Tesi sul tema "Corrosion efficiency"

La détérioration d'une structure en béton peut être dû à de nombreux processus, qui agissent individuellement ou en synergie. Quelques exemples de processus qui causent la détérioration des matériaux cimentaires comprennent des attaques sulfatique, des cycles gel-dégel, de la carbonation ou des attaques salins provoquant la corrosion des armatures dans le béton. La corrosion des armatures est l'un des phénomènes les plus importants qui réduit la durée de vie des ouvrages en béton, en impactant de façon importante le budget maintenance de la structure affectée. L’objectif de ce travail est d'étudier la durabilité à long terme de différents inhibiteurs de corrosion. D’une part, trois inhibiteurs de corrosion sont choisis comme représentatifs : le nitrite de calcium (CNI), l’éthanolamine (AMA) et le sodium monofluorophosphate (MFP). Ils sont incorporés dans trois bétons différents : le béton de ciment Portland (OPCC), le béton de ciment reconstitué avec 70% de ciment Portland et 30% de laitier (BCC) et le béton prêt à l’emploi (RMC). Afin d'étudier l'efficacité de ces trois inhibiteurs, quatre approches sont employées : une à l’échelle de la solution interstitielle de béton, une à l'échelle de la solution extraite de ciment, une à l'échelle du mortier et une à l'échelle du béton. L'étude est réalisée en employant des méthodes électrochimiques et analytiques afin de caractériser le mécanisme d'inhibition en présence d'ions chlore. D’autre part, l'objectif de cette étude est d'explorer l'efficacité d'un nouveau pigment inhibiteur de zinc-phosphate (ZP) obtenu par la conversion chimique et le traitement électrochimique cathodique. Cette étude est réalisée à l’échelle de la solution interstitielle de béton ainsi qu’à à l'échelle du mortier
The deterioration of a concrete structure may occur due to many processes, which act individually or synergistically. Some examples of processes that cause material deterioration include alkali aggregate reactivity, sulphate attacks, freezing, thawing, cycling, carbonation or salt attack inducing corrosion of concrete reinforcement. Corrosion of reinforcing rebars is one of the most important phenomenon’s that reduce the service life of a concrete structure, and causes a huge impact on the maintenance budget of affected structure. The objective of this research work is to study the long-term durability of different corrosion inhibitors. On the one hand, three additive corrosion inhibitors are selected as representatives : one is a calcium nitrite based corrosion inhibitor (CNI), the other corrosion inhibitors are ethanolamine (AMA) and sodium monoflurophosphate (MFP). They were admixed in water before casting of three different concretes (Ordinary Portland cement concrete (OPCC), blended cement concrete prepared with 30% slag in mass substitution of Portland cement (BCC) and ready-mix concrete (RMC)). In order to characterize the effectiveness of these inhibitors, four approaches are used: one at the level of pore concrete simulating solutions, one at the solution extract of cement level, one at the mortar level and one at the concrete level. The study was performed through the using electrochemical and analytical methods to discuss the inhibition mechanism in the presence of chloride ions. On the other hand, the objective of this study is to explore the efficiency of a new inhibitive pigment zinc-phosphate (ZP) used as coating for rebars and obtained by chemical conversion and cathodic electrochemical treatment, to protect carbon steel rebar against the corrosion by chloride ions in fresh pore concrete simulating solutions and mortars

Ultramonit is a system under development for permanent installation on critical parts of the subsea oil- and gas pipelines in order to monitor the corrosion continuously by using ultrasound. The communication link which connects the Ultramonit units with the outside world is identified as the system’s bottleneck, and it is thus of interest to compress the ultrasonic data before transmission. The main goal of this diploma work has been to implement and optimize a lossy compression scheme in C on the available hardware (HW) with respect to a self-defined fidelity measure. Limited resources, such as memory constraints and constraints with respect to the processing time, have been a major issue during implementation. The real-time aspect of the problem results in an intricate relation between transfer time, processing time and compression ratio for a given fidelity. The encoder is optimized with respect to two different bit allocation schemes, two different filters as well as various parameters. Compared to transferring the unprocessed traces, the results demonstrate that the transfer time can be reduced with a factor 12. This yields acceptable fidelity concerning the main application of long term monitoring of subsea pipelines. However, for ultra-high precision applications where the total change in thickness due to corrosion is less than a few micrometers, compression should not be employed.

