The construction industry is increasingly turning to the use of environmentally friendly materials in order to meet the sustainable aspect required by modern infrastructures. Consequently, for the last two decades, the expansion of this concept, and the increasing global warming have raised concerns on the extensive use of Portland cement due to the high amount of carbon dioxide gas associated with its production. The development of geopolymer concretes offers promising signs for a change in the way of producing concrete. However, to seriously consider geopolymer binders as an alternative to ordinary Portland cement, the durability of this new material should be evaluated in any comparative analysis. The main purpose of this study was to evaluate the durability characteristics of low calcium fly ash-based geopolymer concretes subjected to the marine environment, compared to ordinary Portland cement concrete with similar exposure. To achieve this goal, 8 molar geopolymer, 14 molar geopolymer and ordinary Portland cement concrete mixes were prepared and tested for exposure in seawater. Compressive strengths in the range of 2900 to 8700 psi (20-60 MPa) were obtained. The corrosion resistance performance of steel-reinforced concrete beams, made of these mixes, was also studied, using an accelerated electrochemical method, with submergence in salt water. The test results indicated that the geopolymer concrete showed excellent resistance to chloride attack, with longer time to corrosion cracking, compared to ordinary Portland cement concrete. / by Jean-Baptiste Edouard. / Thesis (M.S.C.S.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

The durability of Reinforced Concrete (RC) structures in the Marine environment is causing serious concern in the structural infrastructure. Reinforced concrete structures, exposed to aggressive environments, are expected to last with little or no maintenance for long periods of time. However, one of the most serious environmental exposures that causes degradation is Chloride Diffusion, due to shrinkage, atmospheric corrosion, and tide-induced wet and dry conditions at the air-water interfaces of coastal structures. Therefore, chloride diffusivity, which correlates with the electrical resistivity, has a significant impact on the durability of concrete. Concrete chloride diffusivity has been experimented by multiple agencies and researchers on sound concrete, but there is a considerable need for investigation of the durability of cracked concrete in the marine environment. The two test methods carried out are presented: Standardized American Society for Testing and Materials (ASTM) C1202 for Rapid Chloride Permeability (RCP) and ASTM D257 for Surface Resistivity (SR), and Nordtest (NT) Build 492 for Rapid Chloride Migration (RCM) and Bulk Resistivity (BR) for both sound (uncracked) and cracked (micro and macro) concrete. The limitations of the ASTM method, due to measurements before the steady-state migration is reached, does not account for leakage in cracked concrete, and the heating of the specimen due to higher current that increase the conductivity are indicated. The Rapid Chloride Migration test provides for the non-steady state of diffusion. Again, Bulk Resistivity, in contradistinction to Surface Resistivity is more accurate for cracked concrete. The correlation betweeen RCM-BR are plotted. Chloride Permeability/Migration is an important parameter that governs the Durability of Concrete. The principal contribution is the highlighting of the inadequacy of the current widely used standard ASTM C1202 for diffusivity testing, and the need for revision with further investigation. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

