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.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2016-10-03T11:31:01Z No. of bitstreams: 2 Dissertação - Plínio Ferreira Pires - 2016.pdf: 6131513 bytes, checksum: 8fa6643740293050fba973c250df0e54 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-10-03T11:31:21Z (GMT) No. of bitstreams: 2 Dissertação - Plínio Ferreira Pires - 2016.pdf: 6131513 bytes, checksum: 8fa6643740293050fba973c250df0e54 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2016-10-03T11:31:21Z (GMT). No. of bitstreams: 2 Dissertação - Plínio Ferreira Pires - 2016.pdf: 6131513 bytes, checksum: 8fa6643740293050fba973c250df0e54 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-07-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The carbonation phenomenon consists in a physicochemical process which reduces the alkalinity of concrete. Carbonation can destabilize the protective layer of the steel, leaving it susceptible to corrosion, which is one of the most significant and costly causes of deterioration in reinforced concrete. Accordingly, chemical analysis of the pore solution has been held for about 60 years, but few studies are focused on types of concrete containing mineral additions subjected to carbonation, due to the difficulty of obtaining the pore solution, given its structure densification under these conditions. Depending on the concrete composition, the natural carbonation process can take several years to present sufficient analyzable data, therefore, most of the studies on this topic use accelerated tests to simulate this phenomenon. However, even with full control of the laboratory environment, it is not possible to reproduce the randomness of the variables responsible for the degradation that occur in real situations. This study aims to evaluate the process of natural carbonation in 36 different types of concrete or analysis conditions, which cover a wide range of characteristics and properties of concrete that represent the various service situations of the structures, after about 14 years of exposure, in typical urban environment. The results are presented for types of concrete with and without mineral additions (silica fume, rice husk ash, metakaolin, fly ash and blast furnace slag); three water/binder (0.40, 0.55 and 0.70) and two curing conditions (dry-cured and moist-cured). The study was conducted by the application of simplified models of carbonation and statistical analysis on an extensive experimental database (over 2000 measurements) obtained by eight evaluations of carbonation carried at different ages, through 14 years of natural exposure prototypes of concrete beams. In addition, chemical analysis of pH, ionic strength and conductivity of the pore solution - obtained through innovative method - were conducted in both the carbonated layer and the non-carbonated layer of concrete. The results indicate that the empirically-analytical model proposed by Tuutti, has an excellent representativity of carbonated depth over time. The use of a coefficient of carbonation, from Tuutti’s model, calculated from early ages, can generate mistaken conclusions: underestimating the dry-cured concrete and overestimating the moist-cured concrete. In the overall analysis of the natural carbonation coefficients obtained by ANOVA showed that the water/binder ratio is the most significant factor, followed by curing type and, finally, the type of addition. The best performances as the carbonation are observed to the lower water/binder concretes, subjected to wet cure. Under the method used to obtain the pore solution, it was possible to compare the difference between the chemical properties of non-carbonated and carbonated layers of each type of concrete analyzed. / O fenômeno da carbonatação consiste em um processo físico-químico que leva à redução de alcalinidade do concreto. Isto pode desestabilizar a camada protetora do aço, deixando-o passível de corrosão, que é uma das mais importantes e onerosas causas de deterioração do concreto armado. Nesse sentido, a análise química da solução do poro tem sido realizada há cerca de 60 anos, contudo raros trabalhos focam em concretos submetidos à carbonatação contendo adições minerais, dada a dificuldade de se obter a solução devido à densificação na estrutura porosa nessas condições. Dependendo da composição do concreto, o processo de carbonatação natural pode levar vários anos para apresentar dados passíveis de análise, diante disso, a maioria dos estudos nesse tema utilizam ensaios acelerados para simular tal fenômeno, contudo, mesmo com todo controle do ambiente de laboratório, não se pode reproduzir a aleatoriedade das variáveis que ocorre em situações reais de degradação. Este trabalho tem como objetivo avaliar o processo de carbonatação natural em 36 diferentes concretos ou condições de análise, os quais cobrem uma ampla faixa de características e propriedades dos