Un nouveau procédé, basé sur une adaptation innovante du principe de protection cathodique des ouvrages métalliques en milieu marin, consiste à favoriser la précipitation d’un agglomérat calcomagnésien sur plusieurs centimètres d’épaisseur. En présence de sable et de coquillages, cet agglomérat pourrait permettre de stabiliser des zones littorales en cours d’érosion ou d’améliorer l’ancrage d’enrochements brise-lames. L’objectif de ce travail est d’étudier et de comprendre les mécanismes réactionnels de formation de cet agglomérat permettant une précipitation en volume loin de la cathode afin d’en optimiser la vitesse de formation ainsi que ses propriétés mécaniques. Premièrement, il a été montré dans ces travaux que le milieu électrolytique pouvait influer sur la croissance du dépôt, avec une possible inhibition de formation de carbonate de calcium pour les faibles potentiels. L’influence des produits de corrosion dans le mécanisme de protection cathodique a également été mise en évidence grâce à des polarisations effectuées dans NaCl, eau de mer artificielle et naturelle. Deuxièmement, des essais d’un mois en courant imposé ont été menés du laboratoire jusqu’au site naturel, afin de se rapprocher des conditions réelles. La densité de courant appliquée ainsi que les conditions hydrodynamiques sont des facteurs clefs étroitement liés l’un à l’autre, influant sur la masse et le rapport Ca/Mg. Ces travaux ont aussi permis de mettre en avant l’influence du temps de polarisation sur la composition du dépôt calcomagnésien, présentant une cinétique de croissance stable mais une fluctuation de composition après 15, 30 et 60 jours. Cette variation interne du rapport Ca/Mg, attribuée à un processus de « dissolution/précipitation » dépendant du gradient de pH, ainsi que la répartition de ces éléments au sein du dépôt pourraient jouer un rôle majeur dans l’évolution de la tenue mécanique du dépôt au cours du temps. / A new method, based on an innovative adaptation of cathodic protection principle of metal structures in marine environment, is to promote the precipitation of a calcareous agglomerate several centimeters thick. In the presence of sand and shells, this cluster could stabilize coastal areas being eroded or improve anchorage of breakwater riprap. The objective of this work is to study and understand the reaction mechanisms allowing to create a voluminous calcareous deposit away from the cathode and to optimize deposition time as well as its mechanical properties. First, it was shown in this work that the electrolytic medium could affect the growth of the deposit, with a possible inhibition of formation of calcium carbonate fot the low potential. The influence of corrosion products in the cathodic protection mechanism was also highlighted through polarizations performed in NaCl, artificial and natural sea water. Second, one month test with impressed current were conducted from laboratory to natural site, in order to get closer of real conditions. Current density and hydrodynamic conditions are key factors closely bonded to each other, affecting the mass and composition of the Ca/Mg ratio. This work has also helped to highlight the influence of the polarization time on the composition, with stable growth kinetics but a composition’s evolution after 15, 30 and 60 days. This internal variation of the Ca/Mg ratio attributed to a process of « dissolution/precipitation » is pH dependent and the distribution of these elements within the deposit could play a major role in the evolution of the mechanical strength of deposit over time.

La protection cathodique par courant imposé (PCCI) est l’une des techniques adoptées pour limiter ou annihiler la corrosion dans le béton armé. Le but de cette thèse est de développer des revêtements suffisamment conducteurs et autonomes pour s’affranchir de l’utilisation des anodes primaires métalliques lors de la PCCI. Ce mémoire est formé de quatre parties principales :I. La première partie résume la recherche bibliographique réalisée. II. Cette partie sera consacrée à la formulation des revêtements électro-conducteurs par dispersion des poudres-pigmentaires conductrices (métallique ou carbone) dans une résine acrylique ou polyuréthane. III. L’efficacité des revêtements électro-conducteurs en tant qu’anode autonome est étudiée dans cette partie. IV. La dernière partie présente des essais de PCCI réalisés en continu pendant 6 mois sur des dallettes corrodées. Des spécimens témoins non corrodés sont aussi placés dans le même environnement sans protection cathodique. / Impressed Current Cathodic Protection (ICPP) is one of the electrochemical techniques applied to limit or annihilate corrosion. The aim of this thesis is to develop sufficiently conductive and autonomous coatings to overcome the use of primary anodes during ICPP. This thesis is based on four main parts:I. The first part summarizes a bibliographic review of corrosion in reinforced concrete. II. This part will focus on the formulation of electroconductive coatings by mixing conductive powders (metallic or carbon) with an acrylic or polyurethane resin. III. The effectiveness of electroconductive coatings as an autonomous anode is studied in this section. IV. The last part presents ICCP tests carried out continuously for 6 months on corroded slabs. Non-corroded specimens are also placed in the same environment without cathodic protection in order to make a comparative analysis.