In this work, a comparative electrochemical study has been performed to evaluate corrosion inhibition property of several film-forming corrosion inhibitors provide by Akzo Nobel on carbon steel in a chloride solution. For carbon steel exposed to 1 M NaCl solution with and without added inhibitor, electrochemical measurements including electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) at different exposure time intervals, and potentiodynamic polarization at the termination of the exposure, have been performed to investigate the film forming process and to evaluate corrosion inhibition efficiency of the inhibitors, as well as its evolution with time. The corrosion resistance data obtained from the EIS and LPR measurements are in good agreement. The results indicate different inhibition properties of the inhibitors tested. The inhibition effect of SSF CI-1 is negligible in the first hour of exposure, but it increases steadily with time for 1 day, and then remains the same level during the exposure up to one week. SSF CI-2 exhibits a good inhibition effect in the first hour, but the effect decreases with time to a low level after 8 hours, and then increases again with prolonged exposure. SSF CI-4 shows a low inhibition effect during the first day, and then increases to a maximum level after three days’ exposure. For SSF CI-5 and SSF CI-6, the inhibition effect within 8 hours is relative low but higher than that of SSF CI-4, and the effect increases with time during prolonged exposure. The SSF CI-5 seems to be better than SSF CI-6 because of a more stable inhibition effect. The EIS results indicate that most of the inhibitors form a resistive surface film on carbon steel, which becomes more resistive and protective after several days’ of exposure. However, in the initial stage of exposure, the SSF CI-6 does not show an effect of formation of a resistive film on the surface. The potentiodynamic polarization measurements suggest that, SSF CI-1 and SSF CI-2 are anodic type inhibitor, SSF CI-4 is cathodic type inhibitor, and SSF CI-5 and SSF CI-6 are mix type inhibitor. Moreover, the inhibitors tested show a similar corrosion inhibition effect as mussel adhesive protein (MAP) at the low dosage level.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
A redução na emissão de CO2 na atmosfera é um dos desafios atuais mais importantes enfrentados por diferentes indústrias no mundo. A geração de energia através da queima de combustíveis fósseis utilizando oxigênio puro [1], também chamada de tecnologia de oxicombustão, é uma opção utilizada pelas indústrias de geração de energia para minimizar os índices de concentração de CO2 até emissão ZERO [1,2]. Inevitavelmente, as tubulações dos trocadores de calor que conformam aquelas plantas de energia, sofrem corrosão em contato com os gases de combustão (H2O-CO2) em altas temperaturas. Estas tubulações, fabricadas com aço ou com ligas ferro-cromo vem sendo utilizadas no intuito de reduzir a corrosão. Tubulações com revestimentos/recobrimentos protetores tem sido também considerados para aumentar a resistência a processos corrosivos sem requerer o emprego de ligas de alto custo. Um revestimento adequado deve ser inerte e estável em altas temperaturas como é o caso dos materiais cerâmicos. A alumina, sendo um material estável em ambientes característicos do processo de oxicombustão apresenta características favoráveis para esta proteção [3]. Amostras de Fe-Cr foram oxidadas sob condições que simularam processos de Oxicombustão nos laboratórios do Bundesanstalt Für Materialforschung Und-Prüfung (BAM) Berlim-Alemanha. O processo ocorreu a 650 graus Celsius durante 2000 h, em atmosfera contendo 60 por cento CO2,30 por cento H2O, 7 por cento N2, 2 por cento O2 e 1 por cento SO2. A caracterização microestrutural das amostras oxidadas foi realizada nos laboratórios do instituto Nacional de Tecnologia (INT), utilizando técnicas de Microscopia Eletrônica de Varredura (MEV) e Espectroscopia por Dispersão de Energia de Raios-X (EDS). Foram produzidos riscos na superfície do revestimento de Al2O3, previamente aos testes de oxidação, para simular falhas no revestimento; além da eficácia do revestimento de alumina, foi também avaliado o papel do cromo como meio protetor contra a corrosão e de outros elementos de liga no processo de oxidação do aço P92, buscando identificar o mecanismo de oxidação. Como resultado do fluxo dos gases de oxicombustão há formação de camadas de Fe3O4, Fe2O3 e cromo-espinélio nas ligas sem revestimento. As amostras que possuíam o revestimento de alumina apresentaram ótima proteção, com resultados de uma alta eficácia, enquanto as amostras que tinham riscos apresentaram uma oxidação interna de oxidação cromo-espinélio protetor na matriz logo abaixo da região afetada.
The reduction in the emission of CO2 in the atmosphere is one of the most important problems faced by different industries in the world. The generation of energy from oxyfuel oxygen, [1], also called Oxyfuel technology, is a matter of CO2 emission for ZERO [1,2]. Inevitably, as pipes of the heat exchangers that make up these power plants, they suffer corrosion in contact with the flue gases (H2O-CO2) at high temperatures. These pipes, made of steel or iron-chromium alloys, are not used instead of reducing corrosion. Pipes with protective coatings have already been submitted to increase resistance to corrosive processes without requiring the use of high cost alloys. One which must be inert and static at high temperatures is the case of ceramic materials. An alumina, being a suitable material to the environments characteristic of the Oxyfuel process, presents characteristics favorable to the protection [3]. Fe-9Cr samples were oxidized under conditions that simulated Oxyfuel processes in the laboratories of the Bundesanstalt Für Materialforschung Und-Prüfung (BAM) Berlin-Germany. The process occurred at 650 degree Celsius for 2000 h, in an atmosphere containing 60 percent CO2, 30 percent H2O, 7 percent N2, 2 percent O2 and 1 percent SO2. The microstructural characterization of the oxidized samples was performed in the laboratories of the National Institute of Technology (INT), using Scanning Electron Microscopy (SEM) and X-ray Energy Dispersion Spectroscopy (EDS) techniques. Risks were produced on the Al2O3 coating surface, prior to the oxidation tests, to simulate coating failures; besides the effectiveness of the alumina coating, the role of chromium as a protective medium against corrosion and other alloying elements in the oxidation process of P92 steel was also evaluated, in order to identify the oxidation mechanism. As a result of the flow of oxyfuel gases, Fe3O4, Fe2O3 and chromium-spinel layers are formed in the alloys without coating. The samples that had the alumina coating presented optimum protection, with results of a high efficiency, while the samples that had scratches presented an internal oxidation of protective chromium-spinel oxidation in the matrix just below the affected region.

