Cement is the construction building material with higher responsibility by carbon dioxide emission of all industrial human activities, besides be a considerably expensive material, more than the rice husk ash in nature. Environmental benefits are generated in its utilization, because rice husk ashes are industrial process residues of the grain processing, that are discarded in the environment without none care. The using of these ashes in partial cement substitution in structural concrete, beside of the economical and environmental benefits, proportionate, in general, a higher useful life to the reinforced concrete structures. Based in theses environmental principles, this work aims at to study the technical and economical viability of the RHA utilization, substituting the cement partially, in concrete mixtures for conventional concrete. concrete prototypes with 20 x 20 x 70 cm, with and without ground and non-ground RHA, in 0%, 15% and 25% contents of cement substitution, with water/binder ratios of 0,45, 0,55 and 0,65. Exposed in natural environmental conditions (0,3 0,4% of CO2) the concrete prototypes were analyzed at 18, 24 and 30 months, to the axial compressive strength and carbonation by means of extraction of specimens perpendicularly cut to the casting direction, with 10 x 20 cm dimensions. The axial compressive strength at 18 months of the ground RHA mixtures were higher to the reference concrete, while the natural RHA ones were lower than the latter, with higher decreases for the 25% content than for 15%. The natural carbonation coefficients of reference concrete were the smallest ones, followed by the ground RHA with 15% and 25% and, after, with natural RHA, 15% and 25%. The results show that is possible substitute until 15% of cement by natural rice husk ash without pronounced strength losses (around 20%) and with carbonation coefficients between 4 and 5 mm.ano-0,5, values considered adjusted for conventional concrete. / O cimento é o material de construção com maior responsabilidade pela emissão do dióxido de carbono de todas as atividades industriais humanas, alem de ser um material consideravelmente mais caro do que as CCA s, in natura. Benefícios ambientais são gerados na sua utilização, pois as cinzas de casca de arroz são resíduos de processos industriais do beneficiamento do grão, que muitas vezes são descartados no meio ambiente, sem nenhuma preocupação ambiental. Usá-las em substituição parcial do cimento em concretos estruturais, além de benefícios econômicos e ambientais, proporciona, geralmente, uma maior vida útil às estruturas de concreto armado. Baseado nestes preceitos ambientais, esta pesquisa tem por objetivo o estudo da viabilidade técnica e econômica da utilização da cinza de casca de arroz (CCA), substituindo parcialmente o cimento nas misturas de concretos para uso em concreto convencional. Foram moldados protótipos de concreto de 20 x 20 x 70 cm, com CCA natural e moída, nos teores de 0, 15 e 25%, em substituição ao cimento, nas relações água/aglomerante 0,45, 0,55 e 0,65. Expostos em condições ambientais naturais (0,3 0,4% de dióxido de carbono), os protótipos de concreto foram analisados nas idades de 18, 24 e 30 meses, quanto à resistência, compressão axial e frente ao fenômeno de carbonatação natural, por meio da extração de testemunhos cortados perpendiculares à direção de moldagem, com dimensões 10 x 20 cm. A resistência à compressão axial a 18 meses dos traços com CCA moída foram superiores ao concreto de referência, enquanto que os de cinza natural foram menores do que as misturas com CCA moída, com quedas maiores para o teor de 25% do que para 15%. Os coeficientes de carbonatação natural do traço referência foram os menores de todos, seguidos dos CCA moída, com 15 e 25% e, após, com a CCA natural, de 15% e 25%. Os resultados mostram que é possível substituir até 15% de cimento por cinza de casca de arroz natural, sem moagem, sem perdas acentuadas de resistência (ao redor de 20%) e com coeficientes de carbonatação entre 4 e 5 mm.ano-0,5, valores que podem ser considerados adequados para concreto convencional.

This study investigates the mechanical differences between old and newly produced slatted floors through a four-point bending test. To understand to what extent the actual environment has affected the slatted floors, the carbonation depth and corrosion will be examined. The tests showed no mechanical differences between slatted floors which had been in service for a certain amount of years and newly produces ones. Corrosion could be observed on some of the samples but it was not because of the carbonation process. When comparing the calculations of reinforced and pre-stressed concrete slatted floors, the result showed that the pre-stressed floor could carry up to double the load of what the reinforced slatted floor could. The conclusion of this study is, that the pre-stressed slatted floors will certainly hold for at least thirty years and will most likely hold for many years to come.