Through history, iron has mainly been used as reinforcement in concrete. Contemporary building technology would not have been possible without reinforced concrete, however, from a global perspective, many concrete buildings have begun to encounter reinforcement corrosion, mainly due to chlorides and carbonation. When the chlorides come into contact with the reinforcing bars, a chemical reaction begins, which causes the iron to oxidize and begin to corrode. In a humid environment when the reinforcement corrodes, the iron expands and bursts the concrete from inside, which in turn results in cracks occurring in the concrete structure. In an environment with lack of oxygen, it often occurs that non expanding rust products form that are not defected on the concrete surface occurs through discoloring or spalling. This type of damage is not detected ocularly and therefore forms a more serious type of injury. This type of rust is a silent type of damage that can cause deteriorated bearing capacity in the construction, since the cross-sectional area of the reinforcement in the concrete decreases. Sweco has been involved in a couple of projects where there have been huge problems due to corrosion of reinforcement. The damages that emerged leading to the repairs of these type of damage costing large sums. This report is based on previous projects, articles, literature studies, reports and interviews. Interviews have been conducted with competent people who have shared their valuable opinions, knowledge and experiences. In order to stop ongoing corrosion of reinforcement and also repair the damage, several alternative solution and repair measures have been devolped. Some of the most relevant suggestions in this report is to remove the damaged concrete and then re-cast or alternatively cast in cathodic protection or a combination of these. / Genom historien har man främst använt sig av järn som armering i betong. Samtidens byggteknik hade inte varit möjlig utan armerad betong, dock behöver man vara uppmärksam på armeringskorrosion framför allt på grund av klorider och karbonatisering. När kloriderna kommer i kontakt med armeringsjärnen påbörjas en kemisk reaktion som leder till att järnen oxiderar och börjar korrodera. I fuktig miljö när armeringen korroderar, expanderar järnen och spränger betongen inifrån vilket i sin tur resulterar i att sprickor uppstår i betongkonstruktionen. I syrefattiga miljöer uppstår det oftast svartrost som är den typ av skada som uppstår inuti en betongkonstruktion. Denna typ av skada upptäcks inte okulärt och blir därför en allvarligare typ av skada. Svartrost är även den typ av skada som kan förorsaka försämrad bärighet i konstruktionen eftersom tvärsnittsarean hos armeringen i betongen minskar. Sweco har varit inblandade i ett par projekt där det har förekommit enorma problem på grund av armeringskorrosion. Skadorna som har uppstått på grund av armeringskorrosion har lett till att reparationerna av dessa skador har varit kostsamma. Denna rapport är baserad på tidigare projekt, artiklar, litteraturstudier, rapporter samt intervjuer. Intervjuer har genomförts med kompetenta personer som har delat med sig av sina värdefulla åsikter, kunskaper och erfarenheter för att få en bättre uppfattning av konsekvenserna som uppstår på grund av armeringskorrosion. För att stoppa pågående armeringskorrosion och även reparera skadorna, har reparationsåtgärder i denna rapport tagits fram. Några utav de mest relevanta förslag på åtgärder i denna rapport är att ta bort den skadade betongen för att sedan gjuta på nytt, alternativt gjuta in katodiskt skydd eller en kombination av dessa.

