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No. of bitstreams: 1 Dissertação-Cristiano P e Silva.pdf: 2768387 bytes, checksum: 2918349c69f33356b77eef93c4a83a6b (MD5) Previous issue date: 2015-02-06 / Não Informada / After completing the tooth bleaching, reaction products remain in the tooth structure not allowing the correct polymerization of adesives restorations. The purpose of this study was to investigate the antioxidants effects of sodium ascorbate hydrogel on the residual oxygen in the bovine enamel structure bleached with hydrogen peroxide and after restorated with composite resin. One hundred and twenty bovines teeth were divided into twelve groups (n: 10), the groups G1;G2;G3;G4;G5;G6 were subjected to a test of shear strength after one week, the groups G7;G8;G9;G10;G11;G12 were tested after six months (aged), being G1; G7 - restored without bleaching ; G2; G8 - bleached and restored after fourteen days; G3; G9 - bleached and restored at the same day; G4; G10 - bleached, treated with sodium ascorbate hydrogel of 10% and restored; G5; G11 - bleached, treated with sodium ascorbate hydrogel of 20% and restored and G6; G12 - bleached, treated with sodium ascorbate hydrogel of 40% and restored. The results of the shear test were subjected to two ANOVA’s criteria and Tukey's analysis to compare the scores (p≤ 0,05). The groups G1: 152,6N +- 21,2; G2: 183,2N +- 31,4; G5: 171,53N +- 20,6; G6: 179,9N +- 33,1 showed similar resistance to shear and the groups G3: 99,3N +- 33,9; G4: 101,3N +- 29,3 were statistically significant lower resistance. The second group had lower shear resistance, however maintained the same pattern of statistical difference between the groups. The aged groups G7: 98,1 +- 22,6; G8: 111,9 +- 34,0; G11: 91,9 +- 24,0; G12: 90,0 +- 13,1 showed lower shear resistance when compared to the non-aged. However, when compared between the aged, as well as between no-aged, the groups G9: 59,3 +- 19,9; G10: 59,7 +- 10,9 also showed lower resistance when compared to the others groups. We can conclude that the tooth bleaching with 35% hydrogen peroxide promoted reduction of the bond strength. In addition, treatment of the bleached enamel with 20% and 40% sodium ascorbate hydrogel allowed to reach values of bond strength similar of the enamel not bleached. / Após finalizar o tratamento de clareamento dentário os subprodutos da reação permanecem na estrutura dentária impedindo a correta polimerização das restaurações adesivas. O objetivo deste trabalho foi investigar os efeitos antioxidantes do hidrogel de ascorbato de sódio sobre o oxigênio residual na estrutura de esmalte bovino clareado com peróxido de hidrogênio e posteriormente restaurado com resina composta. Cento e vinte dentes bovinos foram divididos em 12 grupos (n=10), os grupos G1;G2;G3;G4;G5;G6 foram submetidos ao teste de cisalhamento após uma semana, os grupos G7;G8;G9;G10;G11;G12 foram testados após seis meses (envelhecimento), sendo G1;G7 - restaurado sem clareamento; G2;G8 - clareado e restaurado após 14 dias; G3;G9 - clareado e restaurado no mesmo dia; G4;G10 - clareado, tratado com hidrogel de ascorbato de sódio 10% e restaurado; G5;G11 - clareado, tratado com hidrogel de ascorbato de sódio a 20% e restaurado e G6;G12 - clareado, tratado com hidrogel de ascorbato de sódio a 40% e restaurado. Os resultados do teste de cisalhamento foram submetidos a ANOVA a 2 critérios e teste de Tukey para comparação das medias (p≤ 0,05). Os grupos G1: 152,6N +-­‐ 21,2; G2: 183,2N +-­‐ 31,4; G5: 171,53N +-­‐ 20,6; G6: 179,9N +-­‐ 33,1 apresentaram resistência ao cisalhamento semelhante e os grupos G3: 99,3N +-­‐ 33,9; G4: 101,3N +-­‐ 29,3 apresentaram resistência inferior estatisticamente significativa. O segundo grupo apresentou menor resistência ao cisalhamento porém, mantive o mesmo padrão de diferença estatística entre os grupos. Os grupos envelhecidos G7: 98,1N +- 22,6; G8: 111,9N +- 34,0; G11: 91,9N +- 24,0; G12: 90,0N +- 13,1 apresentaram menor resistência ao cisalhamento quando comparados aos não envelhecidos. No entanto, quando comparado entre os envelhecidos, assim como nos não envelhecidos, os grupos G9: 59,3N +- 19,9; G10: 59,7N +- 10,9 também apresentaram resistência inferior comparado aos demais grupos. Podemos concluir que o clareamento dental com o peróxido de hidrogênio a 35% promoveu redução da resistência adesiva. Além disso, o tratamento do esmalte clareado com hidrogel de ascorbato de sódio a 20% e a 40% permitiu alcançar valores de resistência de união similar ao esmalte não clareado.

