Dissertations / Theses on the topic 'Mechanical carbonation'

The potential success of integrating mineral carbonation, as a pathway to CO₂ sequestration, in mining projects, is dependent on the mineralogical composition and characteristics of its waste rock and tailings. Ultramafic rocks have proven the best potential substrate for mineral carbonation and their ability to alter and to convert CO₂ into its carbonate mineral form is dependent on the original mineralogy and particle surface area. CO₂ conversion kinetics is complex and with the application of appropriate comminution technologies, its efficiency can be enhanced. The objective of this research is to evaluate mechanical activation to enhance the carbonation storage capacity of mine waste material. Three approaches were taken in this research. The first approach was to characterize the microstructure of the mechanically-activated mineral olivine, a predominant mineral constituent of ultramafic rocks, using X-ray diffraction patterns and line profile analysis methods with full pattern fitting method. The second approach was to compare the structural and chemical changes of mine waste with pure olivine, both of which were activated by various mechanical forces under both wet or dry conditions and subsequently carbonated in a direct aqueous carbonation process. Regardless of milling conditions, forsterite (Mg₂SiO₄), the olivine mineral variety in the mine waste, was found to be the main mineral being mechanically-activated and carbonated. It was determined that lizardite (Mg₃(Si₂O₅)(OH)₄), a hydrated magnesium silicate also common in ultramafic hosted mineral deposits, acted as catalyzer assisting forsterite reaching high levels of activation. This condition generated a greater CO₂ conversion to carbonate than that of pure olivine with the equal specific milling energy input. The stirred mill proved to be the most efficient form of mechanical activation vis-a-vis the direct aqueous carbonation process, followed by the planetary mill and the vibratory mill. The third approach analyzes the feasibility of mechanical activation in an integrated mineral carbonation process in a nickel mine considering the life cycle of the process. The minimum operating cost for 60% CO₂ sequestration efficiency was 105-107 $/t CO₂ avoided. At this point, the Turnagain project can potentially sequester 238 Mt/y CO₂ using its waste during the 28-year life of mine.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
This work comprises two studies on the evaluation of cement-coconut powder composite in curing and aging conditions. In the first study the composites were subjected to the accelerated carbonation process during the first 48 hours of cure, then were dried and subjected to curing conditions until saturated at 28 days. The results shows that the composites had a reduction in the water absorption and increased bulk density. The carbonated composites had a 26% increase in compression strength and 16% in the flexural strength as compared to no-carbonate composite. The interaction between the reduction of the Ca(OH)2 and increasing CaCO3 content was observed by thermogravimetric analysis. In the second study, the composites was evaluated by methods of external and internal natural aging for 6 months and by the accelerated carbonation for 84 days. Increased measurements from electrical resistivity and ultrasonic during cure age were related to the increase in the mechanical properties, reduction of porosity and hydration process of these composites. Three types of age showed similar mechanical and physical properties, the electrical resistivity measurements was related to the increase of CaCO3 content, verified by thermogravimetry. The different stages of this work the composites were characterized by X-ray diffraction, thermal analysis, scanning electron microscopy with energy dispersive spectroscopy and were evaluated for their physical and mechanical properties.
Este trabalho compreende dois estudos sobre a avaliação de compósitos cimento-pó de coco em condições de cura e de envelhecimento. No primeiro estudo, os compósitos foram submetidos ao processo de carbonatação acelerada durante as primeiras 48 horas de cura e, em seguida foram submetidos as condições de cura seca e saturada até 28 dias. Os resultados indicaram que os compósitos carbonatados tiverem uma absorção de água reduzida e aumento da densidade. Esses materiais apresentaram um aumento de 26% na resistência à compressão e de 16% no módulo de ruptura, em comparação com compósitos não carbonatados. A interação entre a diminuição do conteúdo de Ca(OH)2 e o aumento do teor de CaCO3 foi observada por análise termogravimétrica. No segundo estudo, os compósitos foram avaliados pelos métodos de envelhecimento natural externo e interno por até 6 meses, e pela carbonatação acelerada por até 84 dias. O aumento das medições de resistividade eléctrica e de ultrassom durante o período de cura foi relacionado com o aumento nas propriedades mecânicas, redução da porosidade e o processo de hidratação dos compósitos. Os três tipos de envelhecimento apresentaram propriedades físicas e mecânicas similares, as medidas de resistividade elétrica foram relacionadas com o aumento do teor de CaCO3 comprovado pela termogravimetria. Nas diferentes etapas do presente trabalho, os compósitos foram caracterizados por difração de raios X, análise térmica, microscopia eletrônica de varredura com espectroscopia por dispersão de energia e foram avaliadas as suas propriedades físicas e mecânicas.