concretos, representando as mais diversas situações de serviço para as estruturas, após cerca de 14 anos de exposição, em ambiente típico urbano. São, portanto, apresentados resultados de concretos sem e com adições minerais (sílica ativa, cinza de casca de arroz, metacaulim, cinza volante e escória de alto-forno); três relações água/ligante (0,40; 0,55 e 0,70) e duas condições de cura (seca e úmida). O estudo se deu por meio de aplicações de modelos simplificados de carbonatação e análises estatísticas em um extenso banco de dados experimentais (mais de 2000 medidas) obtido por oito avaliações da frente de carbonatação realizadas em diferentes idades, durante 14 anos de exposição natural de protótipos de vigas de concreto. Foram realizadas também análises químicas de pH, força iônica e condutividade da solução do poro, obtida através de método inovador, tanto da camada carbonatada quanto da camada não carbonatada dos concretos. Os resultados indicam que o modelo empírico-analítico, proposto por Tuutti, possui excelente representatividade da profundidade carbonatada ao longo do tempo. A utilização de um coeficiente de carbonatação, do modelo de Tuutti, calculado a partir de idades iniciais pode gerar conclusões equivocadas: subestimando os concretos sem cura e superestimando os de cura úmida. A análise global dos coeficientes de carbonatação, obtidos pela ANOVA, demonstrou que a relação água/ligante é o fator mais significativo, seguido do tipo de cura e, por último, o tipo de adição. Os melhores desempenhos quanto à carbonatação são observados para os concretos de menor relação água/ligante, submetidos à cura úmida. De acordo com o método empregado para obtenção da solução do poro, foi possível comparar a diferença entre as propriedades químicas da camada não carbonatada e a carbonatada, para toda a família de concretos analisada.

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.

The corrosion study in actual concrete structures is a subject enough discussed as much in the academic ambience as in the professional one. The subject is relevant due the numberless pathology cases of corrosion in structural concrete that are reported, almost daily, in the technical sphere. Nevertheless, few are the studies on this phenomenon in structural concrete of the first half of the 20th century. Is common sense that these structures were executed in a different way from the actual, and its behavior in front of corrosion may be differentiated, however, little are the studies that analyze the behavior of these structures in front of this pathology. This dissertation, based on bibliographical study and author s experience, look for not only analyze the concrete structure characteristics of the first half of 20th century and its influence on the rebar corrosion, as also propose a methodology for its detection. The proposition of this theme is based in fact that many execution and calculus methods were enough different from the actual concerning the concrete structures. The sodium chloride and calcium chloride addition in concrete, with purpose to accelerate the set and curing of concrete, the use of wooden pins as spacers are some characteristics showed in this work. As conclusion, is proposed an evaluation methodology which permits analyze such structures under the optics of its peculiar characteristics, aiming at the rebar corrosion. / O estudo da corrosão em estruturas de concreto armado atuais é um assunto bastante discutido tanto no meio acadêmico, como no profissional. O tema reveste-se desta importância devido aos inúmeros casos de patologias de corrosão em estruturas de concreto armado que são reportados, quase diariamente, ao meio técnico. No entanto, pouco se tem estudado a respeito desse fenômeno em estruturas de concreto armado da primeira metade do século XX. É senso comum que essas estruturas foram executadas de forma diferente das atuais e que seu comportamento frente à corrosão pode ser diferenciado; no entanto, são poucos os estudos que analisam o comportamento desse tipo de estrutura frente a essa patologia. Este trabalho, tendo por base um estudo bibliográfico e a experiência do autor, busca não só analisar as características das estruturas de concreto armado da primeira metade do século XX e suas influências sobre a corrosão das armaduras, como também propor uma metodologia para sua detecção. A proposição desse tema baseia-se no fato de que muitos métodos de execução e cálculo eram bastante diferentes dos atuais no que concerne a estruturas de concreto armado. A adição de cloreto de sódio e cloreto de cálcio no concreto, com a finalidade de acelerar a pega e a cura do concreto, e o uso de tarugos de madeira como espaçadores são algumas das características mostradas neste trabalho. Como conclusão é proposta uma metodologia de avaliação que permita analisar tais estruturas sob a ótica de suas características particulares, com vistas à corrosão da armadura.