This thesis investigates sustainability measures for quicklime and cement clinker production. It is the aim of this thesis to contribute to the effort of creating a more sustainable modus of industrial production. The methods used comprises process simulations through multicomponent chemical equilibrium calculations, fuel characterization and raw materials characterization through dynamic rate thermogravimetry. The investigated measures relate to alternative fuels, co-combustion, oxygen enrichment, oxyfuel combustion, mineral carbonation and optimizing raw material mixes based on thermal decomposition characteristics. The predictive multicomponent chemical equilibrium simulation tool developed has been used to investigate new process designs and combustion concepts. The results show that fuel selection and oxygen enrichment influence energy efficiency, and that oxyfuel combustion and mineral carbonation could allow for considerable emission reductions at low energy penalty, as compared to conventional post-combustion carbon dioxide capture technologies. Dynamic rate thermogravimetry, applied to kiln feed limestone, allows for improved feed analysis with a deeper understanding of how mixing of different feed materials will affect the production processes. The predictive simulation tool has proven to be of practical value when planning and executing production and full scale campaigns, reducing costs related to trial and error. The main conclusion of this work is that several measures are available to increase the sustainability of the industry.

A reactive transport model is proposed to simulate the reactivity of cement based material in contact with CO2-saturated brine and supercritical CO2 (scCO2) under CO2 geological storage conditions. This code is developed to solve simultaneously transport and chemistry by a global coupled approach, considering the effect of temperature and pressure. The variability of scCO2 properties with pressure and temperature, such as solubility in water, density and viscosity are taken into account. It is assumed that all chemical processes are in thermodynamical equilibrium. Dissolution and precipitation reactions for portlandite (CH) and calcite (CC) are described by mass action laws and threshold of ion activity products in order to account for complete dissolved minerals. A chemical kinetics for the dissolution and precipitation of CH and CC is introduced to facilitate numerical convergence. One properly chosen variable is able to capture the precipitation and dissolution of the relevant phase. A generalization of the mass action law is developed and applied to calcium silicate hydrates (C-S-H) to take into account the continuous variation (decrease) of the Ca/Si ratio during the dissolution reaction of C-S-H. The changes in porosity and microstructure induced by the precipitation and dissolution reactions are also taken into account. Couplings between transport equations and chemical reactions are treated thanks to five mass balance equations written for each atom (Ca, Si, C, K, Cl) as well as one equation for charge balance and one for the total mass. Ion transport is described by using the Nernst-Plank equation as well as advection, while gas and liquid mass flows are governed by advection. Effect of the microstructure and saturation change during carbonation to transport properties is also considered. The model is implemented within a finite-volume code, Bil. Principles of this method and modeling approach are discussed and illustrated with the help of a simple example. This model, with all the efforts above, is able to simulate the carbonation processes for cement based materials, at both saturated and unsaturated conditions, in a wide CO2 concentration, temperature and pressure range. Several sets of experiments, including sandstone-like conditions, limestone-like conditions, supercritical CO2 boundary and unsaturated conditions reported in the literature are simulated. Good predictions are provided by the code when compared with experimental observations. Some experimental observed phenomena are also explained by the model in terms of calcite precipitation front, CH dissolution front, porosity profile, etc

Un modèle de transport réactif est proposé pour simuler la réactivité des matériaux à base de ciment en contact avec une saumure saturée en CO2 et/ou le CO2 supercritique (CO2sc) dans les conditions de stockage géologique du CO2. Un code a été développé pour résoudre simultanément le transport et la chimie par une approche globale couplée, compte tenu de l'effet de la température et de la pression. La variabilité des propriétés du CO2sc avec la pression et la température, telles que la solubilité dans l'eau, la densité et la viscosité sont pris en compte. On suppose que tous les processus chimiques sont en équilibre thermodynamique. Les réactions de dissolution et de précipitation de la portlandite (CH) et de calcite (CC) sont décrites par des lois d'action de masse et des seuils de produit d'activité ioniques. Une cinétique de dissolution de CH est introduite pour faciliter la convergence numérique. La