A utilização da madeira laminada colada (MLC) é uma alternativa viável para o aproveitamento de todo o potencial da madeira, apresentando uma série de vantagens. A ligação entre as lâminas, no entanto, tem papel fundamental para a boa qualidade de peças de MLC. Portanto, para um bom desempenho de estruturas de MLC, é fundamental a escolha de um adesivo com boa resistência mecânica e resistência à ação do intemperismo. Os adesivos comumente utilizados, além de terem alto custo, que chega a 60% do custo total da MLC, contêm solventes que são nocivos à saúde, além de terem coloração escura, o que mancha a madeira. O custo baixo é primordial no sentido de tornar esse material mais viável e competitivo quando comparado com outros materiais. Assim, esse trabalho teve como objetivo verificar a capacidade de carga ao cisalhamento no plano de cola de corpos de prova preparados com um adesivo sem solvente e contribuir para a melhoria de eficiência de vigas laminadas coladas. Foram verificados os efeitos da pressão de colagem (1,25; 2,50 e 5,00 MPa), da temperatura (27, 60 e 90°C) e do tempo de cura do adesivo (7 e 10 dias) na tensão no limite de resistência ao cisalhamento. A dose de adesivo utilizada foi de 200 g/m2. Numa segunda etapa foram obtidas a massa específica e a umidade das amostras já ensaiadas ao cisalhamento a fim de explicar a variabilidade dos resultados encontrados. A madeira utilizada para a confecção das peças foi o Eucalyptus grandis por ser uma espécie de grande potencial para usos múltiplos e porque suas propriedades físicomecânicas o tornam adequado também para fim estrutural. Concluiu-se que a temperatura de 90°C possibilitou os melhores valores de tensão de cisalhamento. A pressão de colagem e o tempo de cura do adesivo não influenciaram nessa importante propriedade mecânica. / The use of glu-lam is a viable alternative for exploitation of all wood potential presenting a series of advantages. The linking between layers however has a basic paper in glu-lam good quality. Therefore for a good performance of glu-lam structures it is fundamental the choice of an adhesive which has a great mechanics resistance and also resistance to the weather action. The adhesives usually used having high cost, that arrives 60% of glu-lam total cost beyond contain solvent that are harmful to health, having dark coloration what changes the wood natural color. Low cost is primordial to become this material more viable and competitive if compared with another materials. Thus, this search had as objective to verify the load capacity applied in the samples in shear strength test right in the glued surface and also contributing for efficiency improvement of beam-glu-lam. The glue used to prepare the samples was free of solvent. It were verified the effect of gluing pressure (1,25; 2,50 e 5,00 MPa), temperature (27, 60 e 90°C) and the adhesive time of cure (7 and 10 days)in the shear strength. The adhesive dose applied in the layers was 200g/cm2.In a second research step it were obtained the specific gravity and moisture content from the samples which were already tested to explain the variability that was observed. It was utilized Eucalyptus grandis wood for being a specie of enormous potential for multi purpose and because its physical and mechanical properties make it. Highest values of shear strength were obtained at the temperature of 90°C. The glue pressure and the adhesive curing time have no relevant influence on this important mechanical properties.

