No Brasil, o processo construtivo como um todo está modificado, assim como o cálculo estrutural e as técnicas gerenciais de construção. Algumas empresas que visam competitividade no mercado buscam soluções para aumentar a velocidade de suas obras, como redução do tempo de execução da estrutura, redução do período de escoramento e antecipação das alvenarias. A retirada antecipada do escoramento submete a estrutura de concreto a um carregamento precoce, sem que haja tempo de ocorrerem todas as reações de hidratação do cimento, podendo desencadear um processo de microfissuração. Dessa forma, o presente estudo avaliou o comportamento das propriedades mecânicas de concretos produzidos com quatro diferentes tipos de cimento (CPV ARI, CPV ARI RS, CPIV RS, CPII Z), quando submetidos a um carregamento precoce de compressão. Foram avaliados resultados de resistência à compressão, resistência à tração por compressão diametral, módulo de elasticidade, velocidade de onda ultra-sônica, condições de cura e ensaios de microscopia eletrônica de varredura. Procurou-se analisar o efeito de diferentes níveis de resistências com a produção de concretos com relações água/cimento de 0,35, 0,50 e 0,70, quando submetidos a um carregamento precoce em diferentes idades (1, 3 e 7 dias) e diferentes percentuais de carregamento (0%, 25%, 50% e 75%). Aos 28 dias foram ensaiados em suas propriedades especificadas. Os resultados mostraram que à medida que aumenta a idade de carregamento, as propriedades mecânicas são melhoradas para todos os cimentos. Por outro lado, quando se aplica os percentuais de pré-carregamento a resistência à compressão tende a aumentar, principalmente para o cimento CPV ARI. A análise de microscopia possibilitou a visualização de microfissuras causadas pelo pré-carregamento, assim como a recuperação das mesmas. Em relação aos outros cimentos foi observada uma queda nos valores de resistência à tração e no módulo de elasticidade. / In Brazil the building process as a role is modified, as well as structural design and building management techniques. The companies that aim competitiveness in the market are in search of solutions to increase the speed of their constructions, like reduction of structure execution time, reduction of support time and anticipated masonry execution. The anticipated remove of support submits the concrete structure to a premature load, carrying damage in cement hydration reaction, can unleash microcracking process. In this way, the present study evaluated the mechanical properties behavior of concretes produced with four different cements types (CPV ARI, CPV ARI RS, CPIV RS, CP IIZ), when submitted to premature compression load. The analysis included evaluation of the results of compressive strength, split tensile strength, modulus of elasticity, ultrasonic pulse velocity, cure conditions and scanning electron microscopic. The effect from different strengths levels with 0.35, 0.50 and 0.70 water/cement ratio, when submitted to a premature load in different ages (1, 3 and 7 days) and different percents of load (0%, 25%, 50% and 75% from rupture load) were analyzed. At The concrete with the age of 28 days was submitted to tests in order to specify its properties. The results showed that the mechanical properties of all cements improve as the age of load increases. In the other hand, when the preload area applied, the compressive strength tends to increase, mainly to CPV ARI cement. The microscopy analysis makes possibly the visualization of microcracking caused by preload, as well the recovering themselves. In the other cements were observed a small decrease in tensile strength and modulus of elasticity values.