définition d'une variable principale permet de capturer la précipitation et la dissolution des phases solides à base de calcium. Une généralisation de la loi d'action de masse est développée et appliquée aux silicates de calcium hydratés (CSH) pour tenir compte de la variation continue (diminution) du rapport Ca/Si au cours de la dissolution des CSH. Les variations de porosité et de la microstructure induites par les réactions de précipitation et de dissolution sont également prises en compte. Le couplage entre le transport et la chimie est modélisé par cinq équations de bilan de masse écrites pour chaque atome (Ca, Si, C, K, Cl), ainsi que par une équation de conservation de la masse totale et celle de la charge électrique. Les lois de Darcy et de Nernst-Planck sont utilisées pour décrire le transport de masse et d'ions. Les propriétés de transport dépendent du degré de saturation et de la porosité. Le modèle est implémenté dans le code de volumes finis, Bil. Les principes de cette méthode et l'approche de modélisation sont discutés et illustrés sur un exemple simple. Ce modèle est en mesure de simuler les processus de carbonatation des matériaux à base de ciment, dans des conditions à la fois saturés et insaturés, dans une large plage de concentration de CO2, de température et de pression. Plusieurs expériences, rapportées dans la littérature, sont simulées en utilisant divers types de conditions aux limites: (i) solutions saturées ou non en CO2 et carbonate de calcium, (ii) gas supercritique de CO2. Les prédictions sont comparées avec les observations expérimentales. Certains phénomènes observés expérimentalement peuvent être également expliqués par le modèle / A reactive transport model is proposed to simulate the reactivity of cement based material in contact with CO2-saturated brine and supercritical CO2 (scCO2) under CO2 geological storage conditions. This code is developed to solve simultaneously transport and chemistry by a global coupled approach, considering the effect of temperature and pressure. The variability of scCO2 properties with pressure and temperature, such as solubility in water, density and viscosity are taken into account. It is assumed that all chemical processes are in thermodynamical equilibrium. Dissolution and precipitation reactions for portlandite (CH) and calcite (CC) are described by mass action laws and threshold of ion activity products in order to account for complete dissolved minerals. A chemical kinetics for the dissolution and precipitation of CH and CC is introduced to facilitate numerical convergence. One properly chosen variable is able to capture the precipitation and dissolution of the relevant phase. A generalization of the mass action law is developed and applied to calcium silicate hydrates (C-S-H) to take into account the continuous variation (decrease) of the Ca/Si ratio during the dissolution reaction of C-S-H. The changes in porosity and microstructure induced by the precipitation and dissolution reactions are also taken into account. Couplings between transport equations and chemical reactions are treated thanks to five mass balance equations written for each atom (Ca, Si, C, K, Cl) as well as one equation for charge balance and one for the total mass. Ion transport is described by using the Nernst-Plank equation as well as advection, while gas and liquid mass flows are governed by advection. Effect of the microstructure and saturation change during carbonation to transport properties is also considered. The model is implemented within a finite-volume code, Bil. Principles of this method and modeling approach are discussed and illustrated with the help of a simple example. This model, with all the efforts above, is able to simulate the carbonation processes for cement based materials, at both saturated and unsaturated conditions, in a wide CO2 concentration, temperature and pressure range. Several sets of experiments, including sandstone-like conditions, limestone-like conditions, supercritical CO2 boundary and unsaturated conditions reported in the literature are simulated. Good predictions are provided by the code when compared with experimental observations. Some experimental observed phenomena are also explained by the model in terms of calcite precipitation front, CH dissolution front, porosity profile, etc

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology / Several technologies are currently being developed to mitigate the greenhouse gas CO2. One of these promising processes is industrial mineral carbonation whereby alkaline industrial wastes are taken as raw material. The process is a multi-step process which involves the extraction of calcium from industrial alkaline wastes and the subsequent reaction of extracted calcium rich supernatant with CO2 at elevated pH to form stable carbonates. Steelmaking slags were selected from four different plants in SA and used for this investigation owing this to their high calcium content. The potentially-suitable four slags were selected on the basis of their Ca content and high chemical reactivity. The objective of this investigation was to