The durability of concrete structures is affected by a number of factors such as environmental exposure, electrochemical reactions, mechanical loading, impact damage and others. Of all of these, corrosion of the reinforcement is probably the main cause for the deterioration of steel reinforced concrete (RC) structures. Corrosion management is becoming increasingly necessary as a result of the growing number of ageing infrastructure assets (e.g. bridges, tunnels etc.) and the increased requirement for unplanned maintenance in order to keep these structures operational throughout their design life (and commonly, beyond). The main RC repair, refurbishment and rehabilitation approaches generally employed can be broadly categorised under a) conventional, b) surface treatments, c) electrochemical treatments and d) design solutions. The overarching aim of this research was to identify the key corrosion management techniques and undertake empirical investigations focused on full-scale RC structures to investigate their long-term performance. To achieve this, individual research packages were identified from the above broad five approaches for repair, replacement and rehabilitation. These were 1) Patch repairs and incipient anodes, 2) Impressed Current Cathodic Protection, 3) Galvanic Cathodic Protection and 4) Hydrophobic treatments. The selection of the above research packages was based on past and present use by the construction industry to repair, refurbish and rehabilitate RC structures. Their contributions may be broadly categorised as i) Investigations on how specific treatments and materials perform, ii) Investigations on the effectiveness of existing methods of measurements and developing alternatives, iii) Changes to the existing theory of corrosion initiation and arrest and iv) Changes to management framework strategies. The key findings from each research package can be summarised as follows: Macrocell activity appears to be a consequence rather than a cause of incipient anode formation in repaired concrete structures, as has previously been presented; ICCP has persistent protective effects even after interruption of the protective current; Discrete galvanic anodes installed in the parent concrete surrounding the patch repair are a feasible alternative to galvanic anodes embedded within the patch repairs of RC structures; Silanes may have a residual hydrophobic effect even after 20 years of service.

Graduation date: 1999

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 240-248). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 240-248). Also available on the Internet.

As part of the water resources policy of the state of CearÃ, in Northeast Brazil, COGERH, as an operational instrument, has among its tasks the distribution of bulk water for various uses. Among the water systems that COGERH operates are the pumping stations, which are responsible for supplying water for cities, industries, irrigation, etc. It is vital that these structures operate satisfactorily and efficiently. Among the many devices that make up the pumping stations are the semisubmersible floating metal chambers that are located on the water surface of the reservoirs, providing support to the pumps and motors such that they can be set and operated reliably and efficiently. However, these structures are made from steel and therefore are subject to severe corrosion processes, making it necessary for the painting of the submerged areas to ensure the necessary protection to avoid oxidation of them. As painting alone is not a process that ensures 100% efficiency in terms of coating and has a relatively short lifespan, complementary processes are necessary to ensure safe protection against corrosion. Among these processes is the Cathodic Protection, which ensures that, while a difference in electrochemical potential is being generated between the structure to be protected and a sacrificial anode, the structure will not undergo corrosion processes. For this study, it has been designed and installed an Impressed Current Cathodic Protection System with a potential ON of protection of -2.67 Volts (DC) for the Pumping Station known as "EB GaviÃoâ chosen due to its strategic importance within the state infrastructure of water resources, responsible for supplying water for major cities and industries. Keywords : / Dentro da polÃtica dos recursos hÃdricos do estado do CearÃ, no Nordeste do Brasil, a COGERH, como instrumento operacional, tem entre suas atribuiÃÃes a distribuiÃÃo de Ãgua bruta para