No Brasil, o processo construtivo como um todo está modificado, assim como o cálculo estrutural e as técnicas gerenciais de construção. Algumas empresas que visam competitividade no mercado buscam soluções para aumentar a velocidade de suas obras, como redução do tempo de execução da estrutura, redução do período de escoramento e antecipação das alvenarias. A retirada antecipada do escoramento submete a estrutura de concreto a um carregamento precoce, sem que haja tempo de ocorrerem todas as reações de hidratação do cimento, podendo desencadear um processo de microfissuração. Dessa forma, o presente estudo avaliou o comportamento das propriedades mecânicas de concretos produzidos com quatro diferentes tipos de cimento (CPV ARI, CPV ARI RS, CPIV RS, CPII Z), quando submetidos a um carregamento precoce de compressão. Foram avaliados resultados de resistência à compressão, resistência à tração por compressão diametral, módulo de elasticidade, velocidade de onda ultra-sônica, condições de cura e ensaios de microscopia eletrônica de varredura. Procurou-se analisar o efeito de diferentes níveis de resistências com a produção de concretos com relações água/cimento de 0,35, 0,50 e 0,70, quando submetidos a um carregamento precoce em diferentes idades (1, 3 e 7 dias) e diferentes percentuais de carregamento (0%, 25%, 50% e 75%). Aos 28 dias foram ensaiados em suas propriedades especificadas. Os resultados mostraram que à medida que aumenta a idade de carregamento, as propriedades mecânicas são melhoradas para todos os cimentos. Por outro lado, quando se aplica os percentuais de pré-carregamento a resistência à compressão tende a aumentar, principalmente para o cimento CPV ARI. A análise de microscopia possibilitou a visualização de microfissuras causadas pelo pré-carregamento, assim como a recuperação das mesmas. Em relação aos outros cimentos foi observada uma queda nos valores de resistência à tração e no módulo de elasticidade. / In Brazil the building process as a role is modified, as well as structural design and building management techniques. The companies that aim competitiveness in the market are in search of solutions to increase the speed of their constructions, like reduction of structure execution time, reduction of support time and anticipated masonry execution. The anticipated remove of support submits the concrete structure to a premature load, carrying damage in cement hydration reaction, can unleash microcracking process. In this way, the present study evaluated the mechanical properties behavior of concretes produced with four different cements types (CPV ARI, CPV ARI RS, CPIV RS, CP IIZ), when submitted to premature compression load. The analysis included evaluation of the results of compressive strength, split tensile strength, modulus of elasticity, ultrasonic pulse velocity, cure conditions and scanning electron microscopic. The effect from different strengths levels with 0.35, 0.50 and 0.70 water/cement ratio, when submitted to a premature load in different ages (1, 3 and 7 days) and different percents of load (0%, 25%, 50% and 75% from rupture load) were analyzed. At The concrete with the age of 28 days was submitted to tests in order to specify its properties. The results showed that the mechanical properties of all cements improve as the age of load increases. In the other hand, when the preload area applied, the compressive strength tends to increase, mainly to CPV ARI cement. The microscopy analysis makes possibly the visualization of microcracking caused by preload, as well the recovering themselves. In the other cements were observed a small decrease in tensile strength and modulus of elasticity values.

This research aims to investigate the influence of 3D through-thickness stitching on the gas permeability and transverse microcracking of cryogenically cycled carbon/epoxy composites. 3D through-thickness stitching can be used to improve the interlaminar properties of polymer matrix composites (PMCs) and produce lightweight, unitized structures for cryogenic storage tanks. To fully utilize stitched composite structures for these applications, their inherent gas permeability challenges must be understood. Therefore, in this study, the stitched composites' damage evolution and gas permeability was experimentally characterized under a) pure thermal stress, b) thermal and uniaxial mechanical stress, and c) thermal and biaxial mechanical stress. Helium gas permeability was measured for each specimen at room or cryogenic temperatures under a mechanically strained state following the thermo-mechanical cycles. Optical microscopy was used to measure microcrack densities and monitor their evolution through the thickness of the composite specimens. Thin plies, graphene nanoplatelets (GNP) modified resin, and a hybrid barrier layer comprising of both were incorporated in the stitched specimens as barrier layers to reduce their gas permeability. The dependence of gas permeability of stitched composites on the mechanical strain, test temperature, and load history was evaluated and correlated to microcrack density. A significant reduction in permeability and damage evolution (transverse microcracks and delaminations) was obtained for all thermo-mechanical cases using the hybrid barrier layer laminate. Additionally, the permeability was several orders of magnitude lower than the allowable. Overall, the hybrid barrier layer shows tremendous promise as a viable barrier layer for stitched/unstitched composites undergoing thermo-mechanical fatigue involving a cryogenic environment.