develop a common leach process for all four steel slags to achieve a complete Ca extraction from slags. A Ca rich solution was carbonated to achieve a stable carbonate that can be used. Experiments were carried out using ammonium reagents and a hydroxide reagent to investigate their suitability for the rapid, selective extraction of calcium. Calcium was leached under different experimental conditions including varying leachant concentrations, temperatures and solid to liquid ratios. The slags exhibited contrasting reactive properties to different leachants, which can essentially be explained in terms of differences in mineralogical composition, hence mineral solubility characteristics. Leaching with 2M NH4NO3 aqueous solution at room temperature extraction efficiency increased with increasing concentration. The extent of extraction was different for the four slags. WMO5 showed a complete dissolution of Ca within 20 min of experiment. This difference is due to their different Ca-containing minerals. Same is observed with aqueous NH4CL but WMO5 did not reach a complete dissolution as with NH4NO3. Aqueous NaOH made it impossible for Ca extraction due to its high pH and upon slag addition it was more elevated. Increasing solid to liquid ratio had an influence in percentage slag loss. The pH of leach solution was elevated to 9 making it difficult to extract Ca. Under controlled conditions (pH kept under 1) optimal slag dissolution was achieved with traces of larnite and large amount of brownmillerite. The generated Ca-rich leachate was carbonated in a 600 ml reactor vessel with liquid CO2. A stable carbonate aggregate was produced. / Council for Geoscience Vaal University of Technology

L’objectif de cette thèse sous contrat cifre entre la société S3d et l’Ecole des Mines de Nantes a été de développer une solution innovante et rentable de production de bio-GNV (Gaz Naturel pour Véhicules) à l’échelle d’une exploitation agricole. Les solutions testées pour capter le CO2 et l’H2S se sont respectivement basées sur les réactions de carbonatation accélérée et la sulfuration du fer sur matériaux alcalins. Pour cela, un co-produits industriels à faible valeur ajoutée a été identifié : les laitiers sidérurgiques issus de four de conversion à oxygène (laitiers BOF pour Basic Oxygen Furnace). Des essais ont été menés à l’échelle du laboratoire sur le CO2 etl’H2S en réacteurs statiques puis en colonne dynamique. L’étude de la carbonatation accélérée du CO2 sur les laitiers BOF et la chaux a permis d’estimer les capacités de capture du CO2 à 49 gCO2/kgBOF pour les BOF contre 265,4 gCO2/kg chaux pour la chaux. La sulfuration des laitiers par H2S a conduit à une capacité de capture de 7,0 ± 1,0 gH2S/kgBOF. Suite à ces résultats, la faisabilité technique a été évaluée sur un biogaz réel produit sur une exploitation agricole vendéenne. Des tests sur site dans une colonne garnie de 200 g de laitiers en lit fixe pendant 46 jours ont permis de valider la faisabilité de la désulfurisation parles laitiers BOF en conditions réelles. Cependant, les réflexions menées sur la carbonatation du CO2 ont conduit à l’introduction d’une solution alternative à savoir la filtration membranaire. Enfin, le bilan économique sur la filière complète a montré que la rentabilité de cette unité était contrainte par un investissement de 75 000 € subventionné à 30% et la consommation d’au moins 6 pleins/semaine. / Bio-NGV (bio- Natural Gas for Vehicles) is a bio-fuel based on the biogas in which components such as CO2and H2S are removed. But the economical feasibility of available and commercial technologies to perform these removals is limited to 80 Nm3/h of treated biogas. Regarding farm scale biogas plant, fuel needs of 1 fill-upper day would represent the treatment of only 1 Nm3/hof raw biogas. The aim of our work was to develop a solution economically adapted to farm scale to produce bio-NGV from biogas. An alternative and low cost material, BOF slag (Basic Oxygen Furnace slag), was then identified to perform CO2 removal by accelerated carbonation and H2S removal by iron sulfidation. The accelerated carbonation feasibility was evaluated in batch and dynamic reactors under laboratory conditions. But, removal capacities obtained were insufficient to be used under real conditions. Lime was then tested and CO2 removal capacities observed were higher than BOFslag ones but still insufficient. Iron sulfidation by H2Swas also tested under laboratory conditions. Batch reactor and dynamic column investigations led to an interesting H2S removal capacity of 7,0 ± 1,0 gH2S/kgBOF. Based on this result, performances were also validated under real conditions on the biogas produced on site field. According to the whole experimental data, the complete process of bio-NGV production was designed including the H2S removal performed by BOF slag, CO2 removal achieved in two membranes and the 200 bars compression. Finally, the overall economical balance has showed that a total investment of 75 000 € with a subsidy rates of 30% and a weekly fuel consumption between 6 and 28 fill-up/week will lead to a profitable project.