Corrosion within the oil and gas sector is an ongoing concern for operators. The challenging nature of extraction and processing fluids is an unavoidable cause of severe metallic corrosion. With modern emphasis on health, safety and the environment, the case for managing corrosion has become an imperative agenda. Whilst new and more effective methods of mitigation are key, an interim solution is improving the value of current methods. A literature survey carried out within this project has revealed CO2 corrosion as contributing to most corrosion related failures within the industry. The corrosion behaviour in CO2 containing environments is complex partly due to the wide range of prevailing conditions such as temperature, CO2 concentration and flow conditions. For oil and gas transportation pipelines, internal corrosion mitigation can be achieved by the use of chemical inhibitors. Inhibitors have been established to be effective but are by no means a complete solution. Issues such as their effectiveness in high velocity and high shear flow are a main consideration for their function. The hydrodynamic nature of the flowing fluids can affect inhibitor efficiency by either slowing the rate of formation of the inhibitive layer or causing degradation of well-formed inhibitive layers. A combined effect may also be active. The corrosion behaviour of carbon steel in simulated oilfield conditions is investigated in this project with emphasis on conditions of varying velocity, impinging flow and consequently shear stress. Since inhibition is the main mitigation technique for fluid related corrosion, the efficiency of a commercially used inhibitor is, in this case assessed in the abovementioned conditions. To simulate both impingement and flow, a jet impingement apparatus is used in conjunction with a segmented-electrode specimen set up to separately study the erosion-corrosion behaviour of different hydrodynamic zones under the jet. Corrosion rates are measured by gravimetric analysis and results are also evaluated with electrochemistry. Additionally, galvanic interactions between the different hydrodynamic zones have been investigated. Visual and light-optical microscopic examinations are also used to assess variable effects within the zones. Under such conditions, the corrosion rates have been found to be significantly higher in impingement zones. Aerated conditions have shown a significant variation in corrosion behaviour between impingement and non-impingement zones. The results in CO2 saturated brines are consistent but with evidence of different relations between hydrodynamics and the corrosion rate. The inhibitor has been shown to be effective in CO2 saturated brines and significantly influenced by both inhibitor concentration and hydrodynamic conditions. Inhibitor efficiency has also shown a complex dependence on concentration and establishes a need to evaluate optimum inhibitor concentrations before field application. Evaluation of the mass loss results against electrochemistry has shown a large discrepancy between the two methods. This rather surprising result suggests solid-free flow is not entirely free of erosion and synergistic effects. This comprehensive study has not only improved current knowledge on the relation between hydrodynamics and inhibitor efficiency but also indicates a critical need to evaluate suitability of current monitoring methods. Electrochemical methods are increasingly used as a method of choice and while they contribute significant monitoring data, they are observed to be unable, alone, to monitor erosion and synergy. An industry review on their suitability to monitor solid-free flow corrosion is recommended.

Metallic additives, also known as anticorrosive pigments, can provide sacrificial cathodic protection and complement the barrier protection afforded by heterogeneous organic coatings to metallic substrates. The unique systematic study of the corrosion resistance of an epoxy coating reinforced with different sizes (80nm, 500nm, 10um) and continuous multiple pigment volume concentration (0, 2%, 10%, 20%, 45%) below global critical pigment volume concentration of zinc particles were studied. The thesis is developing the fundamental understanding to optimize corrosion protection and predicting the protection with time. The properties of these cathodic coatings were investigated by a single-frequency electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements that can be used as to understand cathodic protective state. Finite Element Analysis (FEA) has been applied here for modeling and simulating part of actual experiments. This thesis will help understanding the sensitivity and efficiency to various size and loading of metallic additives for corrosion protection.

Made available in DSpace on 2014-10-09T12:44:57Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:02:49Z (GMT). No. of bitstreams: 1 07005.pdf: 6131632 bytes, checksum: b80963599556c1f13207cf28f7929c5b (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Corrosion of steel reinforcement in concrete structures poses a risk reduction of durability and ability to perform the required function of structures for which they were designed.The objective of this work was to study the effectiveness of a new type of corrosion inhibitor with different concentrations of the active substance and its comparison with commercial products. The corrosion inhibitors were part of a comprehensive system repair materials from Betosan s.r.o. and using the electrical measurements was studied their effect in reducing corrosion activity caused by aggressive chloride environments.