[EN] The test for determining the resonance frequencies has traditionally been used to investigate the mechanical integrity of concrete cores, to assess the conformity of concrete constituents in different accelerated durability tests, and to ascertain constitutive properties such as the elastic modulus and the damping factor. This nondestructive technique has been quite appealed for evaluation of mechanical properties in all kinds of durability tests. The damage evolution is commonly assessed from the reduction of dynamic modulus which is produced as a result of any cracking process. However, the mechanical behavior of concrete is intrinsically nonlinear and hysteretic. As a result of a hysteretic stress-strain behavior, the elastic modulus is a function of the strain. In dynamic tests, the nonlinearity of the material is manifested by a decrease of the resonance frequencies, which is inversely proportional to the excitation amplitude. This phenomenon is commonly referred as fast dynamic effect. Once the dynamic excitation ceases, the material undergoes a relaxation process whereby the elastic modulus is restored to that at rest. This phenomenon is termed as slow dynamics. These phenomena (fast and slow dynamics) find their origin in the internal friction of the material. Therefore, in cement-based materials, the presence of microcracks and interfaces between its constituents plays an important role in the material nonlinearity. In the context of the assessment of concrete durability, the damage evolution is based on the increase of hysteresis, as a result of any cracking process. In this thesis three different nondestructive techniques are investigated, which use impacts for exciting the resonant frequencies. The first technique consists in determining the resonance frequencies over a range of impact forces. The technique is termed Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). It consists in ascertaining the downward resonant frequency shift that the material undergoes upon increasing excitation amplitude. The second technique consists in investigating the nonlinear behavior by analyzing the signal corresponding to a single impact. This is, to determine the instantaneous frequency, amplitude and attenuation variations corresponding to a single impact event. This technique is termed as Nonlinear Resonant Acoustic Single Impact Spectroscopy (NSIRAS). Two techniques are proposed to extract the nonlinear behavior by analyzing the instantaneous frequency variations and attenuation over the signal ring down. The first technique consists in discretizing the frequency variation with time through a Short-Time Fourier Transform (STFT) based analysis. The second technique consists of a least-squares fit of the vibration signals to a model that considers the frequency and attenuation variations over time. The third technique used in this thesis can be used for on-site evaluation of structures. The technique is based on the Dynamic Acousto- Elastic Test (DAET). The variations of elastic modulus as derived through NIRAS and NSIRAS techniques provide an average behavior and do not allow derivation of the elastic modulus variations over one vibration cycle. Currently, DAET technique is the only one capable to investigate the entire range of nonlinear phenomena in the material. Moreover, unlike other DAET approaches, this study uses a continuous wave source as probe. The use of a continuous wave allows investigation of the relative variations of the elastic modulus, as produced by an impact. Moreover, the experimental configuration allows one-sided inspection.
[ES] El ensayo de determinación de las frecuencias de resonancia ha sido tradicionalmente empleado para determinar la integridad mecánica de testigos de hormigón, en la evaluación de la conformidad de mezclas de hormigón en diversos ensayos de durabilidad, y en la terminación de propiedades constitutivas como son el módulo elástico y el factor de amortiguamiento. Esta técnica no destructiva ha sido ampliamente apelada para la evaluación de las propiedades mecánicas en todo tipo de ensayos de durabilidad. La evolución del daño es comúnmente evaluada a partir de la reducción del módulo dinámico, producido como resultado de cualquier proceso de fisuración. Sin embargo, el comportamiento mecánico del hormigón es intrínsecamente no lineal y presenta histéresis. Como resultado de un comportamiento tensión-deformación con histéresis, el módulo elástico depende de la deformación. En ensayos dinámicos, la no linealidad del material se manifiesta por una disminución de las frecuencias de resonancia, la cual es inversamente proporcional a la amplitud de excitación. Este fenómeno es normalmente denominado como dinámica rápida. Una vez la excitación cesa, el material experimenta un proceso de relajación por el cual, el módulo elástico es restaurado a aquel en situación de reposo. Este fenómeno es denominado como dinámica lenta. Estos fenómenos ¿dinámicas rápida y lenta¿ encuentran su origen en la fricción interna del material. Por tanto, en materiales basados en cemento, la presencia de microfisuras y las interfaces entre sus constituyentes juegan un rol importante en la no linealidad mecánica del material. En el contexto de evaluación de la durabilidad del hormigón, la evolución del daño está basada en el incremento de histéresis, como resultado de cualquier proceso de fisuración. En esta tesis se investigan tres técnicas diferentes las cuales utilizan el impacto como medio de excitación de las frecuencias de resonancia. La primera técnica consiste en determinar las frecuencias de resonancia a diferentes energías de