O regolito é o manto do intemperismo existente sobre as rochas. Este manto pode ser constituído estruturalmente por três entidades distintas denominadas, solo, sedimento e saprolito. Ambas são produtos da intemperização das rochas. No entanto, o saprolito é definido como o único produto não transportado da intemperização isovolumétrica do litotipo originário. Diferente dos solos, dos sedimentos ou das rochas, não existe uma ciência específica para o estudo dos saprolitos. A saprolitologia não existe oficialmente, porém, pode ser implicitamente encontrada em trabalhos científicos de todo o mundo. No primeiro capítulo da tese, apresenta-se o estado da arte dos estudos dos saprolitos e sugere-se a consolidação da saprolitologia com o intuito de incentivar o incremento das pesquisas voltadas a esta entidade ainda pouco conhecida. De fato, os processos relacionados à intemperização isovolumétrica das rochas ainda não foram completamente compreendidos. Neste contexto, o Estado de Pernambuco, no nordeste do Brasil, apresenta condições geomorfológicas e climáticas propícias ao estudo da formação de saprolitos. No segundo capítulo da tese, demonstra-se que o intemperismo isovolumétrico de treze rochas cristalinas foi mais influenciado pelas condições microambientais, a exemplo da dinâmica da água através da microestrutura, do que pelas condições macroambientais. Posteriormente ao intemperismo isovolumétrico, diferenças morfológicas e geoquímicas ocorrem durante a evolução vertical do regolito. Entretanto, os domínios da saprolitogênese e da pedogênese são difíceis de diferenciar. No terceiro capítulo da tese, avaliou-se a evolução morfológica, estrutural e geoquímica de treze perfis formados por sistemas solo-saprolitos derivados do embasamento cristalino do Estado de Pernambuco. Anomalias nos índices de mensuração do intemperismo demonstram que o aumento gradual do grau de intemperização dos horizontes mais superficiais em relação aos horizontes inferiores não é a regra durante a evolução vertical do regolito. Em adição, a geoquímica e a morfologia dos perfis estudados indicam que alguns sistemas solo-saprolitos desenvolveram-se de forma interligada e outros apresentam evidências de que a formação do saprolito pode ter ocorrido após a formação do solo sobrejacente. Durante a evolução do regolito, o solo e o saprolito influenciam processos essenciais ao meio ambiente. No quarto capítulo da tese, descrevem-se as implicações agrícolas e ambientais dos treze perfis descritos no terceiro capítulo. Os resultados sugerem que os processos geoquímicos existentes nos sistemas solo-saprolitos, a exemplo da \"mineral carbonation\", influenciam o fluxo de elementos através do ecossistema circundante e demonstram que os saprolitos possuem importância agrícola e ambiental análoga à dos solos, influenciando processos de relevância agroambientais tais como a dinâmica da água, a retenção e transporte de nutrientes e/ou a retenção e transporte de contaminantes ou poluentes. / The regolith is the mantle of weathering above the rocks. This mantle may consist of three structurally distinct entities denominated sediment, soil and saprolite. All are products of rock weathering. Saprolite is defined as the product of in situ, isovolumetric weathering of the lithotype. Unlike the soils, sediments or rocks, there is no specific science dedicated to the study of saprolite. The saprolihtology does not exist formally. However, it can implicitly be found in scientific papers from around the world. The first chapter of the thesis presents the state of the art of saprolite studies and suggests the consolidation of saprolithology in order to encourage the development of research focused in this entity poorly known. In fact, the processes related to the isovolumetric weathering of rocks are not yet fully understood. In this context, the Pernambuco State in Northeastern Brazil have geomorphological and climatic conditions prone to the study of the saprolite formation and evolution. The second chapter of this thesis demonstrates