• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 744
  • 228
  • 217
  • 96
  • 62
  • 49
  • 35
  • 35
  • 35
  • 35
  • 35
  • 34
  • 20
  • 12
  • 9
  • Tagged with
  • 1823
  • 921
  • 231
  • 214
  • 213
  • 173
  • 167
  • 122
  • 102
  • 93
  • 92
  • 87
  • 86
  • 84
  • 79
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
971

Degradabilidade de grãos secos e ensilados de sorgo, com e sem tanino, submetidos à granulometrias

Souza, Carla Giselly de [UNESP] 26 May 2009 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:26:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-05-26Bitstream added on 2014-06-13T20:14:31Z : No. of bitstreams: 1 souza_cg_me_botfmvz.pdf: 278641 bytes, checksum: 2c6856fd3f09ad74fc57c4c34c33e6c0 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Universidade Estadual Paulista (UNESP) / O objetivo desse trabalho foi avaliar o efeito da granulometria (moagem) nos grãos de dois híbridos de sorgo (com e sem tanino), conservados secos ou ensilados úmidos, sobre a degradabilidade in situ da matéria seca (MS) e proteína bruta (PB) em ovinos. Foram utilizados três ovinos adultos, fistulados no rúmen, distribuídos em um delineamento experimental em blocos, com arranjo fatorial de 2 x 2 x 3 , sendo dois híbridos de sorgo (com e sem tanino), duas formas de conservação (seco e ensilado), três granulometrias (inteiro, moído grosso e moído fino), e o tempo como sub parcela. Recomenda-se a moagem dos grãos de sorgo, pois proporciona aumento da degradabilidade ruminal e efetiva da matéria seca, proteína bruta e amido. A presença do tanino no grão de sorgo alterou a degradabilidade potencial da proteína bruta e amido. Pelos resultados inferidos recomenda-se a moagem dos grãos de sorgo, por aumentar a degradabilidade ruminal e efetiva da matéria seca, proteína bruta e amido. O melhor tratamento foi a moagem grossa no grão sem tanino armazenado na forma de grãos secos. / The main research purpose was evaluate the grinding effect on two sorghum genotypes grain with and without tannin, in dry grain or humid silage conservation above the dry matter in situ degradability and crude protein. Three rumen fistulated sheep was used, in a bloc design, in a 2 x 2 x 3 factorial out line, with two sorghum genotypes (with and without tannin), two conservation ways (dry grain and high moisture grains silage) and three grinding ways (role, thick grinding and fine grinding) and time like sub-portion. To sorghum grains is recommended the grinding just because increases the dry matter and crude protein, ruminal and effective degradability. The tannins presence depressed the crude protein effective degradability, in a soft way. The fine grinding became a huge increasing in dry matter degradability rate. In this way the better treatment was the fine grinding without tannin in dry grain. We recommend the grinding, to sorghum grains independent the conservation way or utilized genotype, just because increase the ruminal and effective ruminal degradability. Mainly to without tannin genotype in dry grain way.
972

Sistema de supervisão e controle de irrigação utilizando técnicas de inteligência artificial

