For concrete, a sustainable design requires considering both mechanical properties and durability. One of the major deterioration modes of reinforced concrete structures is the entry of chloride ions and corrosion of embedded metals, which is mainly controlled by diffusion as the mass transport mechanism. Therefore, it is pivotal to quantify the chloride diffusion coefficient of concrete, which controls the rate of chloride ingress. Several testing methods exist for quantifying diffusivity of concrete. However, the current test methods are time consuming and demanding. The primary goal of this study is to develop models for quantifying the chloride diffusion coefficient of concrete. As such, initially, the most recent and prevailing analytical models proposed in the scientific literature were critically reviewed and the parameters controlling the chloride diffusion coefficient of concrete were identified. Then, the cement degree of hydration of concrete – as a key parameter which controls the properties of concrete – its measurement methods, and the uncertainties associated with different quantification methods were scrutinized. Finally, three models were developed to quantify the chloride diffusivity of concrete. The first model quantifies the chloride diffusivity of concrete in terms of its electrical resistivity based on the modified Nernst-Einstein equation. The model accounts for the ionic concentration of the pore solution through the alkalis released due to hydration of cementing materials and the alkali uptake of hydration products, the pore solution conductivity, and the interaction between the ions in the pore solution. The second model, which provides a phenomenological relationship for chloride diffusivity of concrete in terms of its compressive strength, accounts for the tortuosity factor of the mixture, aggregate volume fraction, porosity, compressive strength, and cementing materials content and composition. The third model is developed based on the mixture constituents and the cement degree of hydration of concrete. The model accounts for tortuosity factor through the volume fraction of aggregate particles, the interfacial transition zone thickness and diffusivity, cementing materials type and chemical composition, bulk cement paste transport properties through water to cementing materials ratio, cement degree of hydration, supplementary cementing materials type and replacement levels. In order to assess the accuracy and precision of the proposed models, an experimental program was developed and conducted. The following variables were considered for the experimental program: the volume fraction of coarse aggregate, water to cementing materials ratio, total cementing materials content, and supplementary cementing materials type and replacement levels. The experimental results along with the reported data in the scientific literature were used to validate the proposed models. The results revealed the capability of the models to capture the documented observations, as well as the high accuracy and precision of the proposed models for quantifying the chloride diffusivity of concrete in a wide range of concrete mixtures composition and age. The developed models provide designers, practicing engineers and standard/code developers with accurate, precise and consistent models for quantifying the chloride diffusion coefficient of concrete as a direct measure of its durability. / Thesis / Doctor of Philosophy (PhD)

This dissertation discusses topics related to the performance and long-term durability of glass-reinforced composites. The first portion of this dissertation describes work to assess the effect that post-curing has on widely used E-glass/vinyl-ester composites (E-glass/Derakane 510-A and E-glass/Derakane 8084). It is shown that post-curing can have significant positive effects on the initial material properties of glass-reinforced vinyl ester composites. Furthermore, the post-cure of 82ºC for four hours stabilizes the matrix, and as such reduces matrix-related material property evolution. By stopping or nearly stopping material property evolution due to matrix curing over time, the post-cure regime isolates and allows the study of other time-dependent effects, such as fatigue or hygrothermal degradation, and aids designers by establishing an unchanging base set of initial (undamaged) material design properties. The second portion of this dissertation discusses the effects that mean stress and R-ratio have on the fatigue performance of the same material. Qualitative and quantitative differences are seen in the performance as a function of the loading ratio. A residual strength based life prediction model developed at Virginia Tech is applied to the fatigue data, characterizing the material under constant-amplitude loading. Three curve-fitting parameters are then used along with the model to predict variable-amplitude fatigue lives, with remarkably good results. The final portion of the dissertation concerns the effect of hygrothermal and accelerated aging on glass-reinforced composites. A meta-study is performed on data from the literature, and a glass-degradation-based life-prediction model is applied to the data. It is seen that a static fatigue-based activation energy approach to residual strength can predict activation energies associated with glass-reinforced composite strength degradation in the case of glass-reinforced concrete quite well, predicting values of 80-100 kJ/mol, which are similar to those expected for glass dissolution via silica ring opening. The model may also hold some promise for doing the same for glass-reinforced polymer composites. / Ph. D.