La corrosion des armatures est reconnue comme la première cause de dégradation des structures en béton armé dans les domaines du génie civil et des monuments historiques. La corrosion peut survenir lorsque le béton d'enrobage est carbonaté ou lorsque les ions chlorure sont présents en quantité suffisante au niveau de l'armature.Les objectifs de cette thèse visent à appréhender les processus de corrosion des armatures lorsque le béton est doublement contaminé (carbonatation et ions chlorure) et d'évaluer une solution de réparation de type traitement électrochimique d’extraction des ions chlorure (ECE).Pour répondre à ces objectifs, trois phases ont été programmées : (1) des vieillissements artificiels, (2) un traitement ECE et (3) un suivi de la durabilité du traitement. Pour chacune de ces phases, les évolutions (1) de la corrosion des armatures dans le béton, (2) des produits de corrosion à l'interface armature/béton et (3) de la matrice cimentaire ont été investiguées. L'approche scientifique de l'étude, avec des analyses multiples d'observations à différentes échelles et l'utilisation de techniques non destructives, destructives ou in situ, a permis de rendre compte des processus de corrosion avant et après traitement et de discuter les résultats en fonction de critères d'efficacité proposés.L'étude a été réalisée en prenant en compte deux ciments (CEM I et CEM III/A) et en considérant deux modes de vieillissements artificiels. Trois cent vingt éprouvettes en micro-béton armé répondant à quatre formulations ont ainsi été étudiées. Les techniques principales utilisées sont des caractérisations électrochimiques non destructives, des caractérisations au MEB et EDS, des analyses destructives de déterminations quantitative pour la teneur en ions chlorure et qualitative pour l'évaluation du pH et enfin la microspectrométrie Raman qui permet de déterminer la nature des produits de corrosion in situ.L’exploitation de l’ensemble des résultats a mis en évidence l’évolution des caractéristiques étudiées au cours des phases de l’étude. Avant traitement, l'enrobage béton était entièrement carbonaté et la teneur en ions chlorure libres au voisinage de l'armature était comprise entre 0,9 et 2,1% par rapport à la masse de ciment en fonction des formulations. Les courants de corrosion étaient de l’ordre de 10 µA/cm² et une épaisseur de corrosion homogène de l’ordre de 5-10 µm était observée. Lors des analyses Raman in situ, de la rouille verte chlorurée a été identifiée, synonyme de corrosion active. Après traitement, plus de 90% des ions chlorure ont été extraits et le pH du béton au voisinage de l'armature a augmenté (pH>9) sur une épaisseur d’environ 1 cm. Les courants de corrosion sont devenus inférieurs à 0,1 µA/cm² (niveau de corrosion négligeable). La formation de magnétite a majoritairement été observée avec néanmoins la présence résiduelle très locale de rouille verte. Aucune évolution délétère significative de la matrice cimentaire n’a été identifiée. L’efficacité du traitement a donc été démontrée. L'évaluation de la durabilité du traitement sur une période de 4 à 12 mois a montré que les caractéristiques électrochimiques restaient stables. En revanche, la diminution de l'épaisseur de béton dont le pH avait augmenté pour les éprouvettes fabriquées avec le ciment CEM III/A peut laisser craindre une reprise de corrosion sur du plus long terme. Enfin, le suivi Raman in situ, montre des différences de la durabilité en fonction de la durée du traitement / Reinforcement corrosion is known as the first cause of reinforced concrete degradation in the fields of civil engineering structures and historical monuments. Corrosion occurs when concrete cover is carbonated or when chloride ions are present in sufficient quantity at the reinforcement vicinity.The main objectives of this thesis are to investigate the corrosion processes of the reinforcement when the concrete is contaminated by carbonation as well as chloride ions and to evaluate a cathodic electrochemical treatment as a repair solution.To meet these objectives, three phases were investigated: (1) artificial agings, (2) an electrochemical chloride extraction (ECE) treatment and (3) durability. For each of these phases, the evolutions (1) of the rebar corrosion in concrete, (2) of the corrosion products at the reinforcement/concrete interface and (3) of the cementitious matrix were studied.The scientific approach gathered multiple analyzes at different scales and the use of non-destructive, destructive or in situ technique. It allowed to study the corrosion processes before and after treatment and to discuss results according to efficiency criteria suggested.The study was carried out taking into account two cements (CEM I and CEM III/A) and considering two modes of artificial aging. More than three hundred specimens of reinforced micro-concrete, corresponding to four concrete designs, were therefore studied. The main techniques used were