physical non-linearity, crimp interchange, hysteresis, removal of yarn spacing and changes in temperature. Different material models were studied, focusing on an orthotropic material model represented by a hyperelastic strain energy function. Also, different test protocols were reviewed and a series of biaxial tests on cruciform samples were performed at the Birdair, Inc.s Research and Development Center. A strain energy function was adjusted to the collected data and than its results compared to the data itself and to another stress-strain function directly adjusted to the data. The performance of the strain-energy function chosen is not on a level of industrial application; however this study gives a global understanding of the PTFE coated fiberglass strain mechanism and also provides a consistent database that may be used on real situations.

Das Tragverhalten von Textilbeton ist stark nicht-linear und der Verlauf der Spannungs-Dehnungs-Beziehung hängt von zahlreichen Parametern ab. Unter einaxialer Zugbelastung existieren bereits umfangreiche experimentelle Untersuchungen und theoretische Modelle zur Beschreibung des Tragverhaltens. In vielen Anwendungen, z. B. bei Querkraft- und Torsionsbeanspruchung, sind die Beanspruchungen jedoch nicht einaxial und/oder nicht axial zur Bewehrungsrichtung, und es kommt zu Interaktionen der beiden Bewehrungshauptrichtungen, primär infolge des Einflusses zweier Risssysteme in den beiden Hauptrichtungen. Das Tragverhalten textiler AR-Glas- und Carbonbewehrungen unter zweiaxialen Zugbeanspruchungen wurde experimentell untersucht, um diese Einflüsse qualitativ und quantitativ beschreiben zu können. In diesem Beitrag werden erste Ergebnisse vorgestellt.

Das Tragverhalten von Textilbeton ist stark nicht-linear und der Verlauf der Spannungs-Dehnungs-Beziehung hängt von zahlreichen Parametern ab. Unter einaxialer Zugbelastung existieren bereits umfangreiche experimentelle Untersuchungen und theoretische Modelle zur Beschreibung des Tragverhaltens. In vielen Anwendungen, z. B. bei Querkraft- und Torsionsbeanspruchung, sind die Beanspruchungen jedoch nicht einaxial und/oder nicht axial zur Bewehrungsrichtung, und es kommt zu Interaktionen der beiden Bewehrungshauptrichtungen, primär infolge des Einflusses zweier Risssysteme in den beiden Hauptrichtungen. Das Tragverhalten textiler AR-Glas- und Carbonbewehrungen unter zweiaxialen Zugbeanspruchungen wurde experimentell untersucht, um diese Einflüsse qualitativ und quantitativ beschreiben zu können. In diesem Beitrag werden erste Ergebnisse vorgestellt.

[pt] O conhecimento do comportamento de solos residuais é de grande importância para projetos geotécnicos no Brasil e, em particular, na região do Rio de Janeiro, tendo em vista que o clima tropical e as características geológicas favorecem a ocorrência de mantos residuais de grande espessura. O presente trabalho trata do estudo do comportamento tensão-deformação de um solo residual proveniente de um perfil de alteração de rocha gnáissica do maciço da Tijuca, Rio de Janeiro. Como os solos residuais gnáissicos preservam as foliações herdadas da rocha matriz, investigou-se em particular a relevância de se considerar a ocorrência de anisotropia nas características de resistência e deformabilidade destes solos. No estudo foi utilizado o equipamento triaxial cúbico desenvolvido na PUC-Rio. Este equipamento possibilita o controle independente das três tensões principais, sendo mais adequado para a reprodução das trajetórias de tensões tridimensionais, usualmente associadas com obras geotécnicas no campo, e em particular, para estudos sobre as características de anisotropia de solos. O programa experimental constou de ensaios de compressão axial e hidrostática, sob condições drenadas de carregamento, utilizando o equipamento triaxial cúbico. Foram realizados também ensaios oedométricos convencionais, de modo a se obter as características de compressibilidade do solo. Foram moldados corpos de prova a partir de blocos indeformados, paralelos e perpendiculares à foliação observada no solo, o que possibilitou a análise dos resultados para direções distintas de carregamento. Para efeito de comparação sobre a relevância do arranjo estrutural dos grãos do solo, foram ensaiados também corpos de prova compactados dos mesmos materiais. A análise dos resultados permitiu a obtenção dos módulos de deformabilidade e dos parâmetros de resistência do solo residual. Em particular, foram verificados os efeitos da direção de carregamento dos corpos de prova, do nível das tensões de confinamento, do grau de intemperismo, do arranjo estrutural dos grãos e dos efeitos do grau de saturação. Pode-se concluir que os solos estudados não apresentaram efeitos marcantes de anisotropia nas características de resistência. No entanto, quanto à deformabilidade, pode-se considerar que o solo residual jovem apresentou características anisotrópicas. / [en] The knowledge of the mechanical behaviour of residual soils is of great importance in geotechnical projects, because of its abundance in tropical regions, such as Brazil and particularly in the area of Rio de Janeiro. The present work presents a study on the fundamental stress-strain behaviour of a residual soil resulting from a profile of a gneiss rock in Rio de Janeiro. As the gneiss residual soils preservethe bedding planes from the parent rock, the relevance of considering anisotropy in the stress- strain characteristics of these soils was investigated. The cubic triaxial equipment developed at PUC-Rio was used in this research. This equipment allows the independent control of the three principal stresses, allowing the reprodution of three-dimensional stress paths, usually associated with geotechnical works in the field. The experimental program consisted of axial and hidrostatic tests, under drained loading conditions, using the cubic triaxial equipment. One- dimensional oedometer tests were also performed, in order to obtain the compressibility characteristics of the residual soil. Undisturbed specimens were prepared with the bedding planes parallel or perpendicular to the loading direction. Analysis of the test results showed the effects of load direction, confining stress level, weathering degree, structural soil fabric and saturation degree. It may be concluded that the gneiss residual soils which were selected for this research do not present significant effects of anisotropy in the strength characteristics. In the stress- strain characteristics, however, it may be concluded that the young residual soil showed effects of anisotropy. / [es] EL conocimiento sobre el comportamiento de suelos residuales resulta de gran importancia para los proyectos geotécnicos en Brasil y, en particular, en la región de Rio de Janeiro, considerando que el clima tropical y las características geológicas favorecen la existencia de mantos residuales de gran espesor. El presente trabajo estudia el comportamiento tensión-deformación de un suelo residual proveniente de un perfil de alteración de roca gnáisica del macizo de la Tijuca, Rio de Janeiro. Como los suelos residuales gnáisicos preservan las foliaciones heredadas de la roca matriz, fue necesario estudiar si resultaba relevante considerar la aparición de anisotropía en las características de resistencia y deformabilidad de estos suelos. En el estudio se utilizó el equipo triaxial cúbico desarrollado en la PUC-Rio. Este equipo permite el control independente de las tres tensiones principales, siendo más adecuado para la reproducción de las trayectorias de tensiones tridimensionales, usualmente asociadas a obras geotécnicas en el campo, y en particular, para estudios sobre las características de anisotropía de suelos. El programa experimental incluyó ensayos de compresión axial e hidrostática, sobre condiciones drenadas de carga, utilizando el equipo triaxial cúbico. Fueron realizados también ensayos oedométricos convencionales, con el objetivo de obtener las características de compresibilidad del suelo. Fueron moldados cuerpos de prueba a partir de bloques no deformados, paralelos y perpendiculares a la foliación observada en el suelo, lo que permitió el análisis de los resultados para distintas direcciones de carga. Para efecto de comparación sobre la relevancia del arreglo extructural de los granos del suelo, se realizaron ensayos con cuerpos de prueba compactados de los mismos materiales. El análisis de los resultados permitió la obtención de los módulos de deformabilidad y de los parámetros de resistencia del suelo residual. En particular, se verificaron los efectos de la dirección de carga de los cuerpos de prueba, del nível de las tensiones de contensión, del grado de intemperización, de la disposición extructural de los granos y de los efectos del grado de saturación. Se puede concluir que los suelos estudiados no presentaran efectos marcantes de anisotropía en las características de resistencia. Sin embargo, con respecto a la deformabilidad, se puede considerar que el suelo residual joven presentó características anisotrópicas.