Ces travaux présentent l'étude de transformateurs par voie acoustique, basés sur la technologie CMUT (Capacitive Micromachined Ultrasonic Transducer ), visant à développer des composants monolithiques assurant l'isolation électrique au sein de la commande des interrupteurs à semi-conducteurs. S'agissant de microsystèmes électromécaniques, les CMUTs offrent des perspectives intéressantes en terme d'intégrabilité monolithique avec les interrupteurs à semi-conducteurs. L'architecture proposée est constituée de deux transducteurs CMUTs de part et d'autre d'un substrat en silicium. Un outil de modélisation a été développé dans le but de prédire le comportement du transformateur. Des protocoles de mesure du rendement des dispositifs fabriqués ont été mis en place permettant une évaluation quantitative des performances des prototypes (un rendement de 32 % est atteint avec une marge de progression à 60 %). L'exploitation du modèle développé, et validé par les résultats de caractérisation, a permis de mettre en évidence les limites et perspectives d'amélioration de ces dispositifs
This work is a study of CMUT (Capacitive Micromachined Ultrasonic Transduer)based acoustical transformers as a step in the development of insulating components in semiconductor switches control chain. CMUT transducers being electromechanical systems (MEMS), their monolithic integration with semiconductor switches is full of interesting perspectives . The proposed architecture consists of two CMUTs layered on each side of a silicon substrate. A computational tool was designed to predict the behaviour of the transformer. Measurement protocols of the power efficiency of the constructed transformers were set up and allowed to quantify the prototypes' performances (A 32 % efficiency is currently reached, with improvements attainable up to 60 %). Exploring the results of the developed model, validated by bench measurements, allowed to determine the current limits of the transformers as well as perspectives of improvement

Modern high-strength but environmentally friendly, fuel-efficient and weight-optimized designs vital to the aeronautical and transport industries have resulted in the multi-material concept in which a wide range of materials are employed to exploit the various desirable mechanical and physical properties. These multi-material design concepts are susceptible to corrosion as the chemical and electrochemical properties of their constituent materials can vary widely. Since current corrosion mitigation strategies are not focused on these multi-material systems, there is an urgent need to understand the mechanism of the corrosion processes operative in these multi-material assemblies and develop suitable multi-material corrosion mitigation solutions in tandem with the increasing design trend towards multi-material structures. This work has focused on understanding the mechanism of multi-material corrosion in two multi-material systems that are of relevance to the aeronautical and transport industries; Al - Cu - CFRP (carbon fiber reinforced polymers) and Zn - Fe - CFRP galvanic systems respectively. On the basis of the insights obtained, appropriate multi-material corrosion mitigation options using inhibitors are to be identified and verified at the laboratory scale. The thesis objectives have been pursued by an incremental escalation technique in which the five individual materials constituting the two multi-material galvanic systems were first studied at the macro-scale in quiescent 50 mM NaCl solutions with and without inhibitors. Particularly, CFRP the only non-metallic material used was extensively studied with a view to understanding its deleterious electrochemical action as an efficient cathode when coupled to metals and how to mitigate it. Next technologically relevant dual material couples most relevant to the two galvanic systems were studied at the macro- and micro-scales, on the premise that inhibitors efficient at mitigating galvanic corrosion in these simpler components (Al - CFRP, Al - Cu, and Cu - CFRP for the Al - Cu - CFRP galvanic system) and (Fe - CFRP, Zn - CFRP, and Zn - Fe for the Zn - Fe - CFRP galvanic system) are prone to be effective for an entire multi-material system. Finally, promising inhibitors identified from dual material galvanic studies are tested on the multi-material combinations leading to identification of efficient multi-material corrosion inhibitors for both the Al - Cu - CFRP and Zn - Fe - CFRP multi-material combinations. The results demonstrate better understanding of the electrochemical behaviour of CFRP under cathodic polarization on galvanic coupling with metals and potential strategies to suppressing its ability to support cathodic reactions, and successful identification of potential inhibitors for mitigating multi-material corrosion in both systems. On the basis of results obtained in this work a scheme for monitoring degradation of CFRP was postulated as well as plausible mechanism(s) of multi-material corrosion and multi-material corrosion inhibition in Al - Cu - CFRP and Zn - Fe - CFRP multi-material galvanic systems, respectively
Os projectos mais recentes de veículos usados pelas indústrias aeronáutica e dos transportes combinam alta resistência, baixo peso, consumo eficiente de combustível e reduzido impacto ambiental, para o que juntam no mesmo desenho materiais muito diversos. A corrosão destas combinações multi-materiais pode ser acelerada quando se unem materiais com propriedades químicas e electroquímicas bastante diferentes. Como as estratégias actuais de mitigação da corrosão não focam sistemas multi-materiais, há a necessidade urgente em caracterizar os mecanismos da corrosão nestes novos sistemas a fim de desenvolver soluções eficazes para a sua prevenção. Este trabalho centrou-se na compreensão dos mecanismos da corrosão de dois sistemas multimateriais com relevância para as indústrias aeronáutica e dos transportes: Al - Cu - CFRP (polímeros reforçado com fibra de carbono) e Zn - Fe - CFRP, respectivamente. Com base nos resultados obtidos procurou-se identificar, à escala laboratorial, inibidores de corrosão eficazes. Começou-se por estudar separadamente cada um dos cinco materiais constituintes das combinações multi-materiais, em solução aquosa NaCl 50 mM com e sem inibidores de