usos diversos. Dentre os sistemas que a COGERH operacionaliza estÃo as estaÃÃes de bombeamento, as quais sÃo responsÃveis por abastecer cidades, indÃstrias, irrigantes, etc. à fundamental que tais estruturas operem de forma satisfatÃria e eficiente. Dentre os muitos equipamentos que compÃem as estaÃÃes de bombeamento estÃo Ãs cÃmaras metÃlicas flutuantes emisubmersÃveis que se localizam na superfÃcie de Ãgua dos reservatÃrios, dando sustentaÃÃo para que as bombas e motores possam ser fixados e operados de forma confiÃvel e eficiente. No entanto estas estruturas, por serem de aÃo, estÃo sujeitas a processos de corrosÃo severos, fazendo-se necessÃrio que a pintura das Ãreas submersas assegurem a proteÃÃo necessÃria para que nÃo haja oxidaÃÃo das mesmas. Como a pintura nÃo à um processo que garante uma eficiÃncia de 100% e termos de revestimento e tem uma vida Ãtil relativamente curta, fazem-se necessÃrios processos complementares para uma segura proteÃÃo anti-corrosÃo. Dentre esses processos està a ProteÃÃo CatÃdica que assegura que enquanto estiver sendo gerada uma âdiferenÃa de potencial eletroquÃmicoâ entre a estrutura a ser protegida e um anodo de sacrifÃcio a estrutura nÃo sofrerà severos processos de corrosÃo. Neste estudo foi dimensionado e instalado um Sistema de ProteÃÃo CatÃdica por Corrente Impressa assegurando um potencial ON de proteÃÃo de -2,67 Vcc para a estaÃÃo de bombeamento denominada âEB GaviÃoâ pela importÃncia estratÃgica que ocupa dentro da infraestrutura estadual de recursos hÃdricos, fazendo parte de sistema responsÃvel pelo abastecimento de importantes cidades e indÃstrias.

Marine structures must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum satisfies these conditions, and would be a good choice for a sacrificial anode to protect steel structures if it did not passivate. However, various elements can be added to aluminum to prevent this passivation. Currently, Al-Ga alloys are used commercially as sacrificial anodes but their performance is not consistent. In this research, Thermo-Calc software was used to simulate various aspects of the Al-Ga system in an attempt to understand and potentially correct this reliability issue. Simulations showed that gallium segregates to the grain boundaries during solidification and then diffuses back into the grains during cooling to room temperature. Simulations also suggest that faster cooling rates and larger grains cause the potential segregation of gallium at the grain boundaries to remain after cooling. A set of aluminum plus 0.1% weight percent gallium alloy plates were produced with varying cooling rates, along with a control set (cooled slowly in a sand mold). Some samples were later homogenized via annealing. Samples were subjected to a 168 hour long galvanostatic test to assess voltage response. The corrosion performance of samples was found to have both consistent and optimal voltage range when subjected to quick cooling rates followed by annealing. Testing samples at near freezing temperature seems to completely remove optimal corrosion behavior, suggesting that there are multiple causes for the voltage behavior. / Master of Science / Ships must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum has properties which could allow a plate of it to rust instead of a ship it is attached to, thus protecting the ships from rusting. However, because aluminum usually does not rust, gallium can be added to aluminum to allow it to rust. Currently, aluminum-gallium alloys are used commercially to protect ships, but their performance is not consistent. In this research, various aspects of the aluminum-gallium system were simulated in an attempt to understand and potentially correct this reliability issue. Simulations showed that the gallium concentration may not be uniform in the alloy, and various conditions can cause the gallium concentration to be inconsistent. A set of aluminum-gallium alloy plates were cast in molds from liquid aluminum. Some of the plates were cooled quickly, and some cooled slowly. Some samples were later heated in an oven at high temperatures in an attempt to even out the gallium concentration. Samples were subjected to tests to observe corrosion behavior. The corrosion performance of samples was found to be best when subjected to quick cooling rates followed by the oven heating. Testing the samples in cold temperatures seemed to remove the desired corrosion behavior, suggesting that there are multiple reasons for the inconsistent corrosion behavior of aluminum gallium.