impacto. La técnica es denominada en inglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Ésta consiste en relacionar el detrimento que el material experimenta en sus frecuencias de resonancia, con el aumento de la amplitud de la excitación. La segunda técnica consiste en investigar el comportamiento no lineal mediante el análisis de la señal correspondiente a un solo impacto. Ésta consiste en determinar las propiedades instantáneas de frecuencia, atenuación y amplitud. Esta técnica se denomina, en inglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Se proponen dos técnicas de extracción del comportamiento no lineal mediante el análisis de las variaciones instantáneas de frecuencia y atenuación. La primera técnica consiste en la discretización de la variación de la frecuencia con el tiempo, mediante un análisis basado en Short-Time Fourier Transform (STFT). La segunda técnica consiste en un ajuste por mínimos cuadrados de las señales de vibración a un modelo que considera las variaciones de frecuencia y atenuación con el tiempo. La tercera técnica empleada en esta tesis puede ser empleada para la evaluación de estructuras in situ. La técnica se trata de un ensayo acusto-elástico en régimen dinámico. En inglés Dynamic Acousto-Elastic Test (DAET). Las variaciones del módulo elástico obtenidas mediante los métodos NIRAS y NSIRAS proporcionan un comportamiento promedio y no permiten derivar las variaciones del módulo elástico en un solo ciclo de vibración. Actualmente, la técnica DAET es la única que permite investigar todo el rango de fenómenos no lineales en el material. Por otra parte, a diferencia de otras técnicas DAET, en este estudio se emplea como contraste una onda continua. El uso de una onda continua permite investigar las variaciones relativas del módulo elástico, para una señal transito
[CAT] L'assaig de determinació de les freqüències de ressonància ha sigut tradicionalment empleat per a determinar la integritat mecànica de testimonis de formigó, en l'avaluació de la conformitat de mescles de formigó en diversos assajos de durabilitat, i en la terminació de propietats constitutives com són el mòdul elàstic i el factor d'amortiment. Esta tècnica no destructiva ha sigut àmpliament apel·lada per a l'avaluació de les propietats mecàniques en tot tipus d'assajos de durabilitat. L'evolució del dany és comunament avaluada a partir de la reducció del mòdul dinàmic, produït com resultat de qualsevol procés de fisuración. No obstant això, el comportament mecànic del formigó és intrínsecament no lineal i presenta histèresi. Com resultat d'un comportament tensió-deformació amb histèresi, el mòdul elàstic depén de la deformació. En assajos dinàmics, la no linealitat del material es manifesta per una disminució de les freqüències de ressonància, la qual és inversament proporcional a l'amplitud d'excitació. Este fenomen és normalment denominat com a dinàmica ràpida. Una vegada l'excitació cessa, el material experimenta un procés de relaxació pel qual, el mòdul elàstic és restaurat a aquell en situació de repòs. Este fenomen és denominat com a dinàmica lenta. Estos fenòmens --dinámicas ràpida i lenta troben el seu origen en la fricció interna del material. Per tant, en materials basats en ciment, la presència de microfissures i les interfícies entre els seus constituents juguen un rol important en la no linealitat mecànica del material. En el context d'avaluació de la durabilitat del formigó, l'evolució del dany està basada en l'increment d'histèresi, com resultat de qualsevol procés de fisuración. En esta tesi s'investiguen tres tècniques diferents les quals utilitzen l'impacte com a mitjà d'excitació de les freqüències de ressonància. La primera tècnica consistix a determinar les freqüències de ressonància a diferents energies d'impacte. La tècnica és denominada en anglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Esta consistix a relacionar el detriment que el material experimenta en les seues freqüències de ressonància, amb l'augment de l'amplitud de l'excitació. La segona tècnica consistix a investigar el comportament no lineal per mitjà de l'anàlisi del senyal corresponent a un sol impacte. Esta consistix a determinar les propietats instantànies de freqüència, atenuació i amplitud. Esta tècnica es denomina, en anglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Es proposen dos tècniques d'extracció del comportament no lineal per mitjà de l'anàlisi de les variacions instantànies de freqüència i atenuació. La primera tècnica consistix en la discretización de la variació de la freqüència amb el temps, per mitjà d'una anàlisi basat en Short-Time Fourier Transform (STFT). La segona tècnica consistix en un ajust per mínims quadrats dels senyals de vibració a un model que considera les variacions de freqüència i atenuació amb el temps. La tercera tècnica empleada en esta tesi pot ser empleada per a l'avaluació d'estructures in situ. La tècnica es tracta d'un assaig acusto-elástico en règim dinàmic. En anglés Dynamic Acousto-Elastic Test (DAET). Les variacions del mòdul elàstic obtingudes per mitjà dels mètodes NIRAS i NSIRAS proporcionen un comportament mitjà i no permeten derivar les variacions del mòdul elàstic en un sol cicle de vibració. Actualment, la tècnica DAET és l'única que permet investigar tot el rang de fenòmens no lineals en el material. D'altra banda, a diferència d'altres tècniques DAET, en este estudi s'empra com contrast una ona contínua. L'ús d'una ona contínua permet investigar les variacions relatives del mòdul elàstic, per a un senyal transitori. A més, permet la inspecció d'elements per mitjà de l'accés per una sola cara.