corrosão. O CFRP, o único material não metálico, foi estudado extensivamente para caracterizar a sua acção electroquímica como cátodo, pois esta torna-se prejudicial quando o CFRP está ligado a metais. Estudou-se também formas de minimizar a reacção catódica no CFRP e a corrosão dos outros metais. O passo seguinte foi o estudo de pares desses materiais à micro e macro-escala admitindo que os inibidores de corrosão capazes de reduzir a corrosão galvânica nestes sistemas simples (Al - CFRP, Al - Cu, e Cu - CFRP para o sistema galvânico Al - Cu - CFRP) e (Fe - CFRP, Zn - CFRP, e Zn - Fe para o sistema Zn - Fe - CFRP) serão também eficazes na protecção da estrutura multi-material real. Por fim os inibidores mais eficientes foram estados para as combinações multi-marieriais completas, Al - Cu - CFRP e Zn - Fe - CFRP. Os resultados obtidos trazem uma melhor compreensão do comportamento electroquímico do CFRP quando sujeito a polarização catódica ou quando ligado galvanicamente a vários metais. Os resultados apresentam também estratégias possíveis para impedir o processo catódico à superfície do CFRP. Identificou-se ainda vários compostos com a capacidade de inibir a corrosão nos sistemas Al - Cu - CFRP e Zn - Fe - CFRP. Como resultado do trabalho realizado para esta Tese, desenvolveu-se um procedimento para monitorização da degradação do “plástico” reforçado com fibra de carbono (CFRP). Propõem-se também mecanismos para a corrosão e inibição em sistemas multi-material como por exemplo, Al - Cu - CFRP e Zn - Fe - CFRP
Programa Doutoral em Ciência e Engenharia de Materiais

碩士
國立海洋大學
河海工程學系
82
In this study, the inhibit efficiency and mechanical properties of two inhibitors in concrete are evaluated. Two kind of inhibitors (0.05% to 0.5% by weight of dry cement), potassium chromate and sodium sulfite, are added in concrete. To simulate the chemistry of the contaminated concrete in marine environment, NaCl (0.5%) by weight of dry cements is added in some specimens. After 28-days water curing, specimens are divided into two groups：the firstgroup is immersed in sea water to simulate the nature corrosion process, and the second group is immersed in sea water and connected to DC power supply to accelerate the corrosion process. The open circuit potential (OCP) and AC impedance methods are employed to evaluate the inhibit efficiency, and the compressive strength test and pull-out test are applied to study the degradation of mechanical behaviors due to inhibitors. The results show that potassium chromate is a better inhibitor than sodium sulfite. The compressive strength is reduced while these two inhibitors areused in concrete. On the other hand, bond strength do not change sosignificant for potassium chromate. The OCP and AC impedance methods show that potassium chromate do inhibit corrosion of steel rebars if sufficient amount is added. In accelerated experiments, it was surprisingly found that some specimens of the potassium chromate group show positive OCPs.

Reinforced concrete (RC) structures comprise a large part of the structures and infrastructures around the world. Most of them have been built in the first half of the 20th-century, so their service life is currently at a critical stage from the maintenance perspective. One of the most frequent and expensive degradation mechanisms they present is associated with the reinforcement corrosion. This research is focused on the carbonation-induced corrosion considering that it is the primary degradation cause of RC structures in Paraguay. The growing problem of climate change has caught the attention of maintenance managers of these structures since the end of the last century. Several studies shown that structures can be affected by the impact of this phenomenon considering its durability highlighting the reduction of its expected service life caused by an increase in the corrosion rate associated with the rise in temperature and the atmospheric concentrations of CO2. These conclusions led to the development of this thesis whose main objective is to develop an optimised methodology for the formulation of maintenance strategies of RC structures subjected to the carbonation-induced corrosion, considering the effects of climate change. For the fulfilment of the objectives of this thesis, an analysis has been developed on the numerical modelling of carbonation in RC structures to obtain the degradation curves. The degradation curves obtained by the chosen and modified model show the expected carbonation depth in Paraguay for the next 50 years under the consideration of different climate scenarios. With this analysis, it was possible to determine the corrosion initiation and corrosion propagation times for the structures considering several configurations of the principal parameters influencing durability: the quality of the concrete and the cover thickness. Once the degradation conditions were defined, preventive maintenance strategies based on decision models were formulated. These numerical models were established in two stages comprising the inspections and the repairs planning. For the inspections planning, an efficiency analysis was proposed that is complemented by the optimisation process of the inspection schedule and the most appropriate intervention techniques. For the repairs planning, a dynamic model for decision-making has been developed which considers the cost analysis of the maintenance strategy and the capabilities of the inspection and repair techniques to effectively ensure the durability of the structures through the preventive maintenance approach. The main results of this thesis shown that the carbonation-induced corrosion risk of structures can increase in the future due to the climate change effect. Thus, for the worst climate scenario, in the second half of this century is expected an increase by 25% in the maximum carbonation depth regarding a control scenario. Meanwhile, the time to reach the same maximum carbonation depth of the control scenario can be reduced between 7 and 10 years for the best climate scenario, depending on the quality of the concrete. Furthermore, the maintenance model developed in this research is easily applicable and allows the formulation of long-term strategies that optimise resources at the lowest cost to deal with this degradation mechanism.