Fontes, Ivo Reis [UNESP] 18 December 2003 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:31:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-12-18Bitstream added on 2014-06-13T19:41:53Z : No. of bitstreams: 1 fontes_ir_dr_botfca.pdf: 6105136 bytes, checksum: 23e89a651c99005b7465ec2d3aae3e9b (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O presente trabalho teve como objetivo a configuração de um sistema de supervisão e controle de irrigação utilizando técnicas de inteligência artificial. De acordo com metodologia adotada, o seu desenvolvimento foi realizado em três fases distintas. Inicialmente foram construídos os seguintes módulos de hardware: Unidade de Sensores, Unidade Concentradora de Dados e Sensor de Umidade do Solo do tipo Capacitivo. Em seguida foi criada uma aplicação através do programa de supervisão e controle do tipo SCADA, Elipse PRO, dedicada à supervisão e controle de uma casa de vegetação. Na fase final foram coletados os dados necessários para o treinamento de uma rede neural artificial que é parte integrante do sensor de umidade de solo do tipo capacitivo. Os resultados obtidos através de um conjunto de teste de medidas demonstraram que o sensor capacitivo apresenta comportamento e desempenho similares ao do sensor de do tipo TDR, o que permite concluir que esta solução pode representar uma significativa contribuição, viabilizando a implantação de sistemas de supervisão e controle em processos de irrigação com uma relação custo/benefício em níveis aceitáveis. / The present work had as objective the configuration of a supervisory and control system for irrigation using artificial intelligence techniques. In agreement with adopted methodology, its development was accomplished in three different phases. Initially the following hardware modules were built: Sensors Unit, Data Concentrator Unit and a Capacitive type Soil Moisture Sensor. Soon afterwards an application was created through the supervisory and control program of the type SCADA, Ellipse PRO, dedicated to the supervision and control of a green house. In the final phase the necessary data were collected for the training of an artificial neural network that is integral part of the capacitive type soil moisture sensor. With the application developed in the Ellipse PRO a database was created for the training of the artificial neural network, containing a group of 2440 measures of soil moisture obtained through a capacitive type sensor and a TDR type sensor. The results obtained through a group of test of measures demonstrated that the capacitive sensor presents a similar behavior to the of the TDR type sensor, the one that allows conclude that this solution can represent a significant contribution, making possible the implantation of supervisory and control systems in irrigation processes with a cost/benefit relationship in acceptable levels.
973

Avaliação dos níveis de umidificação e aquecimento durante ventilação artificial com a estação de trabalho de anestesia Primus da Dräger com baixo fluxo de gases frescos e permutador de calor e umidade

Castro Júnior, Jair de [UNESP] 12 February 2009 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:35:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-02-12Bitstream added on 2014-06-13T20:26:17Z : No. of bitstreams: 1 castrojunior_j_dr_botfm.pdf: 761536 bytes, checksum: 8c6353cd6eec74b90409bf5498e8e3f5 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Durante anestesia geral com intubação traqueal para manutenção das vias aéreas, a umidificação e o aquecimento artificial dos gases inalados são essenciais para a prevenção de alterações na mucosa traqueobrônquica e diminuição do risco de hipotermia não intencional durante a cirurgia. A estação de trabalho de anestesia Primus (Dräger, Lübeck, Alemanha) tem placa de metal aquecida, situada na parte expiratória do circuito, para a prevenção da condensação de água no sistema respiratório. Esta placa aquecida também pode ajudar na manutenção da temperatura do gás no circuito respiratório em valores adequados. O presente estudo teve como objetivo a determinação da temperatura esofágica e da temperatura e umidade dos gases anestésicos no circuito respiratório do aparelho Primus da Dräger usando baixo fluxo de gases frescos (FGF) associado ou não ao uso do permutador de calor e umidade (PCU). Participaram do estudo trinta pacientes adultas com estado físico ASA I e II submetidas a cirurgias ginecológicas eletivas. As pacientes foram distribuídas aleatoriamente em dois grupos sob ventilação com baixo FGF de 1 L.min-1 com ou sem PCU durante anestesia geral com sistema circular respiratório com absorvedor de CO2. Todas as pacientes receberam aquecimento ativo da superfície cutânea por meio de manta térmica colocada sobre os membros inferiores. A temperatura e umidades relativa e absoluta dos Introdução e Literatura 6 gases e a temperatura esofágica foram medidas aos 15 minutos (tempo controle) após instalação do sistema de ventilação nas pacientes e, então, a cada 30 minutos até 120 minutos após o tempo controle. A temperatura e a umidade relativa e absoluta dos gases inalados no grupo com baixo FGF ao PCU apresentaram valores mais elevados comparados aos do grupo com baixo FGF sem PCU (p < 0,05). Não houve redução na temperatura... / In general anesthesia with endotracheal intubation, maintenance of airway humidity and temperature is important to prevent damage to the tracheobronchial mucosa and to risk the drop in body temperature during surgery. The anesthesia Primus’s work station (Dräger, Lübeck, Germany) has a built-in hot plate coupled to heat expired gases to prevent water condensation in the breathing system, but this heating plate also may help maintaining gas temperature in the respiratory system at adequate levels. In the present study, we measured the inspired gas temperature and humidity of the anesthetic circuit in the Dräger Primus machine using low fresh gas flow with or without a heat and moisture exchanger (HME). Thirty adult ASA I and II women patients scheduled to gynaecologic surgeries were randomly assigned into two groups to received low fresh gas flow of 1 L.min-1 with or without HME in the circle anesthesia system. All patients received active skin-surface warming with a specific blanket from a warming device. Relative humidity, absolute humidity, and temperature of inspired gases and esophageal temperature were measured at 15 min and then every 30 min up to 120 min after the installation of the respiratory system. There was a significantly higher relative humidity, absolute humidity and temperatures of the inspired gases in the HME group compared to without HME group (p < 0.05). The esophageal temperature did not decrease in Introdução e Literatura 8 the group HME (p > 0.05), but decreased significantly intraoperatively in without HME group (p < 0.05). Low-flow with the breathing system of the Dräger Primus anesthesia workstation have inherent humidifying properties sufficient to reduce the risk of respiratory tract dehydration only after 90 minutes of anaesthesia. The addition of HME improves the inspiratory absolute humidity, relative humidity and temperature of the anesthetic... (Complete abstract click electronic access below)
974