that the isovolumetric weathering of the thirteen crystalline rocks was more influenced by microenvironmental conditions, such as the water dynamics through the microstructure, than the macro-environmental conditions. Subsequent to isovolumetric weathering, morphological and geochemical differenciation occur during the vertical evolution of regolith. However, it is difficult to differentiate the domains of saprolithogenesis and pedogenesis. The third chapter of the thesis reports the morphological, structural and geochemical evolution of the thirteen profiles formed by soil-saprolite systems derived from the crystalline basement of the Pernambuco State. Anomalies in the weathering measurement indexes showed that the gradual increase in the degree of weathering from the surface horizons towards the subsurface horizons is not the rule for the vertical development of regolito. In addition, the geochemistry and the morphology of the studied profiles indicate that some soil-saprolite systems evolved in an interconnected way and others provide evidence that the formation of saprolite may have occurred after the formation of the overlying soil. During the regolith evolution, soil and saprolite influence key environmental processes. The fourth chapter describes the agricultural and environmental implications of the processes acting in the thirteen profiles described in the third chapter. The results suggest that existing processes in geochemical soil-saprolite systems, such as the mineral carbonation, have influenced the elements flow through the surrounding ecosystem and demonstrate that saprolites have agricultural and environmental importance analogous to soil, influencing processes such as water fluxes, retention and transport of nutrients and/or of contaminants or pollutants.

A lower-alkalinity cement based on MgO and SiO2 blends is analysed to develop clinker-free Fibre Reinforced Cementitious Composites (FRCC) with cellulosic fibres in order to solve the durability problems of this type of fibres when used in FRCC with Portland cement. Hydration evolution from 7 to 28 days of different MgO-SiO2 formulations is assessed. The main hydration products are Mg(OH)2 and M-S-H gels for all the formulations studied regardless of age. Hardened pastes are obtained with pH values < 11 and good mechanical properties compared to conventional Portland cement. 60% MgO-40% SiO2 system is chosen as optimal for the development FRCC since is the most mechanical resistant and is less alkaline compared with 70% MgO-30% SiO2. FRCC based on magnesium oxide and silica (MgO-SiO2) cement with cellulose fibres are produced to study the durability of lignocellulosic fibres in a lower pH environment than the ordinary Portland cement (PC). Flexural performance and physical tests (apparent porosity, bulk density and water absorption) of samples at 28 days and after 200 accelerated ageing cycles (aac) are compared. Two types of vegetable fibres are utilised: eucalyptus and pine pulps. MgO-SiO2 cement preserves cellulosic fibres integrity after ageing, so composites made out of MgO-SiO2 exhibit significant higher performance after 200 cycles of accelerated ageing than Portland cement composites. High CO2 concentration environment is evaluated as a curing treatment in order to optimise MgO- SiO2 matrices in FRCC. Samples are cured under two different conditions: 1) steam water curing at 55°C and 2) a complementary high CO2 concentration (20% by volume). In carbonated samples, Mg(OH)2 content is clearly lowered while new crystals of hydromagnesite [Mg5 (CO3)4⋅(OH) 2⋅4H2O] are produced. After carbonation, M-S-H gel content is also reduced, suggesting that this phase is also carbonated. Carbonation affects positively to the composite mechanical strength and physical properties with no deleterious effects after ageing since it increases matrix rigidity. The addition of sepiolite in FRCC is studied as a possible additive constituent of the binding matrix. Small cement replacement (1 and 2% wt.) by sepiolite is introduced