O fenômeno da carbonatação, como agente desencadeador do processo de corrosão de armaduras, assume especial importância quando as estruturas de concreto armado estão expostas a ambientes urbanos e à atmosfera poluída de gases como o CO2. O controle da profundidade de carbonatação do concreto exige o uso de ferramentas (modelos matemáticos) que representem o comportamento das variáveis que interagem no processo da carbonatação do concreto de forma clara e objetiva no sentido de auxiliar a compreensão do fenômeno. Nessa perspectiva, desenvolveram-se modelos computacionais que conjugam problemas complexos de modo simples. Entre esses modelos, citam-se as redes neurais artificiais, que têm inspiração no cérebro humano e que possuem a habilidade de aprender e generalizar possibilitando a resolução de problemas complexos. Neste trabalho é estudada a aplicação de redes neurais artificiais do tipo Perceptron multicamadas, com base no algoritmo de aprendizado supervisionado backpropagation, com o objetivo de obter um mapeamento entre as variáveis de entrada do problema relação água/cimento, distância do corpo de prova do mar e idade do corpo de prova e a variável de saída de interesse profundidade de carbonatação do concreto. Os resultados obtidos validam que os modelos de redes neurais artificiais se constituem numa importante ferramenta de avaliação da profundidade de carbonatação do concreto armado / The phenomenon of carbonation as the triggering agent in the process of reinforcement corrosion is particularly important when concrete structures are exposed to urban environments and the atmosphere contamination with gases such as CO2. The concrete carbonation depth control requires the use of tools (mathematical models) that represent the behavior of the variables that interact in the process of concrete carbonation in a clear and objective way to help understand the phenomenon. In this perspective, computer models have been developed to combine complex problems in a simple way. Among those models are the artificial neural networks, which have been inspired on human nervous system and have the ability to learn and generalize, making it possible to solve complex problems. This work studied the application of artificial neural networks like multilayer perceptron, based on backpropagation, supervised learning algorithm in order to obtain a mapping between the input variables of the problem ─ the water/cement (w/c) ratio, body of proof distance from the sea and age of the body of proof ─ and the output variable of interest ─ the depth of concrete carbonation. The results validate that the use of artificial neural networks is an important tool to evaluate concrete carbonation

A corrosão por cloretos é considerada por muitos pesquisadores a mais severa das manifestações patológicas que atacam as armaduras. O objetivo principal deste trabalho é avaliar a presença de cloretos livres em concreto de cimento Portland pelo método de aspersão de solução de nitrato de prata. A verificação de ataque por cloreto na estrutura é normalmente feita através de exames laboratoriais, demorados em que apresentam um custo muito alto. Pesquisando a aplicabilidade do método de aspersão de nitrato de prata in loco, em materiais à base de cimento Portland como indicador com capacidade de informar a presença ou não de contaminação por cloretos, evitando assim de imediato o teste laboratorial. Para que os resultados destes ensaios tivessem credibilidade quanto à presença de cloretos livres nas amostras, foi realizado, paralelamente à aspersão de nitrato de prata, um acompanhamento das amostras através de ensaios eletroquímicos. Observou-se com os resultados experimentais da pesquisa que a aplicabilidade do método de aspersão de solução de nitrato de prata vem a ser de grande relevância para o meio técnico, por ser um método qualitativo, de fácil aplicação, barato e provendo informações rápidas para que os profissionais da área de engenharia possam diagnosticar com segurança as estruturas com corrosão contaminadas por cloreto / The corrosion by chlorides is considered by a number of researchers the most dangerous pathological manifestation attacking concrete reinforcements. The assessment of the attacks to the structure by sodium chloride is usually done in the laboratory, takes too long and costs too much. The.main reason for this work is to assess the presence of free chlorides in Portland cement concrete and mortar through the silver nitrate aspersion method, which is justified by the fact that Our objective is to evaluate the applicability of the silver nitrate aspersion method in loco, in Portland-cement-based materials as indicators capable of showing the presence or not of contamination by chlorides, avoiding the immediate need for lab tests. So as to give credibility to the test for presence of free chlorides in the samples, these were checked by means of electrochemical tests in parallel with the silver nitrate aspersion. The experimental results of these tests showed that the applicability of the silver nitrate aspersion method seems to be of great relevance in the technical environment, as it is a qualitative method, easily applicable, inexpensive and capable of providing quick information so that professionals can safely diagnose the levels of chloride corrosion in the structures