Eiras Fernández, JN. (2016). Studies on nonlinear mechanical wave behavior to characterize cement based materials and its durability [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/71439
TESIS
Premiado

Etude bibliographique et experimentale de l'hydratation et de la carbonation du beton en dispersant dans la masse des polyisocyanates (hmdi ou mdi, qui accelerent l'hydratation, et ipdi, qui la retardent). Analyse des reactions. Resultats prometteurs de l'application de la technique pour ameliorer la stabilite de la teinte des betons colores, les resistances mecaniques a court terme, la tenue aux agents agressifs et la durabilite des fibres de verre dans une matrice de ciment

Non-stoichiometric strontium iron oxide is described by an abbreviated formula SrFeOx (2.5 ≤ x ≤ 3.0) exhibits a variety of interesting physical and chemical properties over a broad range of temperatures and in different gaseous environments. The oxide contains a mixture of iron in the trivalent and the rare tetravalent state. The material at elevated temperature is a mixed oxygen conductor and it, or its derivatives,can have practical applications in oxygen conducting devices such as pressure driven oxygen generators, partial oxidation reactors in electrodes for solid oxide fuel cells (SOFC). ¶ This thesis examines the behaviour of the material at ambient and elevated temperatures using a broad spectrum of solid state experimental techniques such as: x-ray and neutron powder diffraction,thermogravimetric and calorimetric methods,scanning electron microscopy and Mossbauer spectroscopy. Changes in the oxide were induced using conventional thermal treatment in various atmospheres as well as mechanical energy (ball milling). The first experimental chapter examines the formation of the ferrite from a mixture of reactants.It describes the chemical reactions and phase transitions that lead to the formation of the oxide. Ball milling of the reactants prior to annealing was found to eliminate transient phases from the reaction route and to increase the kinetics of the reaction at lower temperatures. Examination of the thermodynamics of iron oxide (hematite) used for the reactions led to a new route of synthesis of the ferrite frommagnetite and strontium carbonate.This chapter also explores the possibility of synthesis of the material at room temperature using ball milling. ¶ The ferrite strongly interacts with the gas phase so its behaviour was studied under different pressures of oxygen and in carbon dioxide.The changes in ferrite composition have an equilibrium character and depend on temperature and oxygen concentration in the atmosphere. Variations of the oxygen content x were described as a function of temperature and oxygen partial pressure, the results were used to plot an equilibrium composition diagram. The heat of oxidation was also measured as a function of temperature and oxygen partial pressure. ¶ Interaction of the ferrite with carbon dioxide below a critical temperature causes decomposition of the material to strontium carbonate and SrFe12O19 . The critical temperature depends on the partial pressure of CO2 and above the critical temperature the carbonate and SrFe12O19 are converted back into the ferrite.The resulting SrFe12O19 is very resistant towards carbonation and the thermal carbonation reaction does not lead to a complete decomposition of SrFeOx to hematite and strontium carbonate. ¶ The thermally induced oxidation and carbonation reactions cease at room temperature due to sluggish kinetics however,they can be carried out at ambient temperature using ball milling.The reaction routes for these processes are different from the thermal routes.The mechanical oxidation induces two or more concurrent reactions which lead to samples containing two or more phases. The mechanical carbonation on the other hand produces an unknown metastable iron carbonate and leads a complete decomposition of the ferrite to strontiumcarbonate and hematite. ¶ Thermally and mechanically oxidized samples were studied using Mossbauer spectroscopy. The author proposes a new interpretation of the Sr4Fe4O11 (x=2.75) and Sr8Fe8O23 (x=2.875)spectra.The interpretation is based on the chemistry of the compounds and provides a simpler explanation of the observed absorption lines.The Mossbauer results froma range of compositions revealed the roomtemperature phase behaviour of the ferrite also examined using x-ray diffraction. ¶ The high-temperature crystal structure of the ferrite was examined using neutron powder diffraction.The measurements were done at temperatures up to 1273K in argon and air atmospheres.The former atmosphere protects Sr2Fe2O5 (x=2.5) against oxidation and the measurements in air allowed variation of the composition of the oxide in the range 2.56 ≤ x ≤ 2.81. Sr2Fe2O5 is an antiferromagnet and undergoes phase transitions to the paramagnetic state at 692K and from the orthorhombic to the cubic structure around 1140K.The oxidized formof the ferrite also undergoes a transition to the high-temperature cubic form.The author proposes a new structural model for the cubic phase based on a unit cell with the Fm3c symmetry. The new model allows a description of the high-temperature cubic form of the ferrite as a solid solution of the composition end members.The results were used to draw a phase diagramfor the SrFeOx system. ¶ The last chapter summarizes the findings and suggests directions for further research.

