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This thesis quantifies the flexural behavior (strength, stiffness and failure) of IsoTruss®-reinforced concrete beam-columns for use in deep foundation pile applications. Four-point bending tests were performed in the laboratory on two instrumented carbon/epoxy IsoTruss® reinforced concrete piles (IRC piles) and two instrumented steel reinforced concrete piles (SRC piles). The piles were approximately 14 ft (4.3 m) in length and 14 in (36 cm) in diameter and were loaded to failure while monitoring load, deflection, and strain data. The steel and IsoTruss®® reinforcement cages were designed to have equal flexural stiffness to permit a relative strength comparison. Moment curvature diagrams reveal that the stiffness values were indeed close, verifying the design objective. At failure, the IsoTruss®-reinforced concrete beams held nearly twice the bending moment as the steel-reinforced concrete beams [1,719 kip-in vs. 895 kip-in (194 kN-m vs.101 kN-m)], although the failure modes were quite different. The SRC piles exhibited the traditional ductile failure behavior, as expected, while the IRC piles lacked ductility. The IRC pile deflections remained linear to failure, while the SRC piles yielded significantly. At 35 kips (165 kN), the maximum load on the SRC piles, the ductility of the SRC piles was twice that of the IRC piles (0.0084 and 0.0042, respectively). Toughness measurements reveal that due to the lack of ductility in the IRC piles, the SRC piles absorbed approximately twice as much energy as the IRC piles. Further investigations are required to explain the absence of ductility in the IRC piles, since ductility has been observed in other IsoTruss®-reinforced concrete structures in flexure. Even with this low level of ductility, the IRC piles are substantially stronger than the SRC piles and provide an alternative for use in deep foundation environments. Not only is the IRC pile strong enough for the job, but the IsoTruss® reinforcement is approximately 62% lighter, more rigid, and more corrosion resistant than the steel reinforcement.

Fiber reinforced polymer (FRP) composites have been of interest to the structural engineering society since the earliest days of FRP composites industry. The use of such systems has been implemented in both new construction and for repair and rehabilitation of existing structures. Since the 1980s, researchers have developed a significant body of knowledge to use FRP composites in infrastructure applications; however, most of this established knowledge was concentrated on the use of traditional epoxy (EP) systems (epoxy matrix FRPs and epoxy adhesives). FRP composites with polyurethane (PU) matrices and adhesives have recently attracted the attention of a few researchers due to their potential advantages in constructibility and mechanical properties. The deployment of these systems is currently limited by a lack of knowledge on mechanical and durability performance. The objective of this research is to quantify the mechanical behavior of PU composites utilized in externally-bonded repair of common flexural and flexural-axial reinforced concrete systems. In addition, the mechanical performance, strength, and failure modes are compared directly with an epoxy-based composite by subjecting reinforced concrete specimens utilizing each of the matrix types (EP and PU) to the same protocols. The study presented therefore allows an objective comparison (advantages and disadvantages) between the two composite system used for repair and rehabilitation of concrete infrastructure. An experimental research program was designed with different length scales. Small-scale experiments were utilized to characterize the component level properties of the materials and bond to concrete, which include the flexural behavior as well as the pure shear behavior. The results of these small scale experiments were used to calibrate analytical models of the interface behavior between FRP laminate and concrete, and paved the way for the next level of the research which studied the behavior of each composite system at larger scales. The large scale experiments included flexural retrofitting of reinforced concrete girders and retrofitting of circular columns using FRP laminates. The large-scale experimental specimens were mechanically damaged prior to FRP repair and testing, making the testing more appropriate compared to common practice of repairing undamaged specimens.