[pt] A corrosão é a patologia mais recorrente no concreto armado, responsável por custos elevados na recuperação das estruturas afetadas. Além dos custos diretos como os materiais utilizados na recuperação, a mão de obra especializada, substituição de peças ou equipamentos afetados, existem os custos indiretos como a paralização da utilização da estrutura, mobilização de moradores em caso de edificações residenciais, perda de produção em caso de edificação industriais, entre outros. Encontrar e apresentar meios para o combate e a prevenção da corrosão é de extrema importância. A proteção catódica tem se apresentado nas últimas décadas como uma forma eficaz de combate a corrosão, não só paralisando o processo corrosivo totalmente, mas também prevenindo o surgimento de novos pontos. Seu uso vem sendo aplicado cada vez mais em estruturas de concreto armado, como pontes, cais, edifícios industriais e residenciais e túneis. Diversos materiais vêm sendo testados e aprovados, possibilitando a flexibilização e a adaptação do melhor sistema para cada estrutura. Relatos de casos com uso da proteção catódica tem mostrado a sua eficácia mesmo depois de anos de instalação. Essa dissertação apresenta a proteção catódica, seus sistemas de uso, casos em que foi instalada, um experimento com proteção catódica por corrente impressa para a restauração de uma ferramenta de aço, além de um modelo computacional desenvolvido para o dimensionamento de anodos galvânicos para estruturas de concreto armado. / [en] Corrosion is the most recurrent pathology in reinforced concrete, responsible for high costs in the recovery of affected structures. In addition to direct costs such as materials used in the recovery, specialized labor, replacement of affected parts or equipment, there are indirect costs such as the interruption of use of the structure, mobilization of residents in case of residential buildings, loss of production in case of industrial buildings, among others. Finding and introducing means to combat and prevent corrosion is extremely important. Cathodic protection has been presented in the last decades as an effective way to combat the corrosion, as it not only paralyzes the corrosive process completely, but also preventing the combat to new points. Its use has been increasingly applied in structures such as bridges, industrial and residential buildings, and tunnels. Various materials have been tested and approved, adaptation system for flexibility and adaptation to better each structure. Case reports with the use of cathodic protection have had attention even after years of installation. This dissertation presents cathodic protection, its systems of use, cases in which it was installed, an experiment with cathodic protection by impressed current for the restoration of a steel tool, as well as a computational model developed for the design of galvanic anodes for reinforced concrete structures.

Galvanic anode technology has in recent years come to the fore as a cost-effective method of successfully mitigating the corrosion of reinforcing steel in concrete structures. Developments in the field of cathodic protection have included the introduction of a novel Hybrid anode system, which uses the same sacrificial anode to pass a short-term impressed current before being connected to the steel directly to provide a long-term galvanic current. Galvanic and hybrid technologies are often seen as less powerful solutions in the treatment of reinforcement corrosion, and the test methodologies which determine the efficacy of cathodic protection systems favour impressed current technologies. The work completed has investigated the application of traditional and novel corrosion assessment techniques to laboratory samples to assess the protection offered by the hybrid treatment methodology in both treatment phases. In addition, the response of both galvanic and hybrid anodes to environmental conditions has been recorded and assessed before being discussed in the context of steel protection criteria. Finally, an investigation is presented into the on-site deterioration of commercially pure titanium feeder wire installed as part of the hybrid anode system and potential solutions to the problem have been documented. The research undertaken found that the hybrid anode system is capable of protecting steel in challenging, aggressive environments. This was confirmed by steel corrosion rate and indicative steel potential measurements. The responsive behaviour investigation showed that the current output of galvanic and hybrid anodes responds rapidly to changes in the corrosion risk posed to the steel and that this has a direct effect on anode system lifetimes. An assessment of the polarisation-based protection criteria applied to steel in concrete has found that the standard inhibits the use of responsive behaviour, and that revisions which consider the present risk of steel corrosion by considering the corrosion current resulting from the relative aggressivity of the concrete environment would be more valid in their application. A cathodic protection system based on the concepts of pit re-alkalisation and pH maintenance can fully utilise galvanic anode responsive behaviour. It was discovered that the deterioration of commercially pure titanium feeder wire seen on site installations was due to anodising in the presence of chloride media which had the potential to lead to pitting corrosion. The pitting risk varied depending on the duration of the treatment and proximity to the installed anode. An anodically grown oxide delayed the onset of corrosion in aqueous KBr solution, but did not significantly increase the pitting potential.

No description available.