The overall objective of this study was to develop an optimised Ultra-High-Performance Concrete (UHPC) matrix based on the modified Andreasen and Andersen optimum particle packing model by using available South African materials. The focus of this study was to determine the optimum combined fibre and superplasticiser content for UHPC by using a response surface design. The UHPC was appropriately designed, produced and tested. Various changes in mechanical properties resulting from different combinations of steel fibre and superplasticiser contents was investigated. The flowability, density and mechanical properties of the designed UHPC were measured and analysed. Both the fibre and superplasticiser content play a significant role in the flowability of the fresh concrete. The addition of fibres significantly improved the strength of the concrete. The results show that the superplasticiser content can be increased if a more workable mix is required without decreasing the strength significantly. The statistical analysis of the response surface methodology confirms that the designed models can be used to navigate the design space defined by the Central Composite Design. The optimum combined fibre and superplasticiser content depend on the required mechanical properties and cost. Using the modified Andreasen and Andersen particle packing model and surface response design methodology, it is possible to efficiently produce a dense Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC) with a relatively low binder amount, low fibre content and good workability. The effect of heat curing on the mechanical properties was investigated. It was concluded that heat curing is not recommended when considering the long-term strength development. The estimated strength development of concrete obtained by using the fib Model Code 2010 (2013) does not incorporate the detrimental effect of high curing temperatures on long-term strength and therefore overestimate the long-term strengths. The strength estimates for both early and long-term ages can be improved by considering this effect in the strength development functions obtained from fib Model Code 2010 (2013). The effect of specimen size on the compressive and flexural tensile strength of UHPFRC members were established. It was found that the specimen size has a significant effect on the measured cube compressive strength. Smaller beam specimens showed higher ductility compared to those of the larger beam specimens. The crack width decreased as the beam’s depth decreased. A lower variability was experienced in the beams with limited depth (< 45 mm). Further testing is required to determine whether a span-to-depth ratio of 10 would yield optimum results. The utilisation of by-products, such as undensified silica fume and fly ash, as cement replacement materials makes UHPFRC sustainable, leading to a reduced life-cycle cost. The calculated Embodied Energy per unit strength (EE/unit strength) and Embodied Carbon per unit strength (EC/unit strength) values for the UHPFRC mixture yield lower values compared to that of the 30 MPa concrete mixture, indicating that UHPFRC can be used to reduce the environmental footprint of the concrete industry. The inverse analysis method used was successful in providing an improved simplified stress-strain response for the UHPFRC. The analysis provided valuable information into the stress-strain, load-deflection and moment-curvature responses of the UHPFRC. Standard material test results were used to theoretically calculate moment-curvature responses and were then compared to the experimental results obtained. The study demonstrated that it is possible to efficiently produce a dense and workable UHPFRC with relatively low binder amount and low fibre content. This can result in more cost-effective UHPFRC, thus improving the practical application thereof. / Dissertation (MEng)--University of Pretoria, 2020. / Civil Engineering / MEng (Structural engineering) / Unrestricted