A utilização da madeira laminada colada (MLC) é uma alternativa viável para o aproveitamento de todo o potencial da madeira, apresentando uma série de vantagens. A ligação entre as lâminas, no entanto, tem papel fundamental para a boa qualidade de peças de MLC. Portanto, para um bom desempenho de estruturas de MLC, é fundamental a escolha de um adesivo com boa resistência mecânica e resistência à ação do intemperismo. Os adesivos comumente utilizados, além de terem alto custo, que chega a 60% do custo total da MLC, contêm solventes que são nocivos à saúde, além de terem coloração escura, o que mancha a madeira. O custo baixo é primordial no sentido de tornar esse material mais viável e competitivo quando comparado com outros materiais. Assim, esse trabalho teve como objetivo verificar a capacidade de carga ao cisalhamento no plano de cola de corpos de prova preparados com um adesivo sem solvente e contribuir para a melhoria de eficiência de vigas laminadas coladas. Foram verificados os efeitos da pressão de colagem (1,25; 2,50 e 5,00 MPa), da temperatura (27, 60 e 90°C) e do tempo de cura do adesivo (7 e 10 dias) na tensão no limite de resistência ao cisalhamento. A dose de adesivo utilizada foi de 200 g/m2. Numa segunda etapa foram obtidas a massa específica e a umidade das amostras já ensaiadas ao cisalhamento a fim de explicar a variabilidade dos resultados encontrados. A madeira utilizada para a confecção das peças foi o Eucalyptus grandis por ser uma espécie de grande potencial para usos múltiplos e porque suas propriedades físicomecânicas o tornam adequado também para fim estrutural. Concluiu-se que a temperatura de 90°C possibilitou os melhores valores de tensão de cisalhamento. A pressão de colagem e o tempo de cura do adesivo não influenciaram nessa importante propriedade mecânica. / The use of glu-lam is a viable alternative for exploitation of all wood potential presenting a series of advantages. The linking between layers however has a basic paper in glu-lam good quality. Therefore for a good performance of glu-lam structures it is fundamental the choice of an adhesive which has a great mechanics resistance and also resistance to the weather action. The adhesives usually used having high cost, that arrives 60% of glu-lam total cost beyond contain solvent that are harmful to health, having dark coloration what changes the wood natural color. Low cost is primordial to become this material more viable and competitive if compared with another materials. Thus, this search had as objective to verify the load capacity applied in the samples in shear strength test right in the glued surface and also contributing for efficiency improvement of beam-glu-lam. The glue used to prepare the samples was free of solvent. It were verified the effect of gluing pressure (1,25; 2,50 e 5,00 MPa), temperature (27, 60 e 90°C) and the adhesive time of cure (7 and 10 days)in the shear strength. The adhesive dose applied in the layers was 200g/cm2.In a second research step it were obtained the specific gravity and moisture content from the samples which were already tested to explain the variability that was observed. It was utilized Eucalyptus grandis wood for being a specie of enormous potential for multi purpose and because its physical and mechanical properties make it. Highest values of shear strength were obtained at the temperature of 90°C. The glue pressure and the adhesive curing time have no relevant influence on this important mechanical properties.

A utilização de solo natural misturado com bentonita empregado em camadas impermeáveis para retenção de contaminante é bastante comum em aterros sanitários. Neste trabalho, serão apresentados os resultados de ensaios com misturas de solo-bentonita nos teores de 3%, 5% e 7%, utilizando-se um solo arenoso proveniente da região de Pindorama (SP). Os ensaios de condutividade hidráulica para o solo-bentonita foram realizados em permeâmetros de parede flexível. Os resultados obtidos indicam que para os teores de 5% e 7% de bentonita a condutividade hidráulica apresenta-se com valores adequados para a construção de barreiras impermeáveis. A resistência ao cisalhamento do solo compactado puro e das misturas compactadas foi avaliada através de ensaios triaxiais do tipo consolidado não drenado (CU) e ensaios de compressão simples. A coesão efetiva e o ângulo de atrito efetivo do solo aumentou e diminuiu, respectivamente, com a adição de bentonita. Os ensaios de resistência à compressão simples para as misturas com 5% de bentonita atingiram valores aceitáveis para o emprego em camadas impermeabilizantes. / It is becoming very common the use of soil-bentonite mixtures for building sanitary landfill liners with the purpose of retaining pollutants. This work shows the results of hydraulic conductivity and shear strength tests performed with soil-bentonite mixtures with 3%, 5% and 7% bentonite content. The natural soil was gathered in the Pindorama area, which is located in the northeast of Sao Paulo state. The hydraulic conductivity tests were performed in a flexible wall permeameter. Test results show that mixtures with 5% and 7% bentonite content are suitable, in terms of hydraulic conductivity, for construction of sanitary landfill liners. The shear strength parameters of natural soil and mixtures have been assessed performing undrained triaxial compression tests and unconfined compression tests. The effective cohesion and the effective friction angle increased and decreased with the increase of the bentonite content, respectively. The unconfined compression test results have shown that mixtures with 5% bentonite content are suitable, in terms of shear strength, for construction of sanitary landfill liners.