As estruturas de betão armado (BA) constituem uma grande parte das estruturas e infraestruturas construídas em todo o mundo. A sua maioria foi construída na primeira metade do século passado, logo, a sua vida útil apresenta atualmente, em muitos casos, um estado crítico, na perspetiva da sua manutenção. Um dos mecanismos de degradação mais frequentes e dispendiosos neste tipo de estruturas está associado à corrosão das armaduras. Esta tese analisa a corrosão induzida por carbonatação, considerando que é a principal causa de degradação em estruturas de betão no Paraguai. O problema crescente advindo das alterações climáticas alertou os responsáveis da manutenção deste tipo de estruturas, desde o final do século passado. Vários estudos mostraram que podem ser afetadas pelo impacto desse fenômeno no que respeita à sua durabilidade, salientando a redução na expectativa de vida útil dessas estruturas, causada por um aumento da taxa de corrosão, associada ao aumento da temperatura e às concentrações atmosféricas de CO2. Estas conclusões levaram ao desenvolvimento desta tese, cujo objetivo principal é desenvolver uma metodologia otimizada para a formulação de estratégias de manutenção de estruturas de BA submetidas à degradação por corrosão induzida por carbonatação, considerando os efeitos das alterações climáticas. Para o cumprimento dos objetivos desta tese, efetuou-se uma análise de modelos numéricos de carbonatação em estruturas de betão armado, para a obtenção das curvas de degradação. As curvas de degradação obtidas com o modelo matemático escolhido e modificado, mostram a profundidade de carbonação esperada no Paraguai para os próximos 50 anos, considerando diferentes cenários climáticos. Por sua vez, com esta análise, foi possível determinar os tempos de início e de propagação da corrosão previstos para as estruturas, considerando diversas configurações dos principais parâmetros que influenciam a durabilidade: a qualidade do betão e a espessura do recobrimento. Definidas as condições de degradação foram formuladas estratégias de manutenção preventiva baseadas em modelos de decisão. Estes modelos numéricos foram estabelecidos em duas etapas que compreendem o planeamento das inspeções e o planeamento das reparações. Para a primeira etapa foi proposta uma análise de eficiência, complementada com o processo de otimização dos momentos de inspeção e das técnicas de intervenção mais apropriadas. Para o planeamento da reparação, foi desenvolvido um modelo dinâmico para apoio à tomada de decisões que considera a análise de custos da estratégia de manutenção e a capacidade das técnicas de inspeção e reparação para garantir a durabilidade das estruturas, de forma eficaz, através de manutenção preventiva. Os resultados desta tese mostram que o risco de degradação de estruturas de betão armado induzidas por carbonatação, pode aumentar no futuro devido ao efeito das alterações climáticas. Assim, para o pior cenário climático, estima-se um aumento médio de 25% na profundidade máxima de carbonação na segunda metade deste século em relação a um cenário de controle. Enquanto que o tempo para atingir a mesma profundidade máxima de carbonatação do cenário de controle pode ser reduzido entre 7 e 10 anos para o melhor cenário, dependendo da qualidade do betão. Além disso, o modelo de manutenção desenvolvido é facilmente aplicável e permite a formulação de estratégias de longo prazo que otimizem recursos ao menor custo, para lidar com esse mecanismo de degradação.
Las estructuras de hormigón armado (H°A°) comprenden una gran parte de las infraestructuras en todo el mundo. La mayoría de estas estructuras se han construido en la primera mitad del Siglo XX, por lo que su vida útil se encuentra actualmente en una etapa crítica desde la perspectiva del mantenimiento. Uno de los mecanismos de degradación más frecuentes y costosos en este tipo de infraestructura está asociado con la corrosión del refuerzo. Esta investigación se centra en la corrosión inducida por la carbonatación, ya que es la principal causa de degradación de las estructuras de H°A° en Paraguay. El creciente problema del cambio climático ha llamado la atención de los administradores del mantenimiento de las estructuras desde finales del siglo pasado. Varios estudios han demostrado que las infraestructuras podrían verse afectadas por el impacto de este fenómeno desde el punto de vista de la durabilidad. Estos estudios han demostrado una reducción en la vida útil prevista de las estructuras causada por un aumento en la tasa de corrosión asociada con el aumento de temperatura y las concentraciones atmosféricas de CO2. Esta condición ha llevado a la elaboración de esta tesis cuyo principal objetivo es desarrollar una metodología optimizada para la formulación de estrategias correspondientes al mantenimiento de estructuras H°A° sometidas a la corrosión inducida por la carbonatación, considerando los efectos del cambio climático. Para el cumplimiento de los objetivos de esta tesis, se ha desarrollado un análisis sobre la modelación numérica de la carbonatación en el hormigón para obtener las curvas de degradación en estas estructuras. Estas curvas muestran la profundidad de carbonatación esperada en Paraguay durante los próximos 50 años bajo la consideración de diferentes escenarios climáticos. A su vez, con este análisis se ha podido determinar el tiempo de inicio y propagación de la corrosión previstos para las estructuras considerando varias configuraciones de los parámetros principales para la durabilidad: la calidad del hormigón y el espesor del recubrimiento. Una vez que se han definido las condiciones de degradación, se han formulado estrategias de mantenimiento preventivo basadas en modelos de decisión. Estos modelos numéricos se han establecido en dos etapas que comprenden la planificación de inspecciones y la planificación de reparaciones. Para la planificación de las inspecciones, se ha propuesto un análisis de eficiencia que se complementa con el proceso de optimización de los tiempos de inspección y las técnicas de intervención más adecuadas. Para la planificación de reparaciones, se ha desarrollado un modelo dinámico para la toma de decisiones que considera el análisis de costos de la estrategia de mantenimiento y las capacidades de las técnicas de inspección y reparación para garantizar la durabilidad de las infraestructuras de manera efectiva a través del enfoque de mantenimiento preventivo. Los resultados de esta tesis han demostrado que el riesgo de corrosión inducida por la carbonatación de las estructuras podría aumentar en el futuro debido al efecto del cambio climático. Así, para el peor escenario climático, podría esperarse un aumento medio de 25% de la profundidad máxima de carbonatación en la segunda mitad de este siglo respecto a un escenario de control. Mientras tanto, el tiempo para alcanzar la misma profundidad máxima de carbonatación del escenario de control podría reducirse entre 7 y 10 años para el mejor escenario climático, dependiendo de la calidad del hormigón. Además, el modelo de mantenimiento desarrollado en esta investigación es fácilmente aplicable y permite la formulación de estrategias a largo plazo que optimizan los recursos al menor costo para hacer frente a este mecanismo de degradación.