Concreto com adição de cinza de bagaço de cana-de-açúcar

Fernandes, Sérgio Eduardo [UNESP] 18 August 2014 (has links) (PDF)
Made available in DSpace on 2015-06-17T19:34:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-08-18. Added 1 bitstream(s) on 2015-06-18T12:47:01Z : No. of bitstreams: 1 000829587.pdf: 1025900 bytes, checksum: caf14058fe0da647247682c65c55da7c (MD5) / O concreto de alto desempenho (CAD) possui uma densa microestrutura que lhe proporciona ao mesmo, alta resistência e redução de sua permeabilidade. Com isso, apresenta alta durabilidade, sendo maior que a do concreto convencional. Esse fato mostra que a utilização deste concreto está crescendo rapidamente em diversas obras. Este produto tem como base a cinza de bagaço de cana-de-açúcar (CBC), que possui grande potencial para ser utilizada como aditivo mineral em concretos, uma vez que é composta por dióxido de silício. A partir dessas afirmações, esta pesquisa apresenta a finalidade de analisar o desempenho da adição de CBC sem sofrer o processo de moagem, na fabricação do concreto de alto desempenho. Para tanto, foi feita a substituição de CBC na proporção de 5%, 10%, 15% e 20%, sendo esta substituída na quantidade de agregado miúdo em massa. Os ensaios realizados foram: absorção, módulo de elasticidade, resistência à compressão e resistência à tração por compressão diametral para as idades de 7, 28, 60 e 90 dias. Chegou-se, portanto, à conclusão que o CAD com CBC de substituição em 20% de agregado miúdo em massa foi o que obteve o melhor desempenho, por isso foi o traço escolhido para os ensaios de durabilidade, tais como: resistência ao ataque químico, absorção por capilaridade, frente à penetração de cloretos, ensaio de abrasão/erosão e permeabilidade à água. Assim, os resultados obtidos nos ensaios foram comparados aos mesmos ensaios realizados com o concreto referência, ou seja, CAD sem nenhuma adição. A partir daí, observou-se que, em determinados casos, o CAD com adição de CBC apresentou resultados iguais ou até mesmo superiores ao do concreto referência / The high performance concrete (CAD) has a dense microstructure which provides the same, high strength and reduced permeability. With this, it has high durability, being greater than that of conventional concrete. This fact makes their use is growing rapidly in several works. Regarding bagasse ash cane sugar (CBC), this has great potential to be used as a mineral additive for concrete, since it is composed of silicon dioxide. Thus, this research has the purpose of analyzing the performance of the addition of CBC without undergoing milling, manufacturing of high performance concrete. Replacement of was which is substituted in the proportion of 5%, 10%, 15% and 20%, the amount of aggregate in massa. Os tests were performed: absorption, modulus of elasticity, compressive strength and tensile strength by diametrical compression to the ages of 7, 28, 60 and 90 days. Was reached, so the conclusion that CAD with CBC replacement in 20% of aggregate mass, was what had the best performance, so it was chosen for durability testing trait and which were the following: resistance to chemical attack, wicking, across the penetration of chlorides abrasion test / erosion and water permeability. The results obtained in the tests were compared to tests performed with the same reference concrete, that is, without addition CAD, showing in some cases, the addition of CAD with CBC showed equal or even superior results to the reference concrete
975