The objective of this research was to measure and analyze the long-term modulus values of cement-treated base (CTB) layers constructed in Utah using microcracking. Because modulus values of pavement layers are among the most influential inputs affecting mechanistic-empirical pavement design, obtaining reasonable estimates of modulus values is critical. Testing was performed with a portable falling-weight deflectometer, also called a lightweight deflectometer, and modulus values were backcalculated with the computer program BAKFAA. Testing occurred at five asphalt pavement sites in northern Utah, where reconstruction with full-depth reclamation and cement stabilization, in the form of cement slurry, was performed approximately 2 to 14 years previously. Unconfined compressive strength (UCS) data collected for the CTB materials during earlier projects were compiled for all five sites. The correlation between backcalculated CTB modulus values, which ranged from 42 to 433 ksi, and 7-day UCS values, which ranged from 366 to 559 psi, was analyzed, and uniformity and sensitivity analyses were performed. Based on the results of this research, a new correlation is proposed for estimating the long-term modulus values of microcracked CTB layers constructed in a seasonally cold climate, such as northern Utah. For an average 7-day UCS of 450 psi, a CTB modulus value of 114 ksi would be estimated using this correlation, whereas a much higher modulus value of 630 ksi would be estimated from an existing correlation chart that was published in 1972 before microcracking was developed as a CTB construction practice. The results of the uniformity analyses indicate that statistically significant spatial variability in the CTB modulus values exists at each site. In comparison to a proposed maximum threshold coefficient of variation of 40 percent presented in the literature for aspects of CTB construction, the CTB modulus at all of the sites would be characterized as having low uniformity, with values ranging from 42.9 to 90.3 percent. The results of the sensitivity analyses indicate that backcalculated CTB modulus values are sensitive to typical deviations from design values that may occur in pavement layer thicknesses and suggest that CTB modulus estimation errors may range from -22,561 to 62,097 psi, or -3.73 to 10.81 percent, for pavements similar to those studied in this research when the actual asphalt and CTB layer thicknesses are different than the assumed values by up to 0.25 or 0.50 in., respectively.

This research develops two novel experimental techniques based on nonlinear acoustics/ultrasound to provide an ultra-accelerated characterization of alkali-reactivity of aggregates. Alkali-silica reaction (ASR) is a deleterious reaction occurring between reactive siliceous minerals present in some aggregates and alkalis mainly contributed by the cement, but also present in some deicing chemicals. With increasing reports of ASR-induced damage in transportation structures, there is a critical need for fast and reliable test methods for the screening of aggregates and aggregate/paste combinations. Currently, the accelerated mortar bar test (AMBT), which measures expansion, is the most commonly used test method. Also used is the concrete prism test (CPT), another expansion-based method, which requires at least one year testing time, limiting the practical utility of this method. In addition, petrographic analysis can be performed to identify potentially reactive minerals in aggregates but requires training and may not be appropriate for assessment of aggregate/paste combinations. Finally, linear acoustic methods such as wave speed and attenuation measurements can be used for the assessment of ASR, but the sensitivity of linear acoustic methods to ASR-induced damage is considered to be relatively low. Therefore, critical limitations exist in the existing test methods. In light of recent advances in nonlinear acoustics (which are more sensitive to small-scale damage than linear acoustics), the purpose of this research is the development and assessment of an accelerated method for evaluating the potential for alkali reactivity in aggregate and aggregate/paste combinations by combining advanced ultrasonic methods with standard test procedures. In fact, two nonlinear acoustic methods are developed under this research - nonlinear wave modulation spectroscopy (NWMS) and nonlinear impact resonance acoustic spectroscopy (NIRAS) - and are used to characterize the changes in material nonlinearity as a result of the progressive ASR damage during the standard mortar bar and concrete prism testing. Following the AMBT and CPT, nonlinear acoustic techniques are applied to both mortar bars and concrete prism samples. Nonlinearity parameters are defined as the indicator of growing ASR damage, and measurement results clearly show that these nonlinearity parameters are more sensitive to the ASR damage than the linear parameters used in the linear acoustic measurements, particularly at early ages. Different aggregates with varying alkali-reactivity are effectively distinguished with the proposed experimental techniques in a timely manner, particularly for those aggregates with similar levels of reactivity, as determined by AMBT. The effect of a Class C fly ash addition on nonlinear properties was also investigated using the NIRAS measurements through a comparison of test results between mortar samples blended with fly ash and without fly ash. As complementary supports of the experimental results, petrographic analyses and theoretical modeling are also performed, and these results are well correlated with results from the NWMS and NIRAS techniques. Through a comparison with results from accompanying expansion measurements and linear acoustic methods, the proposed nonlinear acoustic techniques show their advantages to accelerate the assessment of alkali-reactivity of aggregates. Under AMBT, reactive aggregates were identifiable as early as a few days of testing. With CPT, reactive aggregates were differentiated as early as a few weeks. Overall, the coupling of the developed nonlinear test methods with standard expansion tests suggests that test durations could be potentially reduced by half, especially for AMBT tests.