No description available.

Shallow foundations are extensively used to support structures of all sizes and derive their support from near surface soils. Thus, they are typically embedded up to a few meters into the soil profile. Designers of shallow foundations are required to meet two limit states: overall failure of the soil beneath the foundation (bearing capacity) and excessive settlement. Existing bearing capacity design methods use an assumed shearing plane within the soil and perfectly plastic soil behavior to estimate the ultimate resistance available. The immediate settlement of a shallow foundation is typically approximated using an elasticity-based method that does not account for actual, nonlinear soil behavior. A load test database was developed from footing load tests reported in the literature to assess the accuracy and uncertainty in existing design methodologies for calculating bearing capacity and immediate settlement. The assessment of uncertainty in bearing capacity and immediate settlement was accomplished through the application of a hyperbolic bearing pressure-displacement model, and the adaptation of the Duncan-Chang soil constitutive model to footing displacements. The prediction of bearing capacity using the general bearing capacity formula was compared to the bearing capacity extrapolated from the load test database using a hyperbolic bearing pressure-displacement model. On average the general bearing capacity formula under-predicts the bearing capacity and exhibits a significant amount of variability. The comparison was used to develop resistance statistics that were implemented to produce resistance factors for an LRFD based design approach using AASHTO load statistics. The Duncan-Chang model was adapted to predict bearing pressure displacement curves for footings in the load test database and used to estimate governing soil parameters. Bearing pressure-displacement curves fitted to the observed curves were used to back calculate soil stiffness. The soil stiffness was used with an elasticity-based displacement prediction method to evaluate the accuracy of the method. Finally, the back-calculated modulus from the fitted Duncan-Chang model was used to assess the accuracy and uncertainty associated with the elasticity-based K-factor, a correlation based stiffness parameter. In general the comparisons indicate that the current design procedures over-predict the bearing pressure associated with a given displacement and exhibit a significant amount of uncertainty. / Graduation date: 2012

The gluing of unseasoned wood, called green gluing, is a relatively new sawmill process, implying a radically changed order of material flow in the production of value-added wood-based products. It facilitates the enhancement of raw material recovery and value yield by integrating defect elimination and gluing already before kiln drying. The present study evaluates green glued adhesive bonds in flatwise glued beams and finger joints. The main part of this work deals with green gluing using a moisture curing polyurethane adhesive (PUR). Standardised test methods and specially designed, small scale, specimens were used for the determination of the strength, fracture energy and the ductility of both dry- and green glued bonds in tension and in shear. Using the small scale specimens it was possible to capture the complete stress versus deformation curves, including also their unloading part. An optical system for deformation measurement was used for the analysis of bond behaviour. The influence of moisture content during curing and temperature after curing on the adhesive chemical composition and on the mechanical properties was investigated. Furthermore, the moisture transport through the adhesive bond during curing was tested. Finally, microscopy studies were performed for analysis of bond morphology and fracture. The results show that two significant factors influence the shear strength of green glued bonds: wood density and adhesive spread rate. Bonds which fulfil the requirements according to EN 386 could be obtained within a wide range of process parameters. The small specimen tests showed that green glued PUR bonds can reach the same strength and fracture energy, both in shear and in tension, as dry glued bonds with the same adhesive amount. The local material properties of the bonds could be determined, thanks to the failure in the tests taking place within the adhesive bond itself and not in the wood. Following process factors were shown to cause lower bond strength: a) a low adhesive spread rate, b) high pressure and c) short pressing time in combination with low wood density and high moisture content. Moreover, the heat treatment of the cured PUR adhesive during drying influenced the chemical composition of the adhesive, providing for higher strength, stiffness and Tg of the adhesive, caused by an increased amount of highly ordered bidentate urea.