Utilização da cinza de folha de cana-de-açúcar como material pozolânico em matrizes cimentantes

Moraes, João Cláudio Bassan de [UNESP] 27 February 2015 (has links) (PDF)
Made available in DSpace on 2015-07-13T12:10:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-02-27. Added 1 bitstream(s) on 2015-07-13T12:25:22Z : No. of bitstreams: 1 000837061.pdf: 1904789 bytes, checksum: 8b4d526ca7ac778c3a7ead4be26f6682 (MD5) / O cimento Portland é largamente utilizado na construção civil, sendo também um dos materiais mais utilizados do mundo. Porém, há uma grande emissão de CO 2 na produção do cimento Portland, então surge a busca por materiais alternativos na construção civil. Outro problema está relacionado com o crescimento da produção de cana-de-açúcar no Brasil. A folha de cana-de-açúcar é um subproduto da colheita da cana-de-açúcar, e ela possui como qualidade o seu poder calorífico para geração de energia, que é comparável ao do bagaço de cana-de-açúcar. Entretanto, a produção de energia a partir da queima da folha de cana-de- açúcar gera um resíduo, a cinza de folha de cana-de-açúcar. Este resíduo é o principal elemento deste trabalho, objetivando seu uso como material pozolânico em matrizes cimentantes substituindo parcialmente o cimento Portland. Neste trabalho, é estudado desde a produção desta cinza até a sua utilização em matrizes cimentantes. Primeiramente, é estudado o modo de obtenção de uma cinza com boas qualidades pozolânicas. Portanto, são utilizados fornos para queimar a folha e obter a cinza, depois esta passa por um processo de peneiramento e, finalmente, a moagem do material. Após obter a cinza, esta é caracterizada pela Composição Química, Difração de Raio-X, Granulometria, Espectroscopia de Infravermelho por Transformada de Fourier, Análise Termogravimétrica e Microscopia Eletrônica de Varredura. Em seguida, após a caracterização de cinza, esta é aplicada em pastas de cal/pozolana e cimento/pozolana com o objetivo de analisar sua reatividade pozolânica. Ensaios de Espectroscopia de Infravermelho por Transformada de Fourier, Análise Termogravimétrica e Microscopia Eletrônica de Varredura são utilizados como análise da evolução da reação pozolânica. Finalmente, a cinza é aplicada em argamassas substituindo parcialmente em massa... / Portland cement is widely used in building construction, and one of the mostly materials used in the world. However, Portland cement production generates huge amount of CO 2, and, consequently, researches for alternative materials in building construction is growing up. Another problem is related to growth of sugarcane production in Brazil. Sugar cane straw is a byproduct of harvesting sugar cane, and one of its qualities is the calorific value for power generation that can be compared to sugar cane bagasse. However, the production of energy from burning sugar cane straw generates a waste, the sugar cane straw ash. The residue is the maing element in this work, aiming its use as pozzolanic material in cementitious binder replacing partially the Portland cement. In this work, is studied since the production of this ash until this use in cementing matrices. First, the method of obtaining a good ash with pozzolanic qualities is studied. Therefore, furnaces are used to burn the straw and obtain the ash, then it passes through sieves, and finally grinding the material. After obtaining the ash, it is characterized from Chemical Composition, X-Ray Diffraction, Particle Size, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis and Scanning Electron Microscopy. Then, after characterizing the ash, it is assessed in cement pastes/pozzolan and lime/pozzolan to evaluate their pozzolanic reactivity. Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis and Scanning Electron Microscopy are used to evaluate the development of pozzolanic reaction. Finally, the ash is used in mortars replacing partially in mass the Portland cement to evaluate the mechanical properties. Four different substitutions were assessed and were compared to the control with no sugarcane straw ash. Results from characterization of sugar cane straw ash and pastes, as well as mechanical properties of mortars, show ...
976