An interdisciplinary study concerning the durability of adhesively elastomer/metal bonded joints in marine environments is reported. The generation of OH⁻ ions at the bondline due to an imposed cathodic current from an external source is suspected to be the predominant cause of failure. A surface analysis study was performed early in this research for the purpose of identifying the cause(s) of failure. Characterization of the rubber and the metal failure surfaces with XPS (X-ray Photoelectron Spectroscopy) showed similar composition on both sides and to that of the bulk degraded primer component of the adhesive. Saponification of the adhesive and the leaching of chlorine (forming HCI that attacks the oxide) are identified as two possible failure mechanisms. The locus of failure is believed to be very close to the . adhesive/oxide interface. The exposure of bulk adhesive free-standing films to different environments showed that the hydroxyl is detrimental in the environmental durability of these specimens judging by the percentage of net mass uptake. An alternate interfacial failure mechanism is also presented where the neutralization of the adhesion-promoting attachment sites (A.S.) at the interface leads to de-adhesion and whereby OH⁻ ions chemically break-up the -COOH-Fe bond forming a non-operative activated complex at the degraded crack tip. Debond, or loss of adhesion, can exist in two modes. Weakening denotes debond growth which takes place undetected to the naked eye, and is governed by a diffusion-control degradation process that gives a straight line when plotted against the square root of time. Delamination, on the other hand, is a "post weakening" process., Debond rates in this mode are influenced by the applied total strain energy release rate, G_T, and by the environment and can be described by an exponential function in G_T. The effect of shear stress on debond acceleration was determined to be minimal. While compressive stresses seem to be beneficial in slowing the ingression of the bulk hydroxyl into the bondline, no noticeable improvement was detected when an imposed current was used. The use of zinc phosphate-coated steel substrates is shown to improve bond durability significantly at low voltages. Similar trends are observed when silane (γ-aminopropyltrimethoxy) modified primer were used in bonding. Two approaches are used in order to model debonding: empirical and analytical. Statistical Analysis System (SAS) is used to fit the empirical model which draws heavily on the functional dependencies of debond rates on the accelerating parameters, i.e., temperature, stress, and applied voltage. An Arrhenius relationship is shown to model the effect of temperature very well. Also, voltage effect is correlated with the corresponding current densities which, in turn, were found to obey an exponential relationship with debond rates. SAS fits of the experimental data are shown to model the process accurately and could be utilized for life predictions. Integration of delamination rates in real time is a feasible method to predict durability as well. A generalized analytical model for debonding is also developed, and it draws on the similarities between this application and corrosion fatigue of metals. The model is based on the conservation of mass of the involved species and is composed of a system of partial equations and their associated boundary conditions. Furthermore, temperature and voltage-dependent diffusion coefficients and reaction rate constants were used. The resulting boundary value problem amounts to a diffusion-chemical reaction mechanism into which a mechano-chemical failure mechanism is incorporated. A simplified version of the full scale analytical model is solved numerically and some interesting conclusions concerning the failure criterion are drawn. The model also simulates the weakening and delamination behavior and allows for temperature and voltage treatment as well. Delay times are also predicted as a function of the applied voltage and temperature. A particularly important conclusion is that the "marching boundary" phenomena seems to account for most of the accelerating influence of applied G. / Ph. D.