The first paper, “Dye Penetrant Induced Microcracking in High-Performance Thermoplastic Polyimide Composites”, studied the possibility of spurious microcracking in three high-performance thermoplastic polyimide composite materials due to zinc iodine dye penetrant. The material systems were IM7/LaRC™-IAX, IM7/LaRC™-IAX2, and IM7/LaRC™-8515. Specimens from each material system were subjected to one of three immersion tests. The first immersion test involved soaking composite specimens previously prepared with different polishing techniques in dye penetrant. In the second test, specimens were immersed in the individual components of the dye penetrant. The final test involved exposure of specimens to one of six solvents followed by exposure to dye penetrant. Results showed that the composite materials have sufficiently high thermal residual stresses to drive microcracking in the presence of dye penetrant without external mechanical loading. There was no evidence that the different polishing techniques had an effect on dye penetrant-induced stress cracking. The dye penetrant components did not produce microcracks in the composites. Some combination of the components must be present to induce microcracking. Observations also revealed that polishing had an effect on the microcracking process of the composites that were initially exposed to solvents then dye penetrant. The second paper, “The Effect of Environmental Stress Cracking on High-Performance Polymeric Composites”, studied solvent stress cracking and solvent-induced strength degradation on four polyimide matrix materials developed at NASA-Langley Research Center. These materials are LaRC™-IAX, LaRC™-IAX2, LaRC™-8515, and LaRC™-PETI-5. Cross-ply specimens were used to characterize solvent stress cracking in composites. Matrix cracking due to solvent exposure was observed in all of the materials. The solvent exposure time of the materials ranged from 1 minute to 96 hours. The results show that residual thermal stresses due to processing in the cross-ply composite specimens are sufficient to drive solvent stress cracking in the matrix. Solvent application lowers the microcracking toughness, G_mc ,values such that the available strain energy, G_m, within the transverse ply groups is sufficient to initiate microcracking. In the absence of a solvent, the same G_m value would not induce microcracking. Transverse flexure tests were performed on unidirectional specimens to determine the effects of the solvents on the material strengths. The presence of certain solvents severely degraded the materials. The manner in which the solvents were applied to the materials determined the degree of material degradation. The results revealed a synergistic effect between stress and solvent. The tests showed that diglyme, MEK, and acetone produced the most severe damage to the materials. The most solvent resistant material was LaRC™-PETI-5. This is followed by LaRC™-8515, LaRC™-IAX2, and LaRC™-IAX respectively. LaRC™- PETI-5 is a thermoset whereas the remaining materials are thermoplastics. / Master of Science

Recently, additive manufacturing (AM), or "3D printing," is expanding into civil infrastructure applications, particularly cementitious materials. To ensure the safety, health, and welfare of the public, quality assurance and quality control (QA/QC) methods via standardized testing procedures are of the upmost importance. However, QA/QC methods for these applications have yet to be established. This thesis aims to implement existing ASTM standards to characterize additive manufactured cementitious composites and to gather better information on how to tackle the challenges that are inherent when printing with cementitious materials. In this work, fresh mix properties and hardened concrete properties were investigated using current ASTM standards as a starting point for applying or adapting them for AM applications. Specifically, this project applied existing ASTM standards for fresh mix mortars to measure setting time, flow, and early compressive strength as qualitative indicators of printability, pumpability, and buildability. The fresh mix properties were investigated for 12 different mortar mixes to demonstrate the effect that moisture content, absorption, and sand type can have on these fresh mix properties. The results for setting time and compressive strength demonstrated that there was less variability in the properties when the moisture condition of the aggregate was measured and accounted. Flow was shown to be strongly influenced by the sand type. Additively manufactured mortars were used to print a box in a layer-by-layer process. To evaluate the effect of layering on the flexural strength, three-point bending tests were implemented using four different loading orientations to explore the anisotropic mechanical properties. The observed anisotropic behavior was corroborated with stereo-digital image correlation data showing the stress-strain and load-deflection relationships. Two orientations (A and B) demonstrated brittle behavior while the other two orientations (C and D) experienced quasi-brittle behavior. In addition, setting a minimum unit weight of 132 pcf enabled an analysis of the effect that defects had on the mechanical performance: specimens greater than 132 pcf demonstrated greater and less variable strengths than the specimens less than 132 pcf. The discussion of how defects impacted performance of the different orientations can be valuable