Análise estrutural de tubos de concreto armado com resíduo de borracha de pneu

Trentin, Thiago Francisco Silva [UNESP] January 2014 (has links) (PDF)
Made available in DSpace on 2015-08-20T17:09:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2014. Added 1 bitstream(s) on 2015-08-20T17:27:13Z : No. of bitstreams: 1 000844371.pdf: 4204307 bytes, checksum: fb22d1267c606f6fa3de44ae3a52f036 (MD5) / O concreto é um material que apresenta uma série de vantagens, como, por exemplo, boa durabilidade, baixa permeabilidade, resistência às condições atmosféricas e grande resistência frente aos esforços de compressão. Estas qualidades fizeram com que sua aplicação fosse difundida para a confecção de tubos de concreto destinados à captação e transporte de água da chuva uma vez que estes elementos são normalmente enterrados, e, deste modo, estão sujeitos a esforços de compressão e expostos à ação da água. No entanto, o concreto tem algumas limitações, como, por exemplo, baixa resistência à tração, elevado peso próprio, facilidade de fissuração e um comportamento frágil na ruptura. Assim, novos materiais passaram a ser estudados a fim de se encontrar novos componentes que pudessem minimizar as suas limitações. Um deles é o resíduo de borracha de pneu, que pode proporcionar ao concreto uma maior capacidade de deformação e também uma distribuição mais eficaz das tensões atuantes. Além disso, este resíduo também pode proporcionar um aumento da absorção de energia e uma diminuição da propagação de fissuras no estado endurecido. No entanto, vários estudos mostram que a inclusão de resíduos de borracha no concreto provoca uma diminuição da resistência mecânica à compressão, uma diminuição da trabalhabilidade das misturas e um aumento do teor de ar incorporado. Nesta pesquisa foi feita uma análise do comportamento estrutural de cinco tubos de concreto armado, sendo um deles sem adição de resíduo de borracha (traço TC), dois deles com uma quantidade de resíduos igual a 10 kg de borracha por metro cubico de concreto (traço TR 10) e outros dois com uma quantidade de resíduo de 20 kg de borracha por metro cubico de concreto (traço TR 20). Todos os tubos confeccionados tinham um diâmetro nominal de 60 cm e um comprimento efetivo de 150 cm. Para... / The concrete material has a number of advantages like durability, low permeability, weather resistance and high compressive strength. These qualities have led its application to the rainwater collection, since the pipes are usually buried, and, thus, are subjected to compressive forces and exposed to the action of water. However, the concrete has some limitations, as, for example, low resistance to tensile stress, high self-weight, ease of cracking and a brittle behavior in rupture. Thus, many materials are being studied in order to be used as a new concrete component, seeking to minimize its disadvantages. One of them is the tire rubber residue. This residue is a fibrous material that takes a long time to decompose and increases the amount of trash in landfills, but it may give a greater deformation capacity and also a more effective distribution of stresses to the concrete. Furthermore, the tire rubber residue can provide an increase in energy absorption and a decrease in the propagation of cracks in the hardened state. However several studies show that the inclusion of tire rubber residue in the concrete causes a decrease in the mechanical strength to compression, a decrease in the workability of the mixtures and an increase of the content of entrained air. This work deals with the analysis of the structural behavior of five reinforced concrete pipes: one without the addition of tire rubber residue (designated as TC); two of them with an content of residue equal to 10 kg of residue per cubic meter of concrete (designated as TR 10); and the last two with a quantity of 20 kg per cubic meter of concrete (designated as TR 20). All the pipes had a nominal diameter of 60 cm and an effective length of 150 cm. In order to quantify the strength of the pipes, the diametral compression tests were performed according to the recommendations of the NBR 8890 (ABNT, 2007). The diametral displacements at the hub ...
977