The rise of Zn-coatings on direct press hardened steels for body-in-white passenger safety applications over the widely used Al-Si coatings is due to its lower cost, compatibility with Zn-based paint systems, and offers sacrificial cathodic protection in addition to barrier protection. Manufacturing the complexly-shaped high strength automotive parts using the direct hot press forming method (DHPF) transforms the Zn-based coating into a mixture of Γ-Fe3Zn10 and α-Fe(Zn). Previous literature has determined that a minimum of 15 vol% Γ-Fe3Zn10 is required within the coating to provide robust cathodic protection of the steel substrate. This assumed the mixed potential theory is valid for modeling the electrochemical properties of the mixed phase coating; however, the interwoven coating phase morphology results in varying volume fractions of Γ-Fe3Zn10 and α-Fe(Zn). Potentiodynamic polarization scans of GI70 coated 22MnB5 steel annealed at 890°C for various annealing times revealed that Γ-Fe3Zn10 + α-Fe(Zn) coatings with at least 11 vol% Γ-Fe3Zn10 exhibit electrochemical properties insignificantly different from those comprising pure Γ-Fe3Zn10, and behaves similarly to pure α-Fe(Zn) for coatings with less than 11 vol% indicating that the Γ-Fe3Zn10 + α-Fe(Zn) coatings behave as a homogeneous single phase, thus validating the use of the mixed potential theory. Scanning vibrating electrode technique analysis of various galvanic couples determined that Γ-Fe3Zn10 provides strong cathodic protection for the 22MnB5 steel and moderate protection for α-Fe(Zn), while the 22MnB5 steel is only weakly protected by α-Fe(Zn). Separation of the 22MnB5 steel and Γ-Fe3Zn10 by an intermediary α-Fe(Zn) layer reduces the cathodic protection of the 22MnB5 steel since the α-Fe(Zn) layer acts as an electron receptor and limits the macroscale throwing power of Γ-Fe3Zn10. / Thesis / Master of Applied Science (MASc) / Zn-coatings on direct press hardened steels are designed to electrochemically protect the steel substrate from corrosion. Manufacturing automotive parts using the direct hot press forming method transforms the Zn-based coating into a two-phase mixture of Γ-Fe3Zn10 and α-Fe(Zn). The previously determined minimum 15 vol% Γ-Fe3Zn10 required for the coating to provide the steel substrate robust protection assumed that mixed potential theory was a valid model to predict the electrochemical properties of the two phase coating, despite its complex microstructure. It was found that the use of mixed potential theory was valid as it was determined that the Γ-Fe3Zn10 + α-Fe(Zn) coatings behave as a single phase, with robust cathodic protection of direct hot pressed coatings requiring a minimum of 11 vol% Γ-Fe3Zn10. It was further determined that Γ-Fe3Zn10 cathodically protects both the steel and α-Fe(Zn), while α-Fe(Zn) only weakly cathodically protects the steel.

Flexible plastic liners are sometimes installed into new and existing oil and gas pipelines to prevent corrosion of the pipe wall. A practical difficulty of this method is that the plastic liners are permeable to gases, which can collect and form an annular space between the liner and the pipe. If the operating pressure in the pipe decreases then the collected gas can cause the liner to collapse and block the pipe. One method for overcoming this problem is to insert vents at intervals along the liner to allow the gas to escape into the pipe during depressurisation. However, there is concern that this arrangement might lead to excessive corrosion beneath the vent where the pipe wall is exposed. The rate of corrosion is expected to be controlled by the vent size but this principle needs to be confirmed by experiment. The work described in this thesis is aimed at investigating this corrosion by experiment for a range of conditions typical of oil and gas production. A novel crevice corrosion cell was designed, consisting of an X100 carbon steel plate and a sheet of transparent Perspex, separated by a thin gasket. A small hole in the Perspex simulated a liner vent and allowed carbon dioxide to reach the steel surface. Tests were carried out in 3.5% NaCl solutions saturated with carbon dioxide at 1 bar partial pressure. Corrosion rates along the length of the annular space were measured using the Linear Polarisation Resistance (LPR) technique on pairs of insulated X100 electrodes set into the plate. The corrosion rates within the annular space have been shown to be small compared to those in the bulk solution and to diminish rapidly with distance from the vent. Mathematical modelling, based on the transport of carbon dioxide, is described to explain these findings and support the experimental work. The effectiveness of the LinerVentTM, installed over the vent, in a turbulence pipeline was demonstrated. The benefit of applying cathodic protection within the annular space was also demonstrated. The results are discussed in terms of the fundamental corrosion principles and their practical implications