The primary cause of corrosion in transportation structures is due to chlorides which are applied to bridge decks as deicing salts. The direct cost of corrosion damage to the country's infrastructure is approximately $8.3 billion per year. One of the most common corrosion abatement methods in the United States is the barrier protection implemented through the application of fusion bonded epoxy coatings. The purpose of this study was to investigate various coating and exposure parameters to determine their effects on the corrosion of reinforcing steel. The parameters investigated were: chloride content at the bar depth, coated bar corroded area, corrosion product color under the coating, epoxy coating adhesion, coating color, coating damage (holidays and holes), coating thickness, TGA, DSC and EDS analysis and SEM coating cracking investigation. This was accomplished by testing new coated bar specimens as well as specimens extracted from 27 bridge decks located in Virginia. This study demonstrated the following: The extracted ECR coating samples presented extensive cracking compared to the new ECR samples in which the coating cracking was limited to only one sample. The DSC results showed that both the extracted samples as well as new samples are not fully cured during the manufacturing process. The coating degree of curing data also showed that the bars are insufficiently and unevenly heated prior to the application of the powder coating. Additionally, the samples investigated presented significant permanent adhesion loss with little or no epoxy coating residue present on the bar surface, while the EDS analysis showed that once adhesion is lost, corrosion will proceed unimpeded under the coating even in the absence of chlorides. The parameters that presented a direct correlation with the observed corrosion activity were the number of holidays and the number of damaged areas per unit length of bar. This indicates that the passivation of the bare steel exposed to the concrete pore solution at the breaches in the epoxy coating is not the same as a bare bar under similar exposure conditions allowing it instead to corrode at lower concrete chloride concentration levels than bare bars. The results also show a distinct loss of quality control in the handling and possibly storage of new coated bars. The new ECR samples had significantly higher damage density than the samples extracted from concrete even though the coating is damaged during the placement of the concrete, while there was no change in the number of holidays and cure condition. Finally, the data presented further evidence that while limited, the non-destructive corrosion assessment methods available for bare steel reinforced structures may also be used on ECR reinforced structures. In particular, the corrosion rate measurements correlated reasonably well with the chloride concentrations at bar level. This indicates that while the chlorides may not influence the corrosion activity under the coating, they do influence the corrosion activity at breaches in the coating. / Ph. D.

Novel coatings have been designed to solve problems associated with biofouling of marine structures, particularly ship hulls. The best candidates to date are multilayered coatings incorporating silicone rubber technology. These materials are efficient because they exhibit excellent release properties. However, they are very soft and tend to be more susceptible to various forms of mechanical damage. Fundamental analysis of the durability of these coatings has been done using standard laboratory tests. Simulative studies are essential to screen candidates as well as to predict the true life of the systems. The goal of this project was to develop a testing protocol for the evaluation of the durability of elastomeric easy release coatings and to implement it on selected candidate coatings. A brushing apparatus was designed and built to simulate the cleaning processes of ship hulls. Wear was measured with profilometry. The proposed methodology is valuable to study the processes of wear of the coatings, to screen various materials and to identify parameters, either functional or material, which would directly affect their durability. Two groups of candidate coatings were tested: the EXS series and the NRL series. The EXS samples showed better wear resistance than the NRL samples and showed no dependence on the rotational speed of the brushes. The NRL samples showed that increasing the sliding speed resulted in a decrease in wear. An increase in the applied load resulted in increased wear for both sample series. The effect of coating thickness was also investigated and discrimination between the proposed coatings could not be established because the tips of the bristles were sharp and irregular. Scratches matching the path of the brush bristles were observed in the wear scars of both sample types under all load and speed conditions. The NRL samples also exhibited ridges perpendicular to the sliding direction similar to the abrasion pattern. / Ph. D.