Response to population in corn hybrids with specific characteristics

Schroeder, Nathan January 1900 (has links)
Master of Agribusiness / Department of Agricultural Economics / Allen M. Featherstone / Examining the interaction between population and corn yield is important because the challenge of feeding the world is real. Projections show the world population is increasing and expected to reach over 9 billion people by around 2050. Expanding global urbanization drives the need to increase corn yield on current land and needs to occur to meet global population growth. Previous studies on corn yield increases conclude that ear size is limited and increasing corn plants per acre is important to increasing yield potential. This study used Answerplot data to analyze the effect of increasing plant population on corn yield in 2009. There are over 150 Answerplots across the cornbelt. The weather of 2009 proved to be a challenging year in certain regions of the cornbelt. Record rainfall, and below normal temperature had an influence on corn yield. A total of 4,180 observations from Answerplot were used from across the nation to analyze the relationship between corn yield and plant population. Multiple regression models were estimated and found that in 2009, an increase in plant population from 30,000 to 40,000 plants per acre resulted in an 8.5 bushel per acre increase. This result was robust for various econometric models. Economically, the cost per acre for current seed for this increase in population is about $38.87 per acre. At a corn price greater than $4.58 per bushel, increasing plant population would have made economic sense for 2009.
978

Using an Ecohydrology Model to Explore the Role of Biological Soil Crusts on Soil Hydrologic Conditions at the Canyonlands Research Station, Utah

January 2015 (has links)
abstract: Biological soil crusts (BSCs) dominate the soil surface of drylands in the western United States and possess properties thought to influence local hydrology. Little agreement exists, however, on the effects of BSCs on runoff, infiltration, and evaporative rates. This study aims to improve the predictive capability of an ecohydrology model in order to understand how BSCs affect the storage, retention, and infiltration of water into soils characteristic of the Colorado Plateau. A set of soil moisture measurements obtained at a climate manipulation experiment near Moab, Utah, are used for model development and testing. Over five years, different rainfall treatments over experimental plots resulted in the development of BSC cover with different properties that influence soil moisture differently. This study used numerical simulations to isolate the relative roles of different BSC properties on the hydrologic response at the plot-scale. On-site meteorological, soil texture and vegetation property datasets are utilized as inputs into a ecohydrology model, modified to include local processes: (1) temperature-dependent precipitation partitioning, snow accumulation and melt, (2) seasonally-variable potential evapotranspiration, (3) plant species-specific transpiration factors, and (4) a new module to account for the water balance of the BSC. Soil, BSC and vegetation parameters were determined from field measurements or through model calibration to the soil moisture observations using the Shuffled Complex Evolution algorithm. Model performance is assessed against five years of soil moisture measurements at each experimental site, representing a wide range of crust cover properties. Simulation experiments were then carried out using the calibrated ecohydrology model in which BSC parameters were varied according to the level of development of the BSC, as represented by the BSC roughness. These results indicate that BSCs act to both buffer against evaporative soil moisture losses by enhancing BSC moisture evaporation and significantly alter the rates of soil water infiltration by reducing moisture storage and increasing conductivity in the BSC. The simulation results for soil water infiltration, storage and retention across a wide range of meteorological events help explain the conflicting hydrologic outcomes present in the literature on BSCs. In addition, identifying how BSCs mediate infiltration and evaporation processes has implications for dryland ecosystem function in the western United States. / Dissertation/Thesis / Masters Thesis Geological Sciences 2015
979

Investigation of Subgrade Moisture Flow Caused by Hydro-Thermal Gradients In Airfield Pavements