The objective of this research was to analyze the strength and deformation characteristics of a cement-treated base (CTB) constructed using full-depth reclamation, microcracked, and then surfaced with a single chip seal. In this field study, strength characteristics of the CTB layer were determined at the time of construction, and then both strength and deformation characteristics were evaluated after 9 months of low-volume, heavy truck traffic. After 9 months, observed distresses included transverse cracking, rutting, and chip seal joint failure. The loss of the chip seal was caused by poor chip seal construction practices and not a deficiency in the CTB layer. The importance of the role of the chip seal as a wearing course was made evident by these failures since the exposed CTB often exhibited material loss. The average ride qualities in and out of the wheel path were in the fair ride category; the roughness was not likely caused by trafficking but probably resulted from construction or climatic factors. Structural testing performed after 9 months of service indicated that the CTB stiffness and modulus were greater than the values measured after microcracking at the time of construction, indicating continued strength gain. However, trafficking over the 9-month period had caused significantly lower stiffnesses measured in the wheel paths than between the wheel paths. The average unconfined compressive strength (UCS) of the cores tested at 9 months was not significantly different than the average UCS of the field-compacted specimens tested at 6 weeks. Based on the observed performance of the CTB and chip seal evaluated in this research, recommendations for improved CTB performance include the use of a thicker and/or stiffer CTB layer, ensuring a smooth CTB surface during construction, and application of a double chip seal or equivalent.

Estudos experimentais realizados por alguns autores abordaram os mecanismos de deformação nas gipsitas, tais como o fluxo plástico e a dissolução por pressão. Ainda assim, é pequeno o conhecimento do comportamento mecânico das rochas de gipso. Nesta tese foram estudados os mecanismos de deformação lenta em gipsitas bandadas da Formação Santana da Chapada de Araripe com uso da técnica de emissão acústica. Adotou-se este procedimento como técnica indireta de detecção do processo de microfissuramento, para evitar mudanças que ocorrem na microestrutura durante seu descarregamento e preparação de amostras para sua observação por técnicas diretas. Realizaram-se ensaios de fluência de curto e longo prazo numa prensa hidráulica servocontrolada MTS 815 e em conjunto modulares (torres individuais) em um laboratório de fluência especialmente equipado. Encontrou-se que o mecanismo do microfissuramento está fortemente influenciado por processos de cicatrização durante ensaios de fluência de longo prazo. Devido ao processo de cicatrização da microfissura, a fluência terciaria nunca foi alcançada, mesmo em corpos de prova carregados com até 95% da resistência à compressão uniaxial. Nesta tese outros resultados importantes foram alcançados como: identificar que o fenômeno de microfissuramento para a rocha em questão é detectado por fenômenos de emissão acústica de freqüências intermediárias (de 100 a 400 kHz) e constatar que o efeito Kaiser se manifesta neste tipo de rochas de modo inequívoco para solicitações rápidas, enquanto após ensaios de fluência de longa duração, não mais se manifesta, por causa da cicatrização. Ou seja, corpos de prova submetidos mais uma vez à compressão uniaxial após o descarregamento, voltam a apresentar eventos de emissão acústica e, conseqüentemente, a geração de novas microfissuras. Este fato somente pode ser explicado por um processo de cicatrização da microfissura durante a fluência de longo prazo. Esta cicatrização, devido a fenômenos físico-químicos, apresentou outros indícios como um aumento no módulo de elasticidade após ensaios de fluência, quando comparado aos valores antes do ensaio, e mesmo um endurecimento (aumento da resistência à compressão uniaxial) também após a fluência. Esclareceu-se também de modo inequívoco que o descarregamento provoca o progresso do microfissuramento. Além dos sinais característicos do microfissuramento, constatou-se que o módulo de elasticidade, medido nos mesmos níveis de tensão, é mais alto antes que depois do descarregamento. O decréscimo de rigidez é indício do processo de dano por microfissuramento. / Experimental studies by