Orientador: Renivaldo José dos Santos
Resumo: Durante o processo de fabricação dos artefatos de borracha natural (BN), é possível adicionar cargas, podendo ser combinadas em função das propriedades finais pretendidas. Nesse sentido o carbonato de cálcio vem sendo utilizado como carga de enchimento nas formulações com borracha natural, apenas para aumentar o volume da amostra para a mesma quantidade de borracha implementada, buscando apenas a redução do custo final. Devido a demanda industrial, surge a necessidade de investigar a possibilidade de fazer com que uma carga, ora antes utilizada como enchimento, passe a atuar como carga de reforço mecânico, ou seja, a realização de tratamentos superficiais se torna uma possibilidade viável, para que a carga consiga realizar ligações cruzadas entre as cadeias de carbono da BN. Dessa forma, foi proposto neste trabalho o estudo de compósitos de borracha natural tipo crepe claro com carbonato de cálcio ultrafino tratado com 2% do Chartwell C-515.71HR^® para substituição parcial da sílica comercial tratada com silano, buscando identificar a influência deste agente de acoplamento no processo de vulcanização, a fim de melhorar a interação entre a borracha natural e carbonato de cálcio ultrafino. O preparo ocorreu em um misturador aberto de cilindros com a variação de 10 em 10 phr para as cargas, nos híbridos, iniciou-se em 40/00 até 00/40 (sílica/carbonato de cálcio ultrafino), e foi produzida uma amostra controle, com a mesma formulação, porém sem carga, denominada goma pura. Foi po... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: During the manufacturing process of natural rubber (BN) artifacts, it is possible to add loads, which can be combined depending on the desired final properties. In this sense, calcium carbonate has been used as filler in formulations with natural rubber, just to increase the sample volume for the same amount of rubber implemented, seeking only to reduce the final cost. Due to industrial demand, there is a need to investigate the possibility of causing a load, previously used as a filler, to act as a mechanical reinforcement load, that is, the performance of surface treatments becomes a viable possibility, so that the cargo is able to cross-link the BN carbon chains. Thus, the main objective of this work is the study of natural rubber composites of light crepe type with ultrafine calcium carbonate treated with 2% of Chartwell C-515.71HR^® for partial replacement of commercial silica treated with silane, seeking to identify the influence of this coupling agent in the vulcanization process, in order to improve the interaction between natural rubber and ultrafine calcium carbonate. The preparation took place in an open cylinder mixer with a variation of 10 in 10 phr for the loads, in the hybrids, it started in 40/00 until 00/40 (silica / ultrafine calcium carbonate), and a control sample was produced , with the same formulation, but without load, called pure gum. It was possible to replace up to 75% of the silica with treated calcium carbonate, but the best response was to replac... (Complete abstract click electronic access below)
Mestre

The task of this diploma’s thesis was processing construction-technology project to revitalization the mining towers because of its current worsened state and subsequent adjustments for cultural activities.