January 2017 (has links)
abstract: Recent research efforts have been directed to improve the quality of pavement design procedures by considering the transient nature of soil properties due to environmental and aging effects on pavement performance. The main purpose of this research study was to investigate the existence of subgrade soil moisture changes that may have arisen due to thermal and hydraulic gradients at the Atlantic City NAPTF and to evaluate their effect on the material stiffness and the California Bearing Ratio (CBR) strength parameter of the clay subgrade materials. Laboratory data showed that at the same water content, matric suction decreases with increasing temperature; and at the same suction, hydraulic conductivity increases with increasing temperature. Models developed, together with moisture/temperature data collected from 30 sensors installed in the test facility, yielded a maximum variation of suction in field of 155 psi and changes in hydraulic conductivity from 2.9E-9 m/s at 100% saturation to 8.1E-12 at 93% saturation. The maximum variation in temperature was found to be 20.8oC at the shallower depth and decreased with depth; while a maximum variation in moisture content was found to be 3.7% for Dupont clay and 4.4% for County clay. Models developed that predicts CBR as a function of dry density and moisture content yielded a maximum variation of CBR of 2.4 for Dupont clay and 2.9 for County clay. Additionally, models were developed relating the temperature with the bulk stress and octahedral stress applied on the subgrade for dual gear, dual tandem and triple tandem gear types for different tire loads. It was found that as the temperature increases the stresses increase. A Modified Cary and Zapata model was used for predicting the resilient modulus(Mr) of the subgrade. Using the models developed and the temperature/moisture changes observed in the field, the variation of suction, bulk and octahedral stresses were estimated, along with the resilient modulus for three different gear types. Results indicated that changes in Mr as large as 9 ksi occur in the soils studied due to the combined effect of external loads and environmental condition changes. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2017
980

Performance Evaluation of Reclaimed Asphalt Pavement in Hot Mix Asphalt Modified with Organosilane

January 2018 (has links)
abstract: Use of Recycled Asphalt Pavement (RAP) in newly designed asphalt mixtures is becoming a common practice. Depending on the percentage of RAP, the stiffness of the hot mix asphalt (HMA) increases by incorporating RAP in mixes. In a climatic area such as the City of Phoenix, RAP properties are expected to be more oxidized and aged compared to other regions across the US. Therefore, there are concerns about the cracking behavior and long-term performance of asphalt mixes with high percentage of RAP. The use of Organosilane (OS) in this study was hypothesized to reduce the additional cracking potential and improve resistance to moisture damage of the asphalt mixtures when using RAP. OS has also the potential to improve the bond between the aggregate and asphalt binder. The use of OS also reduces the mixing and compaction temperatures required for asphalt mixtures, making it similar to a warm mix asphalt (WMA), Six asphalt mixes were prepared with three RAP contents, 0%, 15% and 25%, with and without Organosilane. The mixing temperature was reduced by 10°C and the compaction temperature was reduced by 30°C. Mix designs were performed, and the volumetric properties were compared. The mixture laboratory performance was evaluated for all mixtures by conducting Dynamic Modulus, Flow Number and Tensile Strength Ratio tests. The study findings showed that mixtures achieved better compaction at a reduced temperature of 30°C. Mixtures modified with Organosilane generally exhibited softer behavior at the extreme ends of lower and higher temperatures. The lower moduli are to reduce the potential for cracking. For the Flow Number test, the RAP mixtures with OS passed the minimum required at all traffic levels. Tensile Strength Ratio results increased with the increase in RAP percentage, and further increase was observed when OS was used. The OS reduced the sticking nature of the binder to the molds and equipment, which reduced the efforts in cleaning them. Finally, the future use of RAP by the City of Phoenix would positively contributes to their sustainability aspiration and initiatives. The use of Organosilane may even facilitates higher percentage of RAP usage; it definitely improves the moisture resistance of asphalt mixtures, especially when lower mixing and compaction temperatures are desired or used. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2018

Page generated in 0.0193 seconds