De nos jours, le béton est le matériau de construction le plus utilisé dans le monde en raison de ses performances mécaniques, sa facilité de mise en oeuvre, son coût compétitif et sa « recyclabilité ». Toutefois, compte tenu de son caractère fragile en terme mécanique et de sa faible résistance à la traction, il est souvent renforcé par des armatures métalliques qui lui confèrent une bonne ténacité et une meilleure aptitude à supporter les efforts de traction. Ce composite béton-armature ne peut cependant assurer efficacement son rôle que si les deux composants sont étroitement liés l’un à l’autre. C’est donc dans la qualité de l’adhérence que réside l’efficacité du transfert des efforts entre les deux matériaux. Or, dès la mise en place des ouvrages en béton armé et pendant toute la durée de leur exploitation, différentes actions et agents agresseurs peuvent modifier la qualité de cette adhérence. Il peut s’agir de phénomènes naturels comme le gel/dégel et l’action du dioxyde de carbone atmosphérique, ou des sollicitations accidentelles comme l’incendie ou encore l’action de certains agents spécifiques comme les chlorures et les sulfates. Notre objectif dans cette thèse est de qualifier les modifications d’adhérence qui résultent de quatre types de sollicitations couramment rencontrées dans la vie des ouvrages en béton armé: l’effet des températures élevées, l’effet de la carbonatation, l’effet des cycles gel/dégel, l’effet de la corrosion. Nous évaluons la qualité de l’adhérence par la mesure de la résistance à l’arrachement et par l’analyse du comportement résiduel sous sollicitation mécanique. La technique d’émission acoustique est utilisée pour localiser en temps réel, l’endommagement du matériau sous sollicitation. Les applications de notre étude concernent non seulement les armatures et inserts classiques du béton armé mais aussi les nombreux dispositifs constructifs des structures mixtes acier – béton qui utilisent les liaisons par goujons pour relier les deux matériaux. / Nowadays, concrete is the most used construction material in the world because of its mechanical performances, its ability to be molded or cast, its competitive cost and its recyclability. However, concrete has a low ductility and a relatively low tensile strength compared to other construction materials. Therefore, concrete is often reinforced by steel rebars to improve the ductility and tensile strength. Nevertheless, to make reinforced concrete being highly efficient material, the two components need to be correctly bonded each to other. The bond quality the efficiency of the force transfer between rebar and concrete surrounding ensures. In fact, since the casting of concrete and during the service life of reinforced concrete structure, various actions such corrosion action, freeze/thaw attack and chemical attack etc. may affect the bond quality. The objective of this PhD research work is to qualify the changes of adhesion property causing by four types of action which frequently takes place in the service life of reinforced concrete structures: the effect of high temperatures, the effect of carbonation, the effect of cycles freeze/thaw, the effect of corrosion. The concrete-rebar bond quality is evaluated by doing pull-out tests under static mechanical action and measuring the bond strength and analyzing residual behaviour. Moreover, the acoustic emission technique is used to locate the cracks and evaluate the cracking evolution in real time. The founding of this study can be also extended to apply to other concrete-steel structures like composite structures in which headed studs are used to connect steel profiles to concrete.

Made available in DSpace on 2017-06-01T17:57:31Z (GMT). No. of bitstreams: 1 dissertacao_carlos_alberto.pdf: 1579628 bytes, checksum: ac1de165bd37e65d9cb3872ad819860e (MD5) Previous issue date: 2011-03-31 / The phenomenon of carbonation as the triggering agent in the process of reinforcement corrosion is particularly important when concrete structures are exposed to urban environments and the atmosphere contamination with gases such as CO2. The concrete carbonation depth control requires the use of tools (mathematical models) that represent the behavior of the variables that interact in the process of concrete carbonation in a clear and objective way to help understand the phenomenon. In this perspective, computer models have been developed to combine complex problems in a simple way. Among those models are the artificial neural networks, which have been inspired on human nervous system and have the ability to learn and generalize, making it possible to solve complex problems. This work studied the application of artificial neural networks like multilayer perceptron, based on backpropagation, supervised learning algorithm in order to obtain a mapping between the input variables of the problem ─ the water/cement (w/c) ratio, body of proof distance from the sea and age of the body of proof ─ and the output variable of interest ─ the depth of concrete carbonation. The results validate that the use of artificial neural networks is an important tool to evaluate concrete carbonation / O fenômeno da carbonatação, como agente desencadeador do processo de corrosão de armaduras, assume especial importância quando as estruturas de concreto armado estão expostas a ambientes urbanos e à atmosfera poluída de gases como o CO2. O controle da profundidade de carbonatação do concreto exige o uso de ferramentas (modelos matemáticos) que representem o comportamento das variáveis que interagem no processo da carbonatação do concreto de forma clara e objetiva no sentido de auxiliar a compreensão do fenômeno. Nessa perspectiva, desenvolveram-se modelos computacionais que conjugam problemas complexos de modo simples. Entre esses modelos, citam-se as redes neurais artificiais, que têm inspiração no cérebro humano e que possuem a habilidade de aprender e generalizar possibilitando a resolução de problemas complexos. Neste trabalho é estudada a aplicação de redes neurais artificiais do tipo Perceptron multicamadas, com base no algoritmo de aprendizado supervisionado backpropagation, com o objetivo de obter um mapeamento entre as variáveis de entrada do problema relação água/cimento, distância do corpo de prova do mar e idade do corpo de prova e a variável de saída de interesse profundidade de carbonatação do concreto. Os resultados obtidos validam que os modelos de redes neurais artificiais se constituem numa importante ferramenta de avaliação da profundidade de carbonatação do concreto armado