non-destructive electrochemical characterizations, SEM and EDS characterizations, destructive quantitative determinations (chloride ion content) and qualitative determinations (pH evaluation), and finally Raman microspectrometry to determine the nature of the corrosion products.The results highlighted some evolutions of different characteristics studied during the phases of the study. Before treatment, the concrete cover was entirely carbonated and the free chloride content at the reinforcement level was in the range of 0.9-2.1% by weight of cement depending on the concrete design. A 10 μA/cm² average corrosion currents was reported and a homogeneous corrosion layer thickness of about 5-10 μm was observed. During in situ Raman analysis, chloride green rust was identified indicating an active corrosion.After treatment, more than 90% of the chloride ions were extracted and the thickness of the concrete which had a pH value higher than 9 around the reinforcement, was about 1 cm. The corrosion currents became less than 0.1 μA/cm² (negligible corrosion level). The formation of magnetite was mostly observed with nevertheless a local presence of residual green rust. No significant deleterious evolution of the cementitious matrix was identified. The treatment efficiency was therefore demonstrated. The evaluation of the treatment durability over a period of 4 to 12 months showed that the electrochemical characteristics remained stable. On the other hand, a decrease in the concrete area which pH increased during the electrochemical treatment was observed for CEM III/A cement which could lead to a corrosion recovery over the longer term. Finally, the in situ Raman study revealed differences in durability as a function of the treatment duration

L’encrassement des façades d’immeuble est causé par un phénomène d’altération biologique essentiellement esthétique. Leur vieillissement naturel favorise la colonisation de micro-organismes. La cinétique de biodétérioration dépend de plusieurs paramètres, tels que la situation géographique, les conditions environnementales et les caractéristiques physico-chimiques du matériau. L’objectif de la présente étude est d’établir un lien entre la composition chimique de mortiers à base de ciments et leur cinétique de colonisation par des microorganismes. Deux bancs d’essais sont utilisés : un banc d’essai in situ et un banc d’essai de biodétérioration accélérée de laboratoire. Deux ciments Portland (OPC) et deux ciments alumineux (CAC) de minéralogies différentes ont été sélectionnés. L’effet de la porosité, de la rugosité et de la carbonatation a également été étudié. Le microorganisme sélectionné pour les essais de laboratoire est l’algue Klebsormidium flaccidum qui se développe de manière prépondérante sur les façades en France. Les résultats obtenus en laboratoire et in situ montrent que la biocolonisation des mortiers à base de CAC est plus lente que celle des mortiers à base d’OPC. Lorsque la porosité augmente, la vitesse de biocolonisation augmente et l’effet de la composition chimique est en grande partie masqué. La biocolonisation des mortiers carbonatés se réalise plus rapidement que celle des mortiers non carbonatés surtout dans le cas des mortiers à base d’OPC. Enfin, les mortiers de surface rugueuse sont colonisés plus rapidement quelle que soit la formulation testée. Cet effet est plus marqué pour les mortiers exposés in situ que pour ceux testés en laboratoire. / The fouling of building-facade is caused by a main aesthetic phenomenon of biological weathering. The natural weathering favors the micro-organisms development. The biofouling kinetics depends on several parameters such as geographical situation, environmental conditions and physicochemical parameters of substrates. The main objective of this study is to highlight the influence of the mortar chemistry in relationship with its physical properties on the algal growth. The biofouling kinetics was followed on samples exposed outdoor and on samples tested in a laboratory bench which consists in spraying an algal culture on mortar specimens. In order to characterize the influence of the mortar chemistry on biofouling, two Portland cements (OPC) and two calcium aluminate cements (CAC) were tested. The influence of roughness, porosity and carbonation was also studied. The green algae Klebsormidium flaccidum were chosen for the accelerated laboratory tests because of its representativeness. The results obtain in laboratory and in situ show that CAC based mortars slow down the colonization kinetics compared to OPC based mortars. When porosity increases the biofouling kinetics increases and the effect of the mortars chemical composition is largely hidden. The carbonated mortars biofouling is achieved more quickly than uncarbonated ones especially for OPC based mortars. Finally, the rough surfaces are colonized faster whatever formulation tested. This parameter is mostly highlighted for in situ tests.