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A partir dos últimos trinta anos, a difusão da alvenaria estrutural com o emprego de blocos cerâmicos passou a exigir destes últimos a capacidade de absorver esforços mecânicos provenientes do peso próprio das edificações e das sobrecargas a elas transmitidas. As pesquisas para a viabilização desta nova função dos blocos cerâmicos não foram, até o presente momento, tão intensas a ponto de garantirem de forma efetiva o seu bom desempenho estrutural, e alguns problemas relacionados com as suas propriedades mecânicas e expansão por umidade (EPU) passaram a evidenciar a necessidade do aprimoramento das suas características. Foi com tal propósito que nesta tese se desenvolveram algumas investigações voltadas à detecção de novos parâmetros que aumentassem o acervo de conhecimento da EPU e das propriedades mecânicas dos blocos cerâmicos e, em tal direcionamento, partiu-se de informações da literatura técnica relativas ao efeito benéfico dos óxidos de cálcio e de magnésio incorporados às massas tomadas como matérias-primas dos blocos cerâmicos. Os resultados obtidos com corpos-de-prova autoclavados permitiram o confronto das suas características atuais com aquelas projetadas para o término da sua vida útil. Estudos para constatar eventuais minimizações da EPU e controle da resistência mecânica de corpos cerâmicos de vedação foram desenvolvidos com o emprego das massas das Cerâmicas ditas "A" e "B", as quais foram manipuladas de forma idêntica. Os teores diferenciados da incorporação feita a cada uma das citadas massas dos carbonatos empregados, a saber, os carbonatos de cálcio e de magnésio, foram calculados com o propósito de gerarem idênticos teores de óxidos após o desprendimento do dióxido de carbono ao longo do ciclo da queima. Os resultados obtidos evidenciaram, para os blocos obtidos ao longo de ciclo de queima entre 850-1000°C, uma redução universal da EPU decorrente da ação do carbonato de cálcio, e uma discreta tendência da sua redução decorrente da adição do carbonato de magnésio; tais reduções de EPU se deveram à formação de fases cristalinas desencadeadas pela ação dos referidos carbonatos. O maior valor de perda de massa, o surgimento da brucita, e os elevados valores de absorção de água decorrentes das adições magnesianas justificaram as menores reduções, ou ausência de reduções, de EPUs delas decorrentes. Quando as duas citadas massas foram manipuladas sem adições, aquela com maior teor de argila apresentou valores mais elevados de EPU, o que se explica, já que a maior quantidade de argila forma maior quantidade de fase vítrea. As adições utilizadas intervieram não só na EPU como também nas propriedades cerâmicas dos corpos-de-prova analisados. As adições calcárias e magnesianas, de forma quase absoluta, tenderem ao aumento das absorções de água, e, quanto à interferência no aumento da resistência mecânica, marcante foi a grande suscetibilidade ao teor "médio" (16,3%) de adição magnesiana associado à temperatura de queima de 1000°C, situação em que a tensão de ruptura à flexão, tanto para a Cerâmica "A" quanto para a Cerâmica "B", apresentou valores desproporcionalmente superiores àqueles relativos a temperaturas de queima inferiores a 1000°C, fato provavelmente devido à efetiva presença da enstatita e da ringwoodita a esta temperatura de queima.
The use of ceramic blocks in structural masonry since the last thirty years has demanded their capacity of absorbing mechanic efforts resulting from the own weight of building and respective overloads. Researches intended to make possible the new performance of ceramic blocks have not been intensive enough to definitively assure a good structural performance, and some problems concerning their mechanic properties and moisture expansion have shown the need of deeply improve their characteristics. Aiming at that purpose, this doctoral thesis has developed some investigations to identify new patterns that may contribute to increase the knowledge of moisture expansion and mechanic properties of ceramic blocks. To achieve that purpose, we started from information provided by technical literature concerning the good effects of calcium oxide and magnesium oxide incorporated to the rawmaterials of ceramic blocks. Results obtained from the autoclaved specimens have shown the differences between their present characteristics and those expected to be at the end of their working life. Researches to confirm possible moisture expansion minimizations and control of mechanic resistance of packing ceramic bodies have been carried out by using ceramic masses called "A" and "B", handled alike. Different contents of the carbonate used, such as calcium and magnesium carbonates, have been estimated, with the purpose of providing the same oxide contents after the carbon dioxide exit, along the firing cycle. Blocks obtained during a firing cycle between 850-1000°C show a universal moisture expansion decrease resulting from the action of calcium carbonate and a strong trend of its decrease resulting from the addition of magnesium carbonate. Such moisture expansion decreases resulted from the crystalline stages developed by the activity of those carbonates. The highest rate of mass loss, ocurrence of brucite and high rates of water absorption resulting from the addition of magnesium carbonate justify shorter decreases or even non-reduction or moisture expansion resulting therefrom. When both masses were handled without additions, the one with higher rate of clay showed higher moisture expansion values, since a higher rate of clay responsible for higher quantity of vitreous phases. Added material interfered both in moisture expansion and in the ceramic properties of observed specimens. Remarkable was the high susceptibility of the medium content (16.3%) of magnesium carbonate addition interfering in the increase of mechanical resistance, joined to the firing temperature at 1000°C, and acording to this tendency, rupture tension, in both Ceramics "A" and "B", showed disproportionably higher figures relative to firing temperatures under 1000°C. This fact is probably due to the effective presence of enstatite and ringwoodite at this firing temperature.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
This study concentrates on the use of micro particles of limestone (CMV) and nano scale calcium carbonate (Np-CaCO3) in Portland cement (OPC) substitution in order to evaluate the influence in hydration reactions, microstructural morphology, mechanical properties and the durability of cement pastes and mortar. Specimens where characterized by X-ray diffraction, scanning electron microscopy, uniaxial compression, micro hardness and thermo gravimetric analysis. Atypical morphologies of calcium silicate hydrate (C-S-H) were observed in the pastes in the presence of high amount of Np-CaCO3. The results indicate that the Np-CaCO3 is reactive; accelerating early age C-S-H formation. Based on the morphological and mechanical properties, a synergetic effect was observed by the combined addition of CMV with low amounts of Np-CaCO3. Compressive strength results of the mortars are compatible with the standard requisite of the American Society of Testing Materials (ASTM). The durability of the mortars was evaluated by expositional aging methods in natural and laboratory environment for 6 months. The mechanical properties and durability of the composite cement mortars are competitive with results obtained by the reference mortars. By overall analysis of the results, it was concluded that OPC substitution of 10-30 wt.% CMV, when combined with controlled amount of Np-CaCO3 prove viable.