This research has been funded with the support of the European Commission. This publication reflects the view only of the author, and the Commission cannot be held responsible for any use, which may be made of the information contained therein - ELARCH program (Project Reference number: 552129-EM-1-2014-1-IT-ERA MUNDUS-EMA21)
Programa Doutoral em Engenharia Civil

Proprietary mixtures of amines and carboxylic acids are used as volatile corrosion inhibitors (VCIs) for the protection of steel and iron components against atmospheric corrosion during storage and transportation. Interactions between amines and carboxylic acids have been comprehensively reported in the literature. However, little is known about the nature of the vapours these mixtures emit. The present study focused on the development of the evolved gas analysis method which will help in the characterisation of the vapours released by VCIs. In the method, the evaporation of various amine-carboxylic acid binary mixtures was monitored by thermogravimetric analysis (TGA). The nature and the composition of the released vapours was followed by Fourier transform infrared (FTIR) spectroscopy. Mixtures consisting of triethylamine (TEA) and acetic acid were studied as a model compound using TGA-FTIR at 50 °C to validate the TGA-FTIR method. As vaporisation progressed, the composition of the remaining liquid and the emitted vapour converged to a fixed amine content of ca. 27 mol %. This is just above the composition expected for the 1:3 amine: carboxylic acid complex. Mixtures close to this composition also featured the lowest volatility. TGA-FTIR proved to be a convenient method for studying the evaporation of TEA-acetic acid mixtures, and the nature and composition of the released vapours. Amine addition leads to the dissociation of carboxylic acid dimers in favour salt formation. The formation of an ion pair between the amine and carboxylic acid was confirmed by the FTIR spectra of the liquid phase. The resulting amine-carboxylic acid mixtures showed a slow mass loss rate on TGA when compared with the pure amines and pure carboxylic acids. This indicated that the mixtures have low volatility, hence low vapour pressure compared with the pure components. The low vapour pressure of the mixtures was confirmed by the calculated gas permeability values. These values were much higher for the pure amines and the pure carboxylic acids. However, they dropped significantly on amine addition. The strong amine-carboxylic acid interaction is responsible for the suppressed volatility of the mixtures. No interaction is observed between amine and carboxylic acid molecules in the vapour phase at 230 °C. The method developed was applied to characterise the model compounds simulating the amine-carboxylic acid-based volatile corrosion inhibitors. These model systems contained the primary, secondary and tertiary amines (hexylamine, morpholine and triethylamine), as well as carboxylic acids with different chain lengths (acetic, propanoic, hexanoic and octanoic). These systems are usually employed as equimolar mixtures to protect ferrous metals against atmospheric corrosion. The key finding of the study was that the vapours released by such equimolar mixtures initially contain almost exclusively free amine. After prolonged vaporisation, a steady-state “azeotrope”-like composition is approached. It contains excess acid and features impaired corrosion-inhibition efficiencies according to the Skinner test. In part, this behaviour can be attributed to the mismatch between the volatilities of the amine and carboxylic acid constituents.
Thesis (PhD)--University of Pretoria, 2013.
gm2013
Chemical Engineering
unrestricted

Tese de Doutoramento em Ciência (área de especialização em Química).