Carbon/epoxy laminates are receiving greater attention by the infrastructure, marine, and offshore oil industries due to the need for superior performance capabilities. Such applications generally involve subjecting materials to harsh temperature and moisture conditions. The objective of this study was to provide a greater understanding of how temperature and moisture affect the strength and fatigue behavior of carbon/epoxy composites and the issues involved in modeling these effects. Results from thermal analysis and quasi-static testing on neat resin and unidirectional laminates as a function of temperature and moisture are presented which provide insight into how material properties vary with temperature and moisture and form the inputs necessary to evaluate composite strength and damage models. Fatigue life and damage accumulation testing results provide further insight into the effects of temperature and moisture and also provide a means for model validation. Generally, composite strength was found to be compromised by temperature but enhanced with moisture, while fatigue life was reduced by both temperature and moisture. Crack density with fatigue cycles was found to decrease with temperature but increase for immersed fatigue. Testing also revealed discrepancies between the edge replication and radiography methods for determining crack density. The analytical phase of the work considered a composite strength model and a damage evolution model to predict crack density. The composite strength model was found to provide an accurate dry, room temperature prediction which could be extended to an accurate prediction of wet specimen strength, but the results at elevated temperature fell conservative. The validation of the damage model proved inconclusive as it was found that the results are very sensitive to quantities such as thermal residual stresses and first ply failure. Currently, no reliable methods are available in the literature to determine these values accurately. However, the model was able to predict the decrease in crack density at elevated temperatures. The increase in crack density for immersed fatigue was not predicted. Overall, the study revealed that a more basic understanding of "in-situ" ply properties are needed before one can consider the use of predictive models in practical applications, especially in varying environments. / Ph. D.

The increased use of wood composites in building materials results in a need for a better understanding of wood adhesion. The effects of water and temperature exposure on the durability of wood products were assessed using the double-cantilever beam (DCB) method of fracture testing. The relative durability of phenol-formaldehyde (PF) and isocyanate (pMDI) adhesives was compared using a 2-hour boil test and an environmental test. The feasibility of using oriented strandboard (OSB), oriented strand lumber (OSL) and parallel strand lumber (PSL) for the DCB fracture method was assessed. The fracture resistance of PF was reduced significantly by the aging exposures. The fracture resistance of pMDI did not decrease after the 2-hour boil test. The DCB fracture method was shown to be useful with a square-grooved machined specimen using OSB and OSL. / Master of Science

Yes / The paper presents a new healing system that uses pre-tensioned hybrid tendons to close cracks in cementitious structural elements. The tendons comprise an inner core, formed from aramid fibre ropes, and an outer sleeve made from a shape memory PET. During the manufacturing process, the inner core of a tendon is put into tension and the outer sleeve into compression, such that the tendon is in equilibrium. A set of tendons are then cast in a cementitious structural element and heat activated once cracking occurs. This triggers the shrinkage potential of the PET sleeve, which in turn releases the stored strain energy in the inner core. The tensile force thereby released applies a compressive force to the cementitious element, in which the tendons are embedded, that acts to close any cracks that have formed perpendicular to the axis of the tendons. Details of the component materials used to form the tendon are given along with the tendon manufacturing process. A set of experiments are then reported that explore the performance of three different tendon configurations in prismatic mortar beams. The results from these experiments show that the tendons can completely close 0.3 mm cracks in the mortar beams and act as effective reinforcement both before and after activation. A nonlinear hinge-based numerical model is also described, which is shown to be able to reproduce the experimental behaviour with reasonable accuracy. The model is used to help interpret the results of the experiments and, in particular, to explore the effects of slip at the tendon anchorages and the amount of prestress force that remains after activation. It is shown that, with two of the tendon configurations tested, over 75% of the prestress potential of the tendon remains after crack closure. / UK-EPSRC (Grant No. EP/P02081X/1, Resilient Materials 4 Life, RM4L).

Yes / This work presents the design of a smart activation system for the crack-closure technology of the Hybrid Tendons. Previous research has demonstrated the effectiveness of this technology in providing a self-repairing mechanism for concrete elements. The Hybrid Tendons are made combining a pre-stressed Kevlar inner core restrained by a Shape Memory Polymer sleeve. To trigger the crack-closing action, the Shape memory potential of the outer sleeve needs to be activated via heating. The work focuses on the design and testing of an electric activation system for the Hybrid Tendons using a system of heating wires. Kanthal wires are chosen for this application and integrated in the manufacturing process of the Hybrid Tendons: the wires are wrapped around each tendon and connected to a power supply. An experimental campaign is conducted to assess the system's capability to activate the Hybrid Tendons and deliver the crack-closing action in concrete beams under constant load. Additionally a numerical model is also developed to offer a sound interpretation of the experimental results. The system is ultimately proven successful in activating the Hybrid Tendons embedded in the concrete, effectively delivering the crack-closing action and boosting the flexural response of the structural element. / UKRI-EPSRC (Grant No. EP/P02081X/1 , Resilient Materials 4 Life, RM4L), Leverhulme Trust ECF-2022-235.