In recent years there has been a significant increase in the production of concretes for agricultural buildings, especially in the area of exposure to higly chemically aggressive environments. The aim of the thesis is to describe and summarize the existing knowledge about the durability of concrete exposed to the effects of highly chemically agressive environment. Furthermore, emphasis is placed on the description of individual additives and admixtures increasing the resistance of concrete to the effect of harmful substances. In the experimental part, the effects of individual types of additives, admixtures and sealing coatings on increasing the resistance of concrete against the effect of highly chemically aggresive environment are investigated in the laboratory.

No description available.

Comparative studies of nondestructive evaluation methods have shown that nonlinear ultrasonic techniques are more sensitive than conventional linear methods to changes in material microstructure and the associated small-scale damage. Many of the material degradation processes such as carbonation in concrete, corrosion in metals, etc., begin at the surface. In such cases, ultrasonic Rayleigh surface waves are especially appropriate for detection and characterization of damage since their energy is concentrated in the top layer of the test object. For the civil engineering infrastructure, only a limited number of field applicable nonlinear ultrasonic techniques have been introduced. In this paper a nonlinear ultrasonic measurement technique based on the use of Rayleigh waves is developed and used to characterize carbonation in concrete samples. Wedge transducer is used for the generation and an accelerometer for detection of the fundamental and modulated ultrasonic signal components. The measurements are made by varying the input voltage and along the propagation distance. The slope of the normalized modulated amplitudes is taken as the respective nonlinearity parameter. Concrete samples with two different levels of damage are examined, and the difference of the two fundamental frequencies is used to quantify damage state.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Diante da exposição à névoa salina, as estruturas em concreto podem sofrer ataques por cloretos, provocando corrosão das armaduras. As peças com faces voltadas aos ventos dominantes estão mais suscetíveis, especialmente aquelas que possuem grande superfície em relação ao volume, como são os casos de pilares e vigas. Este trabalho tem como objetivo avaliar os níveis de agressividade marinha, na orla marítima do Bairro de Boa Viagem, Recife-PE, em função de sua distância em relação ao mar, medindo a taxa de deposição de cloretos, pelo método da vela úmida, tendo como apoio o monitoramento do ambiente. Os resultados indicam que os íons cloreto chegam à superfície das estruturas a distintos níveis de concentração, dependendo da distância em relação à sua fonte geradora, no caso, o mar. Conclui-se que a deposição de cloretos decresce, numa relação do tipo exponencial, à medida que há um aumento do distanciamento em relação ao mar, e que a agressividade é significativa até 400 m da orla marítima / Exposing concrete structures to the saline mist, they can suffer chlorides attacks and could cause reinforcement corrosion. The structures parts with faces directed to dominant winds are more susceptible, especially those with great surface in relation to the volume, such as pillars and beams. This work objective is to evaluate the level of marine aggressiveness, in marine edge of Boa Viagem quarter, Recife-PE, in function of the distance to the sea, measuring the value of chloride deposition, using the wet candle method, with the support of the environment management. The results indicate that chloride ions reach surface structure in different levels of concentration, depending on the distance from its origin, in this case, the sea. The conclusion is that chloride deposition decreases, in an exponential relation, when there is an increase of the distance to the sea, and that aggressiveness is significantly as far as 400 m from the marine edge