and studied in hardened cement pastes and, later, in FRCC systems. When used only in cement pastes, it improves Dynamic Modulus of Elasticity over time. Bending tests prove the outcome of this additive on the mechanical performance of the composite: it improves composite homogeneity. Ageing effects are reported after embedding sisal fibres in MgO-SiO2 and PC systems and submitting them to different ageing conditions. This comparative study of fibre degradation applied in different cementitious matrices reveals the real compatibility of lignocellulosic fibres and Mg-based cements. Sisal fibres, even after accelerated ageing, do neither suffer a significant reduction in cellulose content nor in cellulose crystallinity and crystallite size, when exposed to MgO-SiO2 cement. Fibre integrity is preserved and no deposition of cement phases is produced in MgO-SiO2 environment. / Um cimento de baixa alcalinidade à base de blendas de MgO e SiO2 é analisado para o desenvolvimento de Compósitos Cimentícios Reforçados com Fibras (CCRF) celulósicas sem clínquer para resolver os problemas de durabilidade de este tipo de fibras quando são usadas em CCRF com cimento Portland. A evolução da hidratação, desde 7 aos 28 dias, das diferentes formulações é avaliada. Os principais produtos hidratados são o Mg(OH)2 e o gel M-S-H para todas as formulações independentemente da idade estudada. As pastas endurecidas apresentam valores de pH < 11 e bom desempenho mecânico comparado com o cimento Portland convencional. O sistema 60% MgO-40% SiO2 é escolhido como a formulação ótima para o desenvolvimento de CCRF já que é a mais resistente e menos alcalina comparada com 70% MgO-30% SiO2. CCRF com cimento à base de óxido de magnésio e sílica (MgO-SiO2) e fibras celulósicas são produzidos para a análise da durabilidade das fibras lignocelulósicas em ambientes com valores de pH mais baixos comparados com o cimento Portland (PC). O desempenho mecânico a flexão e os ensaios físicos (porosidade aparente, densidade aparente e absorção de água) são comparados aos 28 dias e após de 200 ciclos de envelhecimento acelerado. O cimento à base de MgO-SiO2 preserva a integridade das fibras após o envelhecimento. Os compósitos produzidos com este cimento exibem melhores propriedades após 200 ciclos de envelhecimento acelerado que os compósitos produzidos com cimento Portland. Ambientes com alta concentração de CO2 são avaliados como tratamento de cura para otimizar as matrizes MgO- SiO2 nos CCRF. As amostras são curadas sob 2 condições diferençadas: 1) cura com vapor de água a 55oC e 2) cura com alta concentração de CO2 (20% do volume). As amostras carbonatadas apresentam teores reduzidos de Mg(OH)2 enquanto é produzida uma nova fase cristalina: hidromagnesita [Mg5 (CO3)4⋅(OH) 2⋅4H2O]. Após a carbonatação, o conteúdo de gel M-S-H é reduzido também, indicando uma carbonatação desta fase. A carbonatação aumenta a rigidez da matriz o que influi positivamente no desempenho mecânico e as propriedades físicas dos compósitos sem efeitos prejudiciais ao longo prazo. A adição de sepiolita em CCRF é estudada como possível adição na composição da matriz aglomerante. Baixos teores (1 e 2% em massa) de cimento são substituídos por sepiolita para o estudo das pastas de cimento hidratado e, posteriormente, dos compósitos. O Módulo Elástico Dinâmico das pastas é incrementado com o tempo pela adição de sepiolita. Os ensaios a flexão demostram que a adição de sepiolita melhora a homogeneidade dos compósitos. Reportam-se os efeitos das fibras de sisal após da exposição a sistemas MgO-SiO2 e PC e submetidas a diferentes condições de envelhecimento. Este estudo comparativo da degradação das fibras expostas a diferentes matrizes cimentícias mostra a compatibilidade das fibras lignocelulósicas com os cimentos à base de Mg. As fibras de sisal, inclusive após o envelhecimento acelerado, não apresentam nem redução significativa no conteúdo de celulose nem na cristalinidade da celulose assim como do tamanho de cristalito, quando expostas a cimentos MgO-SiO2.