when determining how to effectively model, design, and inspect 3D printed structures in the future. The findings of this thesis confirm that existing ASTM standards for mortars can be modified and applied to AM cementitious composites for QA/QC. It is recommended that mixtures used in 3D printing of cementitious composites should design and accommodate the moisture condition of the aggregate to optimize the predictability of the fresh and early-age properties. For the hardened properties, it is recommended that testing procedures such as flexural testing account for anisotropic behavior. Furthermore, for implementation of 3D printed concrete structures, it is highly recommended that design is a function of loading orientation due to the anisotropic properties of the composite. / Master of Science / Recently, additive manufacturing (AM), or "3D printing," is expanding into civil infrastructure applications, specifically cementitious materials such as mortar and concrete. Understanding and predicting the behavior of the materials when using this new technique is vital for quality assurance and quality control (QA/QC). However, standard test methods have yet to be established for this new construction technique. This thesis aims to use existing testing standards to characterize AM cementitious composites and to gather better information on how to tackle the challenges of printing with these materials. In this work, properties before and after the materials hardened were studied by adapting current testing standards. Specifically, this project applied existing testing standards for fresh mix mortars to measure setting time, flow, and early compressive strength. These properties can serve as indicators of specific printing requirements. The fresh mix properties were studied for 12 different mortar mixes to show the effect of moisture content, absorption, and sand type. The results suggest that there was less variability in the properties when the moisture condition and type of the aggregate was accounted. The fresh mix materials were printed in a layer-by-layer process and then hardened in place. The effects of the layers were explored by performing flexure tests using four orientations with respect to how the load was applied to the layers. The observed difference in behavior for the different orientations was supported by digital image correlation data. In addition, an analysis of the effect defects had on the performance was included. Understanding how defects impacted performance can be valuable for effectively designing 3D printed structures in the future. The results of this thesis confirm that existing testing standards for mortars can be adapted and applied to AM cementitious materials for QA/QC. It is recommended that mixtures used in 3D printing of cementitious materials should account for the moisture condition of the aggregate to improve the predictability of the fresh and early-age properties. For the hardened properties, it is recommended that the design is a function of loading orientation due to the difference in behavior for the different orientations of the material.

Preplaced aggregate concrete (PAC) is produced by grouting high workability cement based grouts among the voids of compacted coarse aggregate mass. Because of its low shrinkage, PAC has been used for many repair jobs like; tunnel lines, dams and bridge piers. Moreover, it has been used for underwater construction. Grout has a major effect on the properties of produced PAC and well defined grout controls the properties of resulted PAC. The effect of types and amount of powder materials, admixtures, sand and water content on the properties of fresh and hardened grout for the production of PAC have been investigated. Tests on hardened grout and PAC properties have also been carried out to investigate the most important effects. A correlation between hardened properties of grout and PAC has also been analyzed. Grout rheology using four different gradation sands at two different cement-sand and at different w/c ratios ratios has been identified experimentally; no added chemical admixtures or mineral additives had first employed, then superplasticizer (SP) was added at 2% and 1%, and finally a combination of 1% SP and pulverized fuel ash (Pfa) at 20% of the cement weight was employed for all mixes. Grout tests have included two point workability tests by the Viskomat NT, flow time funnel test, Colcrete flow meter test, and water bleeding test. After that, eighteen grout mixes with high workability were produced using three different sands at three w/c ratios and two c/s ratios with 1% SP and Pfa at 20% of the cement weight were designed. Eighteen hardened grout and PAC then produced and their compressive strength and sorptivity were tested. Grout rheology can be defined by the rheology of cement paste employed and the internal distance between sand particles. The effect of sand surface texture on grout rheology is important at very low internal distances. Fresh grout yield stress is the most important property which gives the same degree of sensitivity for all grouts regardless the material type and content used in the mix. There are strong relations between compressive strength of grout and PAC, but less correlation between them in sorptivity test because of the effect high quantity of coarse aggregate of PAC. Sorptivity of PAC is low comparing with different kinds of concrete suggesting its advantage for underwater construction.