several authors have shown some of the key deformation mechanisms in gypsum, such as plastic flow and pressure dissolution. Even so, there is still sparse knowledge about the mechanical behavior of natural gypsum rocks. Creep mechanisms of the banded gypsum rock of Santana Formation from the Chapada do Araripe (Santana Formation) in creep tests were studied with acoustic emission technique correlating the stress levels related to microcracking to the energy release associated with these mechanisms. This procedure was adopted as an indirect technique of detection of the microcracking process, to prevent changes that occur in the microstructure during unloading and in sample preparation for its observations with direct techniques. Short and long-term creep tests were carried out in an MTS 815 servo-controlled testing system and in modular sets (single towers) in a specially equipped creep laboratory. It was found that the microcrack mechanism is strongly influenced by healing processes during long-term creep. Due to the microcrack healing process, tertiary creep was never reached, even in specimens loaded with up to 95% of the uniaxial compressive strength. In this thesis other important results were reached as: to identify that the microcracking phenomenon for the rock in question is detected by acoustic emission phenomena of intermediate frequencies (from 100 to 400 kHz) and to evidence that the Kaiser effect unequivocally manifests in this type of rock when subjected to quick loads, while after long-term creep tests, it is no longer evidenced on account of healing. In other words, the specimens subjected once again to uniaxial compression after unloading, again show acoustic emission events and therefore the generation of new microcracks. This fact can only be explained by a microcrack healing process during long-term creep. This healing, due to physical-chemical phenomena, presented other indications as an increase in the modulus of elasticity after creep tests, when compared to the values before the test, and even a hardening (increase of the uniaxial compressive strength) also after the creep. It was also clarified in unequivocal way that the unloading provokes microcracking progress. In addition to the microcracking characteristic indications, it was found that the modulus of elasticity, when measured at the same stress levels, is higher before unloading than after the unloading. The stiffness decrease is indication of the microcracking damage process.

No description available.

Le matériau composite agrégataire énergétique étudié a un comportement viscoélastique endommageable sensible à la pression de confinement et à la température. Ces travaux concernent la modélisation de l'anisotropie induite par endommagement avec deux objectifs principaux. Dans un premier temps, le caractère anisotrope de l'endommagement est mis en évidence expérimentalement. Des essais alternant tension et compression permettant d'observer l'effet unilatéral d'endommagement. Ensuite, un modèle de comportement est développé pour le matériau d'étude. Des modèles pertinents sont tout d'abord comparés. Le modèle le plus approprié est ensuite amélioré par l'ajout de mécanismes d'endommagement, d'effectivité du dommage et d'un mécanisme de plasticité. Les données expérimentales sont utilisées pour identifier les paramètres du modèle. Ce dernier a été ensuite implémenté dans un logiciel de calcul aux éléments finis (Abaqus / standard) sous la forme d'une procédure Fortran (UMAT). Différents types de chargements sont simulés et confrontés aux résultats expérimentaux. / An explosive aggregate material exhibits a visco-elastic behaviour with damage, internal friction and sensitivity to the confining pressure and temperature. This thesis focuses on the anisotropic elastic damage with unilateral effect. The first aim of this study is to highlight experimentally the anisotropic nature of the damage. Then, a new model is proposed for the studied material. This is achieved using a comparison of some relevant models in order to select the most appropriate among them. The selected model is then improved by adding unilateral effect mechanisms and plasticity. Experimental data is used to characterize the material behaviour and to determine the parameters of improved model. This model has been implemented in the finite element software (Abaqus / Standard) using Fortran procedure (UMAT) and then tested for different loads and compared with experimental results.