Orientador: Vanessa Gomes da Silva, Maristela Gomes da Silva / Acompanha 1 CD-ROM de Apendices e Anexo / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-15T14:55:12Z (GMT). No. of bitstreams: 1 Ramadan_JussaraTanesi_D.pdf: 9121770 bytes, checksum: 922d5751838ca1dc378ab9d1297f680e (MD5) Previous issue date: 2010 / Resumo: A produção anual de aço em 2008 foi de cerca de 31 milhões de toneladas O processo siderúrgico gera em média 500 kg de resíduos e co-produtos por tonelada de aço produzido. Desse total, 70% correspondem à geração das escórias. Investigar a possibilidade de moagem da escória de alto-forno para atender às usinas de concreto e indústrias afins é de vital importância como estratégia de sustentabilidade sócioambiental para a cadeia produtiva do aço e do concreto. No entanto, as atuais normas e especificações brasileiras de concreto se apresentam como um obstáculo para isso. Atualmente, a maioria das especificações de concreto é predominantemente prescritiva com alguns aspectos de desempenho. As especificações prescritivas impedem o uso de soluções mais inovadoras que potencialmente podem resultar em produtos com desempenho comparável ou até melhor do que aqueles que são produzidos de acordo com as especificações prescritivas. A solução para o avanço tecnológico é o uso de especificações por desempenho. As especificações por desempenho tratam do que se requer do produto e não prescreve como esse produto deve ser produzido. Em outras palavras, ao invés de partirem dos materiais que compõem o concreto, partem do desempenho desejado, deixando a seleção dos materiais, a dosagem e os métodos construtivos a cargo daqueles que contratualmente devem atender às especificações. Há uma necessidade crescente da inclusão de requisitos de desempenho nas especificações e normas, referentes à durabilidade do concreto, especialmente no que concerne a capacidade de proteção do concreto contra a corrosão da armadura. Isso requer que o desempenho da estrutura, ao longo da sua vida útil, possa ser estimado. Para isso, são necessários modelos de previsão de vida útil que correlacionem os requisitos e subrequisitos de durabilidade, medidos em laboratório por meio de ensaios acelerados, e o desempenho em serviço, obtido por meio de dados nas condições reais. Este trabalho apresenta um estudo laboratorial em concretos com escória de alto-forno, avalia suas principais propriedades, principalmente as relativas à deterioração referente à armadura. Foram avaliados: a retração, a absorção capilar, a resistência à compressão axial, o módulo de deformação, a carbonatação tanto natural quanto acelerada, a carga passante, a resistividade elétrica e o efeito sinérgico da carbonatação e da penetração de cloretos sobre a corrosão da armadura. Este efeito sinérgico foi avaliado por meio de ensaios cíclicos e a medida da profundidade de penetração de cloretos, da profundidade de carbonatação, da resistividade elétrica e do potencial de circuito aberto. Com os resultados obtidos neste estudo, verificou-se que a utilização de elevados teores de escória de alto forno, de maneira geral, ou não teve nenhuma influência ou exerceu uma influência positiva sobre as propriedades estudadas, com exceção da retração e da carbonatação acelerada. Os ensaios cíclicos apresentaram uma maneira de avaliar-se o efeito sinérgico da carbonatação e dos cloretos. Quando todos os resultados de ensaios acelerados cíclicos são comparados observa-se que, de maneira geral, as misturas com CP III-32-RS apresentaram o melhor desempenho no que concerne à corrosão das armaduras. Já os ensaios naturais não foram conclusivos. Além disso, este trabalho avalia a vida útil potencial desses concretos por meio da aplicação de modelos de previsão de vida útil. Independentemente do modelo utilizado para a previsão da despassivação por cloretos, a vida útil prevista aumentou com o aumento do teor de escória de alto-forno. De maneira geral, vida útil das misturas cresceu na ordem CPII-E-32, CP III-32-RS e CP III-32-RS + escória e com o aumento da classe de resistência. No entanto, observou-se que as recomendações da NBR 6118/2003 nem sempre garantem que a durabilidade da estrutura seja necessariamente atingida e não diferenciam misturas cujos desempenhos mostraram-se bem diferentes. As recomendações da NBR 6118/2003 mostraram-se inadequadas para a que uma vida útil mínima aceitável seja atingida. A partir desta avaliação de desempenho, apresentam-se sugestões para a modificação das especificações e normas brasileiras a fim de que sigam a tendência mundial e passem de prescrição ao desempenho. Diretrizes para a criação de especificações por desempenho de concretos com escória de alto-forno, incluindo sugestões para os requisitos e subrequisitos