Dans le contexte général lié aux économies d’énergie, l’amélioration sensible du rendement des turbines à gaz (aéronautiques ou terrestres), nécessitera d’augmenter notablement la température des gaz de combustion. Cela implique l’emploi de matériaux stables au-delà de 1 500°C. Les céramiques eutectiques préparées par solidification dirigée, à partir des systèmes Al2O3 - Ln2O3 (où Ln représente un élément lanthanide ou l’yttrium) sont une solution envisageable. En effet, leur microstructure, constituée d’un réseau interpénétré 3D de deux phases monocristallines, et exempte de pores, de colonies et de joints de grains, confère à ces systèmes eutectiques des propriétés mécaniques d’un bon niveau, et quasi-constantes jusqu’à des températures proches de leur température eutectique (> 1 700°C). Nos travaux ont consisté à élaborer plusieurs systèmes eutectiques binaires et ternaires, par ajout d’une phase ZrO2 renforçante. Les six systèmes présentant les microstructures les plus prometteuses (3 binaires : Al2O3 - Y3Al5O12, Al2O3 - Er3Al5O12, Al2O3 - GdAlO3, et 3 ternaires : Al2O3 - Y3Al5O12 - ZrO2, Al2O3 - Er3Al5O12 - ZrO2, Al2O3 - GdAlO3 - ZrO2) ont été retenus pour étudier certaines de leurs propriétés mécaniques. Plusieurs modes de fissuration, allant dans le sens de l’augmentation de ténacité détectée dans ces systèmes, ont été décelés après des essais de flexion biaxiale. Ces modes de fissuration ont été corrélés aux caractéristiques microstructurales et à la distribution des contraintes résiduelles, déterminées par le calcul et mesurées par une méthode piézo-spectroscopique. Enfin, l’étude du comportement en fluage à haute température a permis de mettre en évidence une évolution des mécanismes de déformation en fonction des conditions de sollicitation. L’étude MET post mortem a également souligné l’influence marquée du caractère interconnecté de la microstructure sur le comportement en fluage. / In the general context of energy savings at a global scale, the improvement of the thermal efficiency of both terrestrial and aeronautical gas turbines will require to increase the turbine inlet gas temperature. The development of new materials, stable up to 1 500°C, is thus necessary. In this context, Directionally Solidified Eutectic Ceramics (DSEC), prepared from Al2O3 and Ln2O3-based systems, could be a potential solution. Their microstructure consists of two single-crystal phases continuously entangled in a threedimensional interpenetrating network without grain boundaries, pores or colonies. The outstanding stability of these microstructures gives rise to a high strength and creep resistance at high temperature. Our research consisted first in obtaining, by directional solidification, several eutectic systems, either binary or ternary (with addition of a toughening third ZrO2 phase). The six most promising DSEC (3 binary systems: Al2O3 - Y3Al5O12, Al2O3 - Er3Al5O12, Al2O3 - GdAlO3, and 3 ternary systems: Al2O3 - Y3Al5O12 - ZrO2, Al2O3 - Er3Al5O12 - ZrO2, Al2O3 - GdAlO3 - ZrO2) have then been selected to study some of their mechanical properties. Several crack propagation patterns have been detected after biaxial flexure testing, and partially explain the toughening which has been proven for DSEC. Attention has been paid to the possibility of crack deflection in the various phases and in the phase boundaries, a phenomenon which may markedly improve the toughness of these eutectic ceramics. These observations have been correlated to internal stress calculations and piezo-spectroscopic measurements. Finally, the study of the creep behavior showed that the deformation mechanisms evolve with the macroscopic solicitation (temperature and stress). microstructure. Moreover, post mortem TEM observations exhibited that creep mechanisms are strongly dependant on the entangled microstructure.