The surface roughness of unfilled rock discontinuities has a major influence on the hydro-mechanical behaviour of discontinuous rock masses. Although it is widely recognized that surface roughness is comprised of large-scale (waviness) and small-scale (unevenness) components, most investigations of surface roughness have been restricted to small fracture surfaces (<1m2). Hence, the large-scale components of roughness are often neglected. Furthermore, these investigations typically define roughness using two-dimensional profiles rather than three-dimensional surfaces, which can lead to biased estimates of roughness. These limitations have led to some contradictory findings regarding roughness scale effects. This thesis aims to resolve some of these issues. The main findings indicate that discontinuity roughness increases as a function of the sampling window size contrary to what is commonly assumed. More importantly, it is shown that the estimated roughness significantly decreases as the resolution of surface measurements decrease, which could lead to the under estimations of roughness and, consequently, discontinuity shear strength.

Geomembranes are one of the most widely used geosynthetics in various civil engineering applications. Their primary function is as a barrier to liquid or vapour flow. Smooth Geomembranes are frequently used in combination with different soils, and due to their low surface roughness, are challenging to design to ensure adequate shear strength along the smooth geomembrane-soil interface. It is important to use the appropriate values of interface shear strength parameters in the design of slopes incorporating one or more geomembranes in contact with soils. The parameters are determined by conducting direct shear test on the geomembrane-soil interface. Laboratory tests of interface shear strength for geomembranes and soil are typically carried out with no provision for measurement of pore pressures at the soil/geomembrane interface. <p>This thesis deals with study of smooth geomembrane-soil interfaces, particularly under unsaturated conditions. The various factors that affect the interface shear behaviour are also studied. The tests were conducted using a modified direct shear box with a miniature pore pressure transducer installed adjacent to the surface of the geomembrane. Geomembranesoil interface shear tests were carried out with continuous measurement of suction in close proximity to the interface during the shearing process thus making it possible to analyze test results in terms of effective stresses. The method was found to be suitable for unsaturated soils at low values of matric suction. <p>Results of interface shear tests conducted using this method show that it is quite effective in evaluating interface shear behaviour between a geomembrane and an unsaturated soil. The results suggest that soil suction contributes to shearing resistance at low normal stress values. At lower normal stress values, the interface shear behaviour appears to be governed only by the magnitude of total normal stress. <p> At high normal stresses, the failure mechanism changed from soil particles sliding at the surface of geomembrane to soil particles getting embedded into the geomembrane and plowing trenches along the direction of shear. A plowing failure mechanism resulted in the mobilization of significantly higher shear strength at the geomembrane soil interface. It was found that placement water contents near saturated conditions results in lower effective stresses, a shallower plowing mechanism and lower values of mobilized interface shear strength.

Forest soils with low bulk densities are often considered less susceptible to compaction than soils with higher bulk densities. The objective of this study was to determine if soil strength controlled the compression of soils with low bulk density. Four soils were selected for this evaluation. Three of these were andic soils with low bulk density and the fourth soil was a more dense, cohesive soil. Undisturbed samples of saturated and partly saturated soil were compressed in a one-dimensional consolidation test apparatus. Measurements with separate samples were at one of 7 normal stresses between 0.033 and 1.96 MPa. Shear strength of saturated soil was measured in direct shear tests. Primary consolidation of saturated soil was completed in less than one minute at all normal stresses. Shear stress and bulk density increased continuously during shear strain. The compression index of the cohesive soil was significantly larger (p<0.05) than that of the andic soils. The shear strength of andic soils (average cohesion intercept of 0.016 MPa and friction angle of 33.3°) was significantly higher (p<0.05) than the cohesive soil (cohesion intercept of 0.028 MPa and friction angle of 28.9°). When saturated, the cohesive soil was more compressible than the andic soils because of lower soil strength. A nonlinear model of soil compression was developed that accurately predicted the compressed density of saturated and partly saturated soil as a function of normal stress, initial bulk density of undisturbed samples, and degree of saturation. As degree of saturation decreased, the compressibility of the cohesive soil decreased more rapidly than it did for the andic soils. As a result, bulk density of dry cohesive soil increased less than it did for dry andic soils. Differences in the compressibility of soils were attributed to texture and clay mineralogy. The differences in the compressibility of these soils were much smaller than were the differences in bulk density. Decreasing water content affected the compressibility of the cohesive soil more than it affected the andic soils. Because soil strength controls the compressibility of these forest soils regardless of bulk density, it will also determine the susceptibility of soils to compaction by machines. / Graduation date: 1991