Estudos experimentais realizados por alguns autores abordaram os mecanismos de deformação nas gipsitas, tais como o fluxo plástico e a dissolução por pressão. Ainda assim, é pequeno o conhecimento do comportamento mecânico das rochas de gipso. Nesta tese foram estudados os mecanismos de deformação lenta em gipsitas bandadas da Formação Santana da Chapada de Araripe com uso da técnica de emissão acústica. Adotou-se este procedimento como técnica indireta de detecção do processo de microfissuramento, para evitar mudanças que ocorrem na microestrutura durante seu descarregamento e preparação de amostras para sua observação por técnicas diretas. Realizaram-se ensaios de fluência de curto e longo prazo numa prensa hidráulica servocontrolada MTS 815 e em conjunto modulares (torres individuais) em um laboratório de fluência especialmente equipado. Encontrou-se que o mecanismo do microfissuramento está fortemente influenciado por processos de cicatrização durante ensaios de fluência de longo prazo. Devido ao processo de cicatrização da microfissura, a fluência terciaria nunca foi alcançada, mesmo em corpos de prova carregados com até 95% da resistência à compressão uniaxial. Nesta tese outros resultados importantes foram alcançados como: identificar que o fenômeno de microfissuramento para a rocha em questão é detectado por fenômenos de emissão acústica de freqüências intermediárias (de 100 a 400 kHz) e constatar que o efeito Kaiser se manifesta neste tipo de rochas de modo inequívoco para solicitações rápidas, enquanto após ensaios de fluência de longa duração, não mais se manifesta, por causa da cicatrização. Ou seja, corpos de prova submetidos mais uma vez à compressão uniaxial após o descarregamento, voltam a apresentar eventos de emissão acústica e, conseqüentemente, a geração de novas microfissuras. Este fato somente pode ser explicado por um processo de cicatrização da microfissura durante a fluência de longo prazo. Esta cicatrização, devido a fenômenos físico-químicos, apresentou outros indícios como um aumento no módulo de elasticidade após ensaios de fluência, quando comparado aos valores antes do ensaio, e mesmo um endurecimento (aumento da resistência à compressão uniaxial) também após a fluência. Esclareceu-se também de modo inequívoco que o descarregamento provoca o progresso do microfissuramento. Além dos sinais característicos do microfissuramento, constatou-se que o módulo de elasticidade, medido nos mesmos níveis de tensão, é mais alto antes que depois do descarregamento. O decréscimo de rigidez é indício do processo de dano por microfissuramento. / Experimental studies by several authors have shown some of the key deformation mechanisms in gypsum, such as plastic flow and pressure dissolution. Even so, there is still sparse knowledge about the mechanical behavior of natural gypsum rocks. Creep mechanisms of the banded gypsum rock of Santana Formation from the Chapada do Araripe (Santana Formation) in creep tests were studied with acoustic emission technique correlating the stress levels related to microcracking to the energy release associated with these mechanisms. This procedure was adopted as an indirect technique of detection of the microcracking process, to prevent changes that occur in the microstructure during unloading and in sample preparation for its observations with direct techniques. Short and long-term creep tests were carried out in an MTS 815 servo-controlled testing system and in modular sets (single towers) in a specially equipped creep laboratory. It was found that the microcrack mechanism is strongly influenced by healing processes during long-term creep. Due to the microcrack healing process, tertiary creep was never reached, even in specimens loaded with up to 95% of the uniaxial compressive strength. In this thesis other important results were reached as: to identify that the microcracking phenomenon for the rock in question is detected by acoustic emission phenomena of intermediate frequencies (from 100 to 400 kHz) and to evidence that the Kaiser effect unequivocally manifests in this type of rock when subjected to quick loads, while after long-term creep tests, it is no longer evidenced on account of healing. In other words, the specimens subjected once again to uniaxial compression after unloading, again show acoustic emission events and therefore the generation of new microcracks. This fact can only be explained by a microcrack healing process during long-term creep. This healing, due to physical-chemical phenomena, presented other indications as an increase in the modulus of elasticity after creep tests, when compared to the values before the test, and even a hardening (increase of the uniaxial compressive strength) also after the creep. It was also clarified in unequivocal way that the unloading provokes microcracking progress. In addition to the microcracking characteristic indications, it was found that the modulus of elasticity, when measured at the same stress levels, is higher before unloading than after the unloading. The stiffness decrease is indication of the microcracking damage process.