A busca por novos materiais estruturais visa a melhoria da qualidade e desempenho das estruturas, impulsionando o desenvolvimento científico e tecnológico. O concreto auto-adensável surgiu da necessidade de se dispensar o difícil e oneroso trabalho de vibração do concreto, sendo definido como um material capaz de fluir dentro de uma fôrma, passando pelas armaduras e preenchendo a mesma, sem o uso de equipamentos de vibração. Esta pesquisa caracteriza-se como um estudo teórico-experimental da aderência aço-concreto, utilizando concreto do tipo auto-adensável, mediante ensaios monotônicos de flexão em vigas e de arrancamento seguindo o modelo padrão do Rilem-Ceb-Fip (1973). O estudo considerou como parâmetros fundamentais o tipo de concreto (auto-adensável e convencional), a resistência à compressão do concreto e os diâmetros das barras. Ainda, realizou-se um estudo com relação à variabilidade do concreto auto-adensável nos estados fresco e endurecido, constatando que este possui pequena variação. De posse dos resultados, buscou-se verificar a previsão das formulações empregadas na literatura e pelos principais códigos internacionais. De acordo com os resultados, o comportamento dos modelos de viga e de arrancamento para ambos os concretos foi similar, mostrando que o concreto auto-adensável possui características semelhantes ao concreto convencional, com as vantagens da trabalhabilidade no estado fresco. Quanto à análise numérica, os modelos desenvolvidos representaram de forma satisfatória o comportamento dos ensaios, e forneceram uma idéia do comportamento da tensão de aderência na sua interface. Com relação às formulações teóricas, verificou-se que tanto para o concreto convencional quanto para o auto-adensável, ocorre uma superestimativa da resistência de aderência. / The search for new structural materials aims the improvement of the structures performance, pushing the scientific and technological development. Self-compacting concrete (SCC) origin was due to the need to avoid the difficult and expensive process of concrete vibration. It has been defined as a material capable to flow inside a formwork, passing through the reinforcement and filling it completely, without using of any special equipment. This research is characterized as a theoretical and experimental study of steel-concrete bond, using SCC, through pull-out tests and beam tests standardized by Rilem-Ceb-Fip model. The study considered as main parameters the concrete type (ordinary concrete and SCC), its compressive strength and the steel bars diameters. Yet, a study of the variability of the properties of SCC, both in fresh and hardened state was also performed, showing that SCC is a very reliable material. The obtained results were compared with the ones established by the related bibliography and by the main international codes. According to the results, the behavior of the beams and pull-out tests were very similar for both concretes (SCC and OC), with the well know advantages for the SCC in fresh state. About the numerical approach, the developed models represented satisfactory the test behavior (beam and pull-out) and gave an idea of the bond stress behavior on the steel-concrete interface. About the theoretical formulations, it was verified the they usually overestimate the bond strength, for both types of concrete.

Embora sejam reconhecidas diversas vantagens na adição de fibras curtas de aço ao concreto (CRFA), em especial o ganho de tenacidade, pouco se sabe a respeito da fluência desses materiais compostos. Este trabalho teve como objetivo principal investigar o potencial e as dificuldades inerentes de um método de avaliação experimental da fluência pelo ensaio de vigas, como possível alternativa aos ensaios de compressão axial já consagrados. Ao mesmo tempo, considerando a nova tendência de exploração de compósitos híbridos - formados por fibras de diferentes características, de modo a obter respostas adequadas aos processos de micro e macrofissuração - tomou-se como objeto de estudo experimental um conjunto de modelos e corpos-de-prova de CRFA comum e de CRFA híbrido, este formado pela combinação de fibras de aço de diferentes comprimentos, umas mais longas e outras mais curtas. Para caracterização dos materiais, foram efetuados ensaios para determinação das principais propriedades mecânicas de interesse em distintas idades. As proporções da mistura adotada neste programa experimental foram baseadas em dados de estudos anteriores, que suscitaram investigações mais detalhadas. Entretanto, neste particular programa de ensaios, a adição das fibras, principalmente as mais curtas, acarretou maior teor de ar incorporado ao compósito, o que penalizou o seu desempenho em alguns aspectos. Os resultados desses ensaios demonstraram pouca influência das fibras sobre as propriedades de resistência