A presente pesquisa se concentra no uso de calcário mineral micrométrico (CMV) e nanopartículas de carbonato de cálcio (Np-CaCO3) na substituição de cimento Portland (OPC), visando avaliar a influência nas reações de hidratação, morfologia, microestrutura, propriedades mecânicas e durabilidade de pastas e argamassas de cimento. Os corpos de prova foram caracterizados por difração de raios X, microscopia eletrônica de varredura, ensaios de compressão, microdureza e análise termogravimétrica. Nas pastas foram observadas morfologias atípicas de silicato de cálcio hidratado (C-S-H) na presença de altos teores de Np-CaCO3. Os resultados indicam que as Np-CaCO3 atuam como reativos acelerando a formação do C-S-H nas primeiras idades. Em base das propriedades morfológicas e mecânicas, foi observado um efeito sinérgico quando combinados baixos teores Np-CaCO3 com CMV. Os valores de resistência a compressão das argamassas são compatíveis com os valores padrão das normas da Sociedade Americana de Testes e Materiais (ASTM). As argamassas envelhecidas em ambiente natural e laboratório por até 6 meses de exposição mostraram propriedades mecânicas e durabilidade comparáveis com resultados obtidos para argamassas feitas com cimentos de referência. Foi viável a substituição de OPC, mesmo para altos teores de carbonatos (10-35%), em especial quando combinados com teores controlados de Np-CaCO3.

A corrosão de armaduras é uma das causas mais comuns de degradação mecânica em estruturas em concreto armado. Esse processo leva à redução da vida útil e, consequentemente, a prejuízos econômicos. Desse modo, o presente trabalho visa contribuir com a análise dos fenômenos associados à degradação mecânica do concreto armado sujeito a processos corrosivos devido à carbonatação e à ação de cloretos. Para tal finalidade, modelos analíticos baseados na segunda lei de Fick são usados para quantificar a difusão de CO2 e de íons cloreto no concreto, os quais permitem determinar o tempo de início da corrosão. A degradação mecânica de estruturas em concreto armado é considerada por meio de um modelo em dano concentrado que contempla perda da rigidez, redução da área de aço e da tensão de escoamento de armaduras devido ao processo corrosivo. A formulação de dano concentrado foi modificada de forma a incluir uma variável de estado de corrosão e uma lei de evolução da corrosão, baseada em equações semi-empíricas disponíveis na literatura. Essas equações determinam a redução no diâmetro das armaduras e a perda da capacidade resistente do aço. O problema da corrosão é formulado como um processo estocástico sendo resolvido por meio do método de simulação de Monte Carlo para dois exemplos: uma viga isostática e um pórtico plano com grau de hiperestaticidade igual a três. A formulação da equação de estado limite é baseada em um valor de dano aceitável. Curvas de probabilidade de início da corrosão e de probabilidade de falha da estrutura são obtidas ao longo de 50 anos. No caso da estrutura hiperestática, o caminho mais provável de falha, também chamado de caminho crítico, é determinado. Observa-se que o processo corrosivo provoca mudanças no caminho crítico, e portanto, deve ser considerado nas análises de reparo estrutural. Mapas de dano e de probabilidade de falha foram desenvolvidos para mostrar as mudanças no comportamento estrutural devido à corrosão.