Alumínio Pulverizado Termicamente (TSA) é amplamente utilizado em instalações offshore como revestimento de ânodo de sacrifício em tubulações de aço carbono. O transporte e a instalação desses componentes podem levar a pequenos danos no revestimento, o que pode expor a superfície do aço à água do mar. Sabe-se que o depósito calcário é formado na superfície do aço polarizado catodicamente. Assim, esta pesquisa avaliou o TSA aplicado por sistema de pulverização de arco duplo (TWAS) no aço ao carbono S355J2 + N quando ocorrem danos (holidays) para estudar a formação de depósitos calcários no aço e adquirir dados sobre o desempenho do TSA sob altas temperaturas. A aplicação de diferentes condições também foi considerada: presença de selantes; liga do revestimento (99,5% de Al e Al-5% de Mg) e condições enterradas/não enterradas. Dois tipos de experimentos foram realizados: i) testes em potencial livre sob temperaturas constantes (30, 60 e 90°C) e diferentes tamanhos de holidays (expondo 5, 10 e 20% da superfície do aço) e ii) testes sob gradient térmico onde óleo a ~125°C foi adicionado em uma torre polimérica e água externa a ~10°C ficou em contato com a superfície das amostras (tanto potencial livre como polarização de -950 mVAg/AgCl foram aplicados). Análises incluíram inspeção visual, microscópio eletrônico de varredura e difração de Raio-X. A partir dos testes em temperaturas constante, o TSA atingiu um bom potencial de proteção (-800 a -900 mVAg/AgCl) e pouca diferença nos resultados devido à diferença na composição doTSA e no tamanho do holiday foi observada. As taxas de corrosão foram mantidas entre 0,02 e 0,01 mm/ano. No ensaio sob gradiente térmico e potencial livre, a perda de revestimento e as taxas de corrosão foram de 0,4 a 0,002 mm/ano. Além disso, o potencial alcançado foi de uma faixa menor do que a obtida anteriormente (-745 a -835 mVAg/AgCl). No entanto, quando o TSA foi combinado com proteção catódica externa e gradiente térmico, a espessura do TSA foi satisfatório e as taxas de corrosão obtidas foram inferiores a 0,076 mm/ano. O depósito calcário formado no holiday protegeu o aço contra a corrosão e seu mecanismo de crescimento baseado nesta pesquisa foi construído. / Thermally Sprayed Aluminium (TSA) is widely used in offshore facilities as sacrificial anode coating for carbon-steel risers and pipelines. Transportation and installation of those components can lead to small damages in the coating, which can expose the steel surface to the seawater. It is known that calcareous deposit is formed on the cathodically polarised steel surface. Thus, this research evaluated the TSA applied by twin wire arc spray system (TWAS) on S355J2+N carbon-steel when damage (holidays) is present in order to study the calcareous deposit formation on steel and acquire data regarding the TSA performance at high temperatures. Application of different conditions was also considered: presence of sealing; coating alloy (99.5%Al and Al-5%Mg) and buried/unburied conditions. Generally, two types of experiment were conducted – i) tests at free potential at steady temperatures (30, 60 and 90°C) and different holiday sizes (exposing 5, 10 and 20% of the steel surface) and ii) tests under thermal gradient where oil at ~125°C was added in polymeric tower and external water at ~10°C was in contact with the samples surface (both free potential and polarisation of -950 mVAg/AgCl were applied). Methodology of analyses included visual inspection, scanning electron microscope and X-ray Diffraction. From the tests at steady temperatures, the TSA reached a very good protective potential (-800 to -900 mVAg/AgCl) and little difference in results due to difference in TSA composition and holiday size was observed. Corrosion rates were kept between 0.02 and 0.01 mm/year. From the thermal gradient test under free potential, the coating loss and corrosion rates were 0.4 to 0.002 mm/year. Also, the potential achieved was in a lower range than previously obtained (-745 to -835 mVAg/AgCl). However, when TSA was combined with external cathodic protection and thermal gradient, the thickness of the TSA was satisfactory and corrosion rates obtained were below 0.076 mm/year. The calcareous deposit formed within the holiday protected the steel substrate against corrosion and its growth mechanism based in this research was built.