O uso de fibras vegetais e de cimentos alternativos – ambos provenientes de resíduos, é tido como boa opção na busca por novos fibrocimentos. Entretanto, a maioria das pesquisas desenvolvida nos últimos anos tem apresentado resultados desanimadores no que se refere à durabilidade do material. Além disso, os métodos para avaliação do desempenho ao longo do tempo de materiais reforçados com fibras sensíveis a álcalis ainda não estão bem estabelecidos. O trabalho avaliou o comportamento de compósitos produzidos com cimento de escória de alto-forno reforçados com fibras de celulose, moldados através de adaptações dos processos industriais usados em todo mundo pelas empresas de fibrocimento. Em seguida, a durabilidade das formulações foi avaliada através de ensaios de envelhecimento, os quais se basearam na simulação dos principais agentes e mecanismos de degradação atuantes no material. O desempenho físico e mecânico dos compósitos foi avaliado através da análise de propriedades pré-estabelecidas, consideradas importantes no emprego material como componente construtivo. A análise dos resultados confirmou a eficiência da incorporação da celulose nas propriedades mecânicas do compósito. A durabilidade do material foi diferente para as matrizes empregadas. As matrizes ativadas com gipsita e cal hidratada (EGCH) foram menos agressivas às fibras, entretanto apresentaram problemas de hidratação às primeiras idades e perda de resistência devido à carbonatação. A matriz ECP, mais alcalina, apresentou resultados superiores de resistência mecânica nas primeiras idades. Ela decompôs as fibras e reduziu as propriedades mecânicas durante o envelhecimento. A carbonatação reduziu o ataque alcalino às fibras nestas matrizes, estabilizando a resistência mecânica e a perda de tenacidade não foi tão acentuada. A metodologia de envelhecimento acelerado que combinou ciclos de molhagem e secagem à carbonatação se mostrou eficiente na simulação do envelhecimento natural. / Vegetable fibers and alternative cements from residues is a good option for replacement asbestos-cement. However, research development has presented no satisfactory results concerning material durability and methods of performance evaluation to reinforced materials with alcali sensitive fibers are not well developed. The objetives of this research are: a) evaluation of composites behavior produced with blast-furnace slag reinforced with residual cellulose fibers, which were moulded in adapted conventional industrial processes, common in fibercement companies around world and b) durability performance evaluation applying proposed aging tests. Aging tests were based on simulation of main agents and degradation mechanisms. Physical and mechanical behaviour of composites was evaluated considering important properties in building component uses. Cellulose fibers improved the mechanical properties of the composites. Durability presented different results for the two matrices. The matrices activated with gypsum and hidrated lime (EGCH) have been less aggressive than matrix activated with ordinary Portland cement (OPC) in relation to fibers. However, they presented problems concerning to the hydration at early dates and loss of resistance due to carbonation. Matrices activated with OPC presented better results of MOR at the early dates. In fact, they are more alkaline and they decomposed fibers and reduced the mechanical properties during the aging. The carbonation reduced the alkaline attack, stabilizing the MOR and reducing the loss of tenacity. The accelerated methods with carbonation were efficient in the simulation of the natural ageing.