The reinforcement\'s corrosion is one of the most common causes of mechanical degradation in reinforced concrete structures. This process leads to the reduction of the service life and, consequently, economic loss. Thereby, this study aims to contribute with the analysis of the phenomena associated to the mechanical degradation of reinforced concrete, due to the carbonation and the chloride ions. For this purpose, analytical models based on second Fick\'s law are used to quantify CO2 and chloride ions diffusion, which enables to determine the corrosion time initiation. The mechanical degradation of reinforced concrete structures is modeles by the lumped damage model which accounts for stiffness loss, reinforcement mass loss and yield stress reduction due to the corrosive process. The lumped damage formulation was modified to include the state corrosion variable and the corrosion evolution law based on semi-empirical equations available in the literature. These equations determine the reinforcement\'s diameter reduction and the loss of resistant capacity of the reinforcement\'s bar. The corrosion problem is formulated as a stochastic process and solved by the Monte Carlo simulation for two examples: an isostatic beam and a hyperstatic frame. The limit state functions are based on the acceptable damage value. Curves of probability of corrosion initiation and probability of failure are obtained over a range of 50 years. In the hyperstatic case, the most probable failure path, also named the critical path, is determined. It is observed that the corrosive process causes changes on the critical path and, therefore, it must be accounted on structural repair analysis. Damage and probability of failure maps were developed to show the changes on the structural behavior due to the corrosion.

碩士
國立臺灣科技大學
營建工程系
99
ABSTRACT The purpose of this study is to explore the effects of humidity on the carbonation of the reinforced concrete and its associated mechanical properties and corrosion resistance. Concrete specimens with w/c of 0.6 were cured in saturated lime water for 28 days, oven-dried, and then put in accelerated environments with a constant temperature of 25 °C, CO2 concentration of 50% by volume, and various humidity environments, including constant humidities of 50%, 70%, and 90%, and cycling relative humidities ranging from 50% to 90%, or 70% to 90%. Results were summarized as follows. First, the cycling humidities induced higher carbonation coefficient than the constant humidity. Second, the converted carbonation coefficients determined by the cycling humidity environment were close to those determined from the onsite investigation. Third, the mechanical properties of the concrete were found increased by the carbonation. Fourth, the carbonation reduced the corrosion resistances of the reinforcements. Both the changes in the mechanical properties of the concrete and corrosion resistances of the reinforcements were associated with carbonation depth more than the relative humidities of the accelerated environment.

abstract: Increased priority on the minimization of environmental impacts of conventional construction materials in recent years has motivated increased use of waste materials or bi-products such as fly ash, blast furnace slag with a view to reduce or eliminate the manufacturing/consumption of ordinary portland cement (OPC) which accounts for approximately 5-7% of global carbon dioxide emission. The current study explores, for the first time, the possibility of carbonating waste metallic iron powder to develop carbon-negative sustainable binder systems for concrete. The fundamental premise of this work is that metallic iron will react with aqueous CO2 under controlled conditions to form complex iron carbonates which have binding capabilities. The compressive and flexural strengths of the chosen iron-based binder systems increase with carbonation duration and the specimens carbonated for 4 days exhibit mechanical properties that are comparable to those of companion ordinary portland cement systems. The optimal mixture proportion and carbonation regime for this non-conventional sustainable binder is established based on the study of carbonation efficiency of a series of mixtures using thermogravimetric analysis. The pore- and micro-structural features of this novel binding material are also evaluated. The fracture response of this novel binder is evaluated using strain energy release rate and measurement of fracture process zone using digital image correlation (DIC). The iron-based binder system exhibits significantly higher strain energy release rates when compared to those of the OPC systems in both the unreinforced and glass fiber reinforced states. The iron-based binder also exhibits higher amount of area of fracture process zone due to its ability to undergo inelastic deformation facilitated by unreacted metallic iron particle inclusions in the microstructure that helps crack bridging /deflection. The intrinsic nano-mechanical properties of carbonate reaction product are explored using statistical nanoindentation technique coupled with a stochastic deconvolution algorithm. Effect of exposure to high temperature (up to 800°C) is also studied. Iron-based binder shows significantly higher residual flexural strength after exposure to high temperatures. Results of this comprehensive study establish the viability of this binder type for concrete as an environment-friendly and economical alternative to OPC.
Dissertation/Thesis
Doctoral Dissertation Civil and Environmental Engineering 2015

Non-stoichiometric strontium iron oxide is described by an abbreviated formula SrFeOx (2.5 ≤ x ≤ 3.0) exhibits a variety of interesting physical and chemical properties over a broad range of temperatures and in different gaseous environments. The oxide contains a mixture of iron in the trivalent and the rare tetravalent state. The material at elevated temperature is a mixed oxygen conductor and it, or its derivatives,can have practical applications in oxygen conducting devices such as pressure driven oxygen generators, partial oxidation reactors in electrodes for solid oxide fuel cells (SOFC). ¶ This thesis examines the behaviour of the material at ambient and elevated temperatures using a broad spectrum of solid state experimental techniques such as: x-ray and neutron powder diffraction,thermogravimetric and calorimetric methods,scanning electron microscopy and Mossbauer spectroscopy. Changes in the oxide were induced using conventional thermal treatment in various atmospheres as well as mechanical energy (ball milling). ¶ ...