De nouveaux alliages Zn-TR1-5 %mass.(TR = Ce, La et Mischmetal : Ce 75%/La25%) ont été synthétisés par fusion sous atmosphère contrôlée et coulés sous forme de plaques. Dans ces nouveaux matériaux, les terre rare sont localisées exclusivement dans des phases intermétalliques dispersées de manière homogène dans la matrice de zinc : Zn11Ce, Zn13La ou Zn11Ce1-xLax and Zn13CeyLa1-y. Le comportement électrochimique de ces nouveaux alliages a été étudié dans un milieu corrosif de référence simulant les conditions atmosphériques. En parallèle, les phases intermétalliques pures Zn11Ce and Zn13La ont été synthétisées et leur influence électrochimique a été évaluée par voltamétrie et couplage galvanique. Les résultats montrent que les deux phases intermétalliques sont des sites cathodiques préférentiels de la réduction du dioxygène et induisent une inhibition cathodique de la corrosion des alliages Zn-TR par rapport au zinc pur. Ce phénomène est plus marqué dans le cas des alliages au lanthane. Dans le cas spécifique des alliages au cérium, une inhibition anodique a également été observée et corrélée avec une modification chimique des produits de corrosion (composés majoritairement d'hydrozincite). En fait, une faible quantitéhomogène de cérium a pu être mise en évidence dans la couche de corrosion par spectrométrie dispersive en longueur d'onde. D'après les résultats d'expériences de précipitation contrôlée de sels de cérium et zinc en milieu carbonaté, la présence de cérium dans la couche de corrosion et son caractère protecteur pourraient être attribués à la formation d'un composé mixte double lamellaire zinc-cérium. L'addition de moins de 2%mass. de cérium ou lanthane permet d'améliorer la résistance à la corrosion du zinc. Cependant, lorsque la teneur en terre-rare augmente, l'effet de couplage galvanique devient plus important et rend les alliages moins résistants que le zinc pur / New Zn-RE1-5 wt.% alloys (RE=Ce, La and Mischmetal: Ce 75%/ La 25%) were synthesized by melting under controlled atmosphere and cast in plates. In these materials, rare earth metal are exclusively present in intermetallic phases homogeneously dispersed in the zinc matrix: Zn11Ce, Zn13La or Zn11Ce1-xLax and Zn13CeyLa1-y. The electrochemical behavior of these new alloys was investigated in a reference corrosivemedium. In parallel, the pure intermetallic phases Zn11Ce and Zn13La were synthesized and their electrochemical influence was studied by voltametry and galvanic coupling. Results show that both intermetallic phases act as preferential cathodic sites of dioxygen reduction and induce a cathodic inhibition of the corrosion of the Zn-RE alloys by comparison with pure zinc. This phenomenon is much more significant in the case of lanthanum containing alloys. In the specific case of cerium addition to zinc, an anodic inhibition was also observed and correlated with a chemical modification of the corrosion products (mainly made of hydrozincite). Actually, low quantities of cerium (less than 1 at.%) have been detected homogeneously in the corrosion layer by wave-length dispersive spectrometry. From results of controlled precipitation experiments of cerium and zinc salts performed in carbonated medium, the presence of cerium in the corrosionlayer and its protective character could be attributed to the formation of a mixed double lamellar zinc-cerium product. Therefore, addition to zinc of less than 2 wt.% of cerium or lanthanum allow to improve the corrosion resistance of zinc. However, by increasing the rare earth content in the alloys, the galvanic coupling phenomenon becomes more important and makes the alloys less resistant than pure zinc

A polianilina é dos polímeros condutores mais estudados e com diversas aplicações, dentre elas o uso no recobrimento de aços para proteção à corrosão. Este trabalho objetivou encontrar as condições de eletrossíntese de polianilinas em meio aquoso neutro e a avaliação de proteção à corrosão, tendo como substrato o aço inox 304. As polianilinas eletrossintetizadas foram uma forma pura (PAni) e outra modificada com a adição de melamina (PAni/MM). Dentre as justificativas deste trabalho está a necessidade de aprofundar os escassos estudos em eletrossínteses em meio aquoso neutro. Neste trabalho, são apresentados as condições de eletrossíntese das polianilinas, a caracterização preliminar das polianilinas por UV-visível, FTIR e MEV, ensaios de polarização potenciodinâmica e impedância eletroquímica do aço inox 304 sem e com filmes das polianilinas para avaliar a resistência à corrosão em meio aquoso de NaCl 0,5 mol/L. O trabalho mostrou que a eletrossíntese das polianilinas em meio aquoso neutro é viável. Além disso, foi verificada a seguinte ordem do potencial de corrosão, do menor para o maior: aço inox 304 puro, aço inox 304 com PAni e aço inox 304 com PAni/MM. / Polyaniline is one of the most studied conducting polymers and with various applications, including use on steels for corrosion protection. This work aimed to find the conditions for electrosynthesis of polyanilines in neutral aqueous media and to evaluated the corrosion protection of 304 stainless steel. The electrosynthesizeds polyanilines were one pure form (PAni) and one with the addition of melamine (PAni/MM). One of the justifications of this work is the need to deepen the scarce studies in electrosynthesis in neutral aqueous media. In this work, we will see the conditions for electrosynthesis of polyanilines, the UV-visible, FTIR and SEM polyanilines preliminary characterization, the potentiodynamic polarization experiments and impedance spectroscopy of 304 stainless steel without and with films from polyanilines for evaluate the corrosion resistance in NaCl 0,5 mol/L aqueous media. This work showed that electrosynthesis of polyanilines is feasible in neutral aqueous media. In addition, it was verified the following order of corrosion potencial, from lowest to highest: pure 304 stainless steel, 304 stainless steel with PAni and 304 stainless with PAni/MM.

FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / A fragilização por hidrogênio tem sido um problema constante em diferentes setores da indústria. Por ser o menor átomo existente, o hidrogênio difunde-se na microestrutura dos materiais metálicos, inserindo tensões mecânicas internas que podem, eventualmente, levar a uma falha catastrófica. Atualmente, os métodos mais comuns existentes para analisar este fenômeno são lentos e caros, configurando-se assim a necessidade de desenvolver um método de ensaio que não possua tais desvantagens. No presente trabalho, apresenta-se o desenvolvimento de um equipamento cuja função é avaliar de forma rápida a susceptibilidade à fragilização por hidrogênio (SFH) dos materiais metálicos através de ensaios de carregamento progressivo em meio assistido (RSL). Este equipamento apresenta uma grande vantagem em relação aos outros métodos avaliação da SFH, que é o menor tempo de ensaio para se ter resultados representativos. Na presente dissertação foram realizadas a concepção, projeto, simulação em elementos finitos, construção e validação do equipamento. Sua validação foi realizada ensaiando-se uma amostra sem entalhe,cuja tensão mecânica medida foi comparada com aquela retornada pelo software do RSL. Além disso, foi calculada a incerteza de medição relacionada ao cálculo da tensão mecânica na amostra. Os ensaios de verificação do desempenho do RSL foram realizados em amostras de aço AISI 4140 beneficiado com dureza de 40HRC, onde foi avaliada a relação entre o nível de potencial catódico aplicado e a SFH do material das amostras. Os resultados obtidos na validação do equipamento mostraram erros inferiores a 1%. Os resultados mostraram um aumento da SFH com o aumento da dureza indicando que há uma elevada sensibilidade da SFH em relação à dureza da amostra. Os ensaios com variação do potencial catódico mostraram uma relação direta entre esse parâmetro e a SFH da amostra, havendo uma saturação na SFH a partir de -1,1 VAg/AgCl. / Hydrogen embrittlement of metallic materials has been a frequent problem in different industry sectors. Because it is the smallest existing atom, hydrogen diffuses into the microstructure of metallic materials, resulting in internal mechanical stresses that may eventually lead to a catastrophic failure. The most common methods available to analyze this phenomenon are time consuming and expensive. For this reason, it is desired to develop a test method that does not have such disadvantages. In this work it is presented the development of an equipment to rapidly evaluate the susceptibility to hydrogen embrittlement (SHE) of the metallic materials using the rising step load (RSL) bend testing in assisted environment. This equipment has a great advantage over the other evaluation methods of SHE, which is the shortest test time to have representative results. The validation of the infrastructure was performed by testing bars without notches to, whose measured mechanical stress was compared with that returned by the RSL software. In addition, the measurement uncertainty related to the calculation of the mechanical stress in the sample was calculated. The tests to verify the performance of the RSL equipment were carried out on samples of steel AISI 4140 heat treated to a hardness of 40HRC. The effect of the cathodic potential applied to notched bars of AISI 4140 on the SHE was evaluated. The results obtained in the validation phase of the equipment showed errors lower than 1%. The results showed also an increase in SHE with increasing material hardness indicating that there is a high sensitivity to the SHE with respect to the hardness of the sample. The tests carried out using cathodic potential variation showed a direct relationship between this parameter and the SHE of the sample, with saturation of the SHE at -1.1 VAg/AgCl. / Dissertação (Mestrado)

No description available.