Philosophiae Doctor - PhD / Coal combustion accounts for 95% of electricity generation in South Africa while globally coal combustion for energy generation stands at 42%. It has been predicted that coal utilization for energy generation will continue due to its low cost and availability in huge quantities in different parts of the world. Additionally brine and gaseous emissions are produced in the power generation and coal combustion processes. In fact, it has been established that CO2 emissions from power plants are the main cause of the green-house effect leading to global warming. Mitigation of the effects of disposal of fly ash, brine and CO2 emissions is critical for sustainable energy generation from coal and environmental protection. The study investigated whether South African coal fly ash could be used for brine remediation and CO2 capture using fly ash based hydrotalcites and zeolites. Four main objectives were investigated. These were; firstly, to compare the natural CO2 capture potential of a power station ash dam with an accelerated ex-situ mineral carbonation process. Secondly, to probe the effect of accelerated ex-situ mineral carbonation on brine quality with regards to major, minor and trace elements concentration. Furthermore, the study investigated the feasibility of synthesizing hydrotalcites from fly ash by optimizing the synthesis parameters such as acid concentration, aging time, aging temperature, pH during aging, crystallization time and crystallization temperature. Finally the study compared the CO2 adsorption capacities of the fly ash based hydrotalcites with fly ash based zeolites NaA, and NaX. The natural carbonation potential of the wet disposed ash dam at Secunda was investigated by coring a 20 year old dam. Three cores (SI, S2 and S3) were obtained by air flush coring the dam along a geophysical line and establishing the geophysical profile of the three cores. The surface of the three cores was of medium resistivity with values between 9.3 and 12.2 nm while the midsections were of low resistivity with values ranging between 4 and 7 nm. The base section of core SI had a resistivity of 28.3 nm, that of S2 was between 16.2 and 21.4 nm and that of S3 between 12.2 and 16.2 nm; implying that SI had the lowest salt load while S3 had the highest salt content. Moisture content was observed to be high deeper down the profiles of S2 and S3 with samples appearing water logged while SI had the highest moisture content at the surface showing the inhomogeneity of the ash dam. The morphology of fresh fly ash taken from the ash collection hoppers at Secunda was observed to be spherical. Weathered ash from the ash dam showed irregularly agglomerated particles while accelerated ex-situ mineral carbonation resulted in the formation of acicular particles of calcite. Fresh ash, weathered ash and the accelerated carbonated ash were all class F with a sum total of silica, alumina and iron oxide totaling more than 70%. A reduction in silica and alumina content with instability of fly ash. Dumping of spent iron catalyst (resulting from the petrochemical operations as Sasol) on the ash dam led to an increase in Fe203 content of the weathered ash. Enrichment of Nb, Sr, Y, Th, Na, Cl, S04, K and S with natural carbonation as well as during accelerated ex-situ mineral carbonation was observed and was due to the contact of ash with brine during these two processes. Reduction of Zr, Rb, Pb, Ni, Co and V content of ash was observed with weathering. Mineralogically, all the ash samples had main phases of mullite, quartz, magnetite and hematite, with weathered and accelerated carbonated ash having additional phases of calcite. The aluminosilicious nature of the three ashes was identified by structural evaluation using Fourier transform infrared analysis which revealed that, bands associated with C-O in-plane and out of plane bending of carbonates was only visible in weathered and carbonated ash.

The corrosion of steel reinforcement is probably the most frequent type of degradation of reinforced concrete structures. Reinforcing bars are protected from corrosion by a thin iron oxide layer which is formed on their surface due to a high alkalinity of the surrounding concrete. Corrosion may start when this layer is destroyed (i) either by chloride ion penetration (when the concentration of dissolved chloride at the depth of the reinforcing steel exceeds a critical value) or (ii) by a reduction in the pH value of pore solution to values below 9.5. Such a reduction in alkalinity is the result of carbonation of the Ca(OH)2 in the concrete mass, i.e. of its reaction with the atmospheric CO2. The main aim of this work is an experimental investigation and modelling of carbonation process. The effect of relative humidity, curing period and replacement of Portland cement by supplementary cementing materials (SCM - fly ash, blast furnace slag and metakaolin) on carbonation process has been studied. Calcium hydroxide content in the presence of SCM and their pozzolanic activities have been also determined. Furthermore, lots of parametric studies and comparison of carbonation models have been provided. The software tools based on the introduced models and considering the input data to be statistically independent random variables have been described and used for other parametric studies.

This dissertation presents the study of freeze-thaw resistance of carbonated, low-lime calcium silicate cement based paste, mortar, and concrete and the pore system of these materials characterized by MIP, SEM, and image J analysis.