A utilização de cinza volante na composição de material cimentício o torna mais sustentável, além de conferir à matriz hidratada características peculiares que melhoram o desempenho frente à ação de diferentes agentes deletérios. A principal desvantagem da utilização de pozolana no sistema cimentício é a maior susceptibilidade à carbonatação. A maior taxa de neutralização da solução aquosa dos poros é devida ao teor remanescente menor de portlandita na matriz. O conhecimento das características da cinza volante que influenciam a interação com a cal, é necessário para subsidiar medidas preventivas com relação ao consumo de portlandita. A presente pesquisa objetiva verificar a eficiência da adição de cal hidratada em concreto executado com cimento pozolânico como forma de reduzir a susceptibilidade à carbonatação. As etapas realizadas para cumprir o objetivo abrangem: a caracterização da cinza volante, com ênfase na determinação do teor de fase vítrea; a cinética de reação em sistema de cinza volante e hidróxido de cálcio; a evolução da hidratação, e a decorrente variação microestrutural. Nos sistemas cimentícios de concretos cujas composições são 100% de cimento ou 50% de cimento e 50% cinza volante, com e sem a adição de 20% de cal hidratada, foi caracterizado a microestrutura da camada de cobrimento e o seu desempenho frente à ação do anidrido carbônico, em ensaio acelerado. Na cinza volante estudada, o teor de fase vítrea foi de 57%, e o consumo máximo por atividade pozolânica, função da área específica BET, foi de 0,69 gramas de Ca(OH)2/grama de fase vítrea de cinza volante. No cimento portland pozolânico, este consumo é menor devido à estrutura formada pela hidratação do cimento. A adição de cal hidratada à pasta de cimento e cinza volante, além de aumentar o consumo de cal por atividade pozolânica, restabeleceu, parcialmente, o teor remanescente de portlandita na matriz. A interação da cinza volante com a cal hidratada não interfere no volume total de vazios da matriz hidratada, porém, refina a microestrutura, aumentando o volume de mesoporos. A carbonatação, em concretos com mesma resistência à compressão de 55 MPa, atingiu maior profundidade quando executado com cimento pozolânico. A adição de cal hidratada não foi eficiente em reduzir a susceptibilidade à carbonatação acelerada. / The use of fly ash in the composition of the cementitious material makes it more sustainable, besides conferring to the hydrated matrix peculiar characteristics which improve its performance with relation to the action of different deleterious agents. The main disadvantage of pozzolan utilization in cementious systems is its susceptibility to carbonation. The greatest neutralization rate of the aqueous solution of the cement pore is, generally, attributed to the smallest amount of portlandite remaining in the matrix. It is necessary to widen knowledge about the characteristics of the fly ash which influence the interaction with calcium hydroxide in order to promote preventive measures with regard to portlandite consumption. This current research aims at verifying the efficiency of hydrated lime addition to concrete by using pozzolanic cement as a way of reducing its susceptibility to carbonation. The steps employed to attain this objective include: fly ash characterization with an emphasis on glass content; fly ash and calcium hydroxide systems kinetics; hydration evolution; and the consequent microstructure variation. In cementious systems of concrete whose composition is either 100% cement or 50% cement and 50% fly ash _ with or without 20% addition of hydrated lime _ it was characterized the microstructure of covercrete and its performance with regard to the interaction with carbon dioxide in accelerated testing. In the studied fly ash, glass content was 57% and the maximum consumption per pozzolanic activity, which is function of BET specific surface area, was 0.69 g of Ca(OH)2/g of glass content in the fly ash. As far as pozzolanic Portland cement is concerned, this consumption is smaller due to the structure formed by the cement hydration. The addition of hydrated lime to the cement paste and fly ash, besides increasing the consumption of lime per pozzolanic activity, partially, reestablished the remaining content of portlandite in the matrix. The interaction of the fly ash with the hydrated lime does not interfere in the total volume of void spaces in the hydrated matrix; however, it refines the microstructure by increasing the volume of mesopores. Carbonation in concrete with the same compressive strength of 55 MPa reached its deepest point when performed in pozzolanic cement. The addition of hydrated lime was not efficient at reducing susceptibility to accelerated carbonation.