de desempenho, bem como os aspectos estratégicos, táticos e operacionais de sua implementação no Brasil também são apresentados / Abstract: In 2008 alone, the annual steel production in Brazil was around 31 million tons. The steel production process generates an average of 500 kg of residues and co-products per ton of steel. From this total, 70% corresponds to the slags. Although investigating the increase of blast furnace slag use is of extreme importance for the concrete and steel industries' socio-environmental sustainable strategy, the current Brazilian standards and specifications represent a barrier. Currently, most concrete specifications are predominantly prescriptive with some performance requirements. Prescriptive specifications prevent the use of innovative solutions that can potentially result in products with comparable or even better performance than those produced according to prescriptive specifications. The solution for the technology progress is the use of performance specifications. Performance specifications stipulate what is required from the product and do not prescribe how the product should be produced. In other words, they focus on the desired performance rather than on the concrete ingredients, materials selection, proportioning or construction methods. These are the responsibility of those individuals who contractually have to comply with the specifications. There is an increasing need to include performance requirements related to durability in specifications and standards, especially those related to reinforcement deterioration. It requires the performance of the structure to be estimated during its service life. It also requires service life prediction models which can correlate the durability requirements, measured through laboratory testing, and the performance in service, obtained from real exposure condition data. The present thesis presents a laboratory study on concretes containing blast furnace-slag, evaluates their main properties, especially those related to reinforcement deterioration. The following properties were evaluated: shrinkage, capillary absorption, compressive strength, modulus of elasticity, natural and accelerated carbonation, charge passed, electrical resistivity and the synergic effect of carbonation and chloride penetration on the reinforcement corrosion. This synergic effect was evaluated through cyclic testing and the measurement of chloride penetration, carbonation depth, electrical resistivity and open circuit potential. The results of this study showed that the use of high blast furnace slag contents generally either did not have an impact or had a beneficial impact on the properties studied, with exception of shrinkage and accelerated carbonation. The cyclic testing presented a way to evaluate the synergic effect of carbonation and chlorides. When all the accelerated cyclic test results are compared, it can be observed that in general the mixtures containing CP III-32-RS presented a better performance regarding reinforcement corrosion. On the other hand, the natural tests did not present any conclusive results. In addition, this thesis evaluated the potential service life of these concretes through mathematical models. No matter which model was used to predict corrosion initiation due to chloride ingress, the predicted service life increased with the increase of the blast furnace slag content. Generally, the service life of the mixtures increased in the order CPII-E-32, CP III-32- RS e CP III-32-RS + slag and with the increase of the compressive strength. Nevertheless, it was observed that NBR 6118/2003 recommendations do not always guarantee the structure durability and do not differentiate mixtures that performed considerably differently. NBR 6118/2003 recommendations were identified as inadequate to assure an acceptable service life. Based on the performance evaluation of the mixtures, changes to the Brazilian specifications and standards were suggested in order to follow the international trend and to move from prescription to performance. Guidelines to develop performance specifications for concretes containing blast furnace slag were presented, including suggestions for the performance requirements and sub-requirements. The strategic, tactic and operational aspects for their implementation in Brazil were presented, as well / Doutorado / Arquitetura e Construção / Doutor em Engenharia Civil

Diploma thesis discusses and summarizes the problematic how ovality effects durability of bended tubes. The work presents an approach to the solution, the experiments concerning change of ovality, changes in the thickness of the distorted cross-section. Final results represent connection between ovality and durability.