A corrosão de armaduras no betão armado, por carbonatação do betão ou ataque por iões cloreto, é uma das maiores causas de degradação de estruturas. A propagação da corrosão após o seu início é, em geral, rápida, podendo conduzir à deterioração das estruturas num curto espaço de tempo, com custos de reparação elevados. A utilização do aço galvanizado é reconhecida como uma medida alternativa para aumentar o tempo de vida útil das estruturas expostas ao ataque de espécies agressivas. Imediatamente após embeber o aço galvanizado no betão fresco, que se revela como um ambiente extremamente alcalino, a camada de zinco corrói-se durante um certo período (podendo variar de apenas umas horas a alguns dias) até que a camada de passivação se forme e o betão conclua o processo de cura. Este processo de corrosão inicial pode levar a um consumo da camada de zinco que varia entre 5 e 10 μm. Simultaneamente, ocorre produção de hidrogénio que pode originar perda de aderência entre o aço de reforço e o betão. Para minimizar e/ou bloquear esta reacção inicial, usam-se vários procedimentos tais como o aumento do teor de cromatos no cimento ou aquando da preparação do betão, a adição de água com cromatos dissolvidos. Adicionalmente, a deposição de camadas de conversão química à base de crómio na superfíce do aço galvanizado também foi um método amplamente utilizado. Consequentemente, este tipo de medidas tornaram-se rotina na prevenção da evolução do hidrogénio e proteção das armaduras galvanizadas. No entanto, devido à toxicidade dos iões Cr(VI), os cimentos Portland actualmente comercializados possuem na sua composição quantidades reduzidas de Cr(VI) e a aplicação de camadas de conversão química à base de crómio tem vindo a ser evitada. O método sol-gel é um processo versátil que envolve a utilização de uma ampla diversidade de precursores permitindo a incorporação de componentes adicionais que introduzem funcionalidades complementares tais como resistência à humidade, aderência, proteção da corrosão juntamente com o aumento das propriedades mecânicas, térmicas e ópticas. As vantagens deste processo são numerosas e além dos componentes orgânicos outros aditivos como os inibidores podem ser incorporados no sistema sol-gel melhorando a resistência à corrosão dos substratos metálicos. O presente estudo enquadra-se no desenvolvimento de revestimentos híbridos “amigos” do ambiente produzidos pelo método sol-gel para aço galvanizado de modo a minimizar a corrosão do zinco e a evolução de hidrogénio quando em contacto com meios cimentícios. Os pré-tratamentos propostos representam alternativas viáveis na substituição de pré-tratamentos à base de Cr(VI) utilizados para controlar a reação inicial entre o zinco e o betão fresco. Sintetizaram-se matrizes híbridas, baseadas em ureiasilicatos e aminoálcool-silicatos, que foram testadas na sua forma pura e após dopadas com um agente inibidor (Cr(III)). Os revestimentos foram depositados no aço galvanizado pelo método dip-coating. A eficiência dos diferentes híbridos enquanto barreira de protecção, em contacto com materiais que mimetizam as propriedades físico-químicas do betão (pastas cimentícias e argamassas) foi estudada e avaliada por diversas técnicas eletroquímicas e por técnicas de análise de superfície. Os resultados evidenciaram que os revestimentos híbridos obtidos pelo método sol-gel possuem propriedades promissoras para serem utilizados como pré-tratamentos “amigos” do ambiente no aço galvanizado em contacto com meios cimentícios. Os revestimentos estudados permitem, efetivamente, mitigar os efeitos adversos das reações iniciais entre o aço galvanizado e os materiais cimentícios. Estes pré-tratamentos revelaram-se alternativas promissoras à utilização de camadas químicas de conversão baseadas em cromatos.
The corrosion of steel in concrete is one of the major causes of structures degradation, requiring expensive rehabilitation. The use of hot dip galvanized steel (HDGS) has been recognized as an effective measure to increase the service life of reinforced concrete structures exposed to carbonation or to chloride ions. Immediately after the HDGS is embedded in fresh concrete, a highly alkaline environment, the zinc coating corrodes for a limited period (from several hours to a few days) until passivating surface layers are formed and the concrete hardens. This initial corrosion process may lead to zinc consumption between 5 to 10 μm. At the same time, hydrogen is produced which may lead to the loss of adherence between the steel and the concrete. Common procedures such as increasing the chromate content of the cement or adding water-soluble chromates into this preparation and the use of chromate conversion coatings (CCC) has a favourable effect on blocking initial zinc corrosion. Consequently, these have been trivial procedures employed to prevent hydrogen gas evolution and to protect the hot-dip galvanized rebars. However, due to the toxicity of Cr(VI) ions, current commercialized Portland cements have limited the content of Cr(VI) in their composition and the use of CCCs are currently being avoided. The sol–gel method is a versatile process involving the use of a large diversity of precursors, allowing the incorporation of additional components. This introduce complementary functionalities of the material, such as moisture resistance, adhesion and corrosion protection, along with the enhancement of mechanical, thermal and optical properties. The advantages of this technology are numerous and besides the organic component, other additives, such as inhibitors could be incorporated into the sol– gel system increasing the corrosion resistance of the metal substrates. This study is focused on the development of OIH coatings for HDGS reinforcement in contact with cementitious media. OIH sol-gel matrices doped and undoped with inhibitors, ureasilicate and alcoholaminosilicate, were synthesized. The coatings were deposited on HDGS by a dipping process. The barrier efficiency of the different OIH sol-gel coatings was studied and assessed by several electrochemical techniques and surface analysis, when in contact with cementitious materials (cement pastes and mortar). The results show that the OIH sol-gel coatings studied effectively allow the mitigation of harmful effects of the initial excessive reaction between cementitious materials and the HDGS, showing promising properties to be used as eco-friendly pre-treatments on HDGS in contact with cementitious media.
Fundação para a Ciência e Tecnologia (FCT) for the PhD grant SFRH/BD/62601/2009.
Centro de Química [project F-COMP-01-0124-FEDER-022716 (ref. FCT PEst-C/QUI/UI0686/2011)-FEDER-COMPETE].