à compressão, módulo de elasticidade e resistência à tração por compressão diametral. Quanto à fluência, o desempenho do CRFA e do compósito híbrido foi inferior ao da matriz. Por outro lado, notou-se maior restrição à retração do concreto com a adição de fibras. Na análise dos resultados experimentais, o estudo das flechas diferidas foi efetuado pelas correspondentes deformações, para interpretação do fenômeno por meio das curvas de fluência específica. O ajuste de resultados experimentais para curvas de fluência específica demonstrou que a fluência em vigas, apesar de apresentar - comparativamente aos modelos teóricos fundamentados em ensaios de compressão - maior taxa inicial, maiores coeficientes de fluência e estabilização aparentemente mais rápida, pode ser representada por modelos teóricos semelhantes aos usuais. As curvas de tendência determinadas para a matriz foram comparadas com aquelas derivadas de expressões dadas por normas técnicas (NBR 6118:2003 e ACI209:1982), assim como com as obtidas em simulações numéricas efetuadas como software DIANA®. A fluência também foi avaliada experimentalmente em vigas entalhadas, submetidas apenas à ação do peso-próprio, sendo estes ensaios também simulados por meio de modelagem numérica e aplicação de conceitos da mecânica da fratura. Os resultados analisados permitem dizer que há possibilidade de avaliar a fluência pela metodologia estudada, o que oferece um método alternativo para avaliação experimental da fluência. Nesta pesquisa, avaliou-se também a alteração de rigidez das vigas ensaiadas em decorrência dos efeitos do tempo, por meio de ensaios dinâmicos de vibração livre, segundo a ASTM C-215:1991a. / Despite of the well known advantages of steel fiber addition to concrete (SFRC), especially the toughness improvement, only a few number of studies has been developed about creep on these composites. The main purpose of this research is to investigate the feasibility and inherent difficulties related to a particular creep evaluation method. This method is based on beam test results and their analysis by fracture mechanics theory. It is intended to become an alternative method instead of the usual creep analysis of axial compression test results. At the same time, looking at the development of hybrid composites - made of distinct kind of fibers to obtain the best responses for micro and macrocracking - an experimental program was performed. Specimens molded with plain concrete, ordinary SFRC and hybrid SFRC were tested in flexure, the last one made of an association of short and large steel fibers. Characterization tests were performed to obtain the main mechanical properties of these materials at several ages. The mixture proportions were based in previous studies, where good performance characteristics were observed in hybrid composites. Nevertheless, in this particular test series, the addition of shorter steel fibers resulted in high air contents, what probably caused the decrease of the composite\'s performance in some aspects. The test results displayed low influence of the fiber addition on mechanical properties such compression strength, modulus of elasticity and tensile strength. Creep performance showed to be worse in the SFRC and hybrid composites than in plain concrete matrix. However, the reinforcement with steel fibers improved the shrinkage restrain. The analysis of the long-term beam deflections was made by finding the corresponding strains in the sections. Afterwards, specific creep functions were obtained by regression methods. The experimental creep functions were compared to the existing ones in literature and design codes. Despite of some differences, such as higher initial creep rate, higher creep coefficients and faster stabilization, it may be concluded that these functions represented quite well the phenomenon. Also experimental functions for plain concrete showed good results when compared to creep prediction model given by design codes, such as the Brazilian NBR 6118:2003 and ACI 209:1982. Comparison with numerical modeling results also gave satisfactory results. Creep in flexure was also evaluated by means of notched beam tests, where the sustained load was performed only by the beam self-weight. The test results were analyzed by numerical modeling and application of fracture mechanic concepts. The overall results showed the feasibility of creep assessing by the beam test method, which can be, after further detailed test series, a good alternative method instead of axial compression tests. Also dynamic free vibration tests were performed, according to ASTM C-215:1991 recommendations, to investigate the beam stiffness loss due to long term loading effects. These tests showed that modal analysis can be a helpful method in the tests, since it does not introduce damages in the test specimens.