• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 300
  • 289
  • 59
  • 55
  • 23
  • 13
  • 13
  • 8
  • 5
  • 3
  • 3
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 936
  • 278
  • 271
  • 197
  • 134
  • 128
  • 128
  • 121
  • 102
  • 98
  • 95
  • 88
  • 76
  • 68
  • 66
  • 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.
801

Electrical properties of road materials and subgrade soils and the use of Ground Penetrating Radar in traffic infrastructure surveys

Saarenketo, T. (Timo) 01 November 2006 (has links)
Abstract This PhD thesis is composed of a synopsis and five published papers that are focused on both the research results of studies on electrical properties of road materials and subgrade soils and their seasonal changes and the use of Ground Penetrating Radar technique in traffic infrastructure surveys. The data for this survey was collected mainly in Finland, Texas, Scotland and Sweden and thus presents many kinds of road materials, subgrade soils and climate conditions. The synopsis of this work begins with a presentation of the theory and basic principles of GPR techniques. Special attention is given to the dielectric properties and seasonal changes of unbound road materials and subgrade soils. The synopsis also presents different kinds of GPR hardware systems as well as recommendations and experiences from different data collection, processing and interpretation techniques. Special attention is given to a method whereby GPR data is integrated with other road survey data and then analysed using a number of structural diagnostic methods. Finally, the synopsis provides an overview of of the various GPR applications on roads and streets, bridges, railways and airports. The laboratory test results presented in this work show that the relationship between dielectric value and increasing water content is not linear or exponential but more likely a series of logarithmic functions. Laboratory results also showed that dielectric dispersion, which can be related to poorly performing subgrade soils and road aggregates, takes place mainly in loosely bound adsorption water and capillary water layer. As such these moisture sensitive problem materials can also be identified during the dry summer seasons when they are stiff. Dielectric value and electrical conductivity can also be related to other technical properties of road materials and subgrade soils such as frost susceptibility, shear strength, plastic limit, compaction degree and voids content. Laboratory tests and field data collected using the Percostation technique also demonstrate that a knowledge of seasonal changes and thermodynamics is very important in understanding and modelling the mechanical behaviour of road structures. Finally, laboratory and field tests indicate that colloids have an important role in the failure mechanism of the road materials. This research demonstrates that the GPR technique not only gives valuable structural information on the different types of structures and subgrade soils but it provides a wide range of information of the electrical properties of the materials under survey which can be further related to their mechanical performance. The best information will be gained if GPR data is analysed together with other non destructive testing data collected form the roads, railways and airports.
802

Etude physico-chimique des possibilités de valorisation des sables argileux non conformes dans des mélanges bitumineux routiers / A mineralogical approach to use the non-qualified fine aggregates in asphalt concrete pavement

Chen, Chi-Wei 29 March 2016 (has links)
Ma thèse de doctorat doit contribuer à la diminution du gaspillage des ressources naturelles (en particuliers les sables naturels) en étendant leur acceptabilité dans les enrobés bitumineux. La compréhension de l’effet des particules nocives, notamment la fraction argileuse contenue dans les sables, sur le comportement des mélanges bitumineux est visé. Pour évaluer le niveau de nocivité des particules fines, le test d'adsorption du bleu de méthylène noté MB (EN13043, NF EN 933-9) est appliqué, mais un tel test a été modifié à quatre reprises au cours des 22 dernières années tandis que la valeur de bleu limite, utilisée pour déterminer la conformité ou non du sable, n’a pas été modifiée. Le projet de thèse vise à modifier cette valeur limite pour étendre la gamme de sable utilisable. Cet objectif sera atteint grâce à l’identification de la composition minéralogique des sables, une recherche sur la meilleure manière de quantifier les phases qui composent les sables et une meilleure compréhension du rôle de la fraction fine sur la durabilité et les pathologies des mélanges bitumineux. Le travail de thèse est organisé en différentes tâches : 1. Tester le protocole de mesure de la valeur de bleu. Nous voulons comprendre l'effet de différents facteurs (tels que l'échantillonnage, la cinétique des additions de bleu, la température de séchage du sable avant l’essai ...) sur la mesure de la valeur de bleu. Le développement d'un appareil automatique ou d'une nouvelle méthode (qui sera validée par comparaison avec les résultats obtenus à partir de la méthode standardisée) est prévu.2. Établir une corrélation entre la valeur de bleu (ou d'autres paramètres à trouver) et la quantité de phases minérales présentes dans les sables. Un jeu de données a d’ores et déjà été établi au cours de mon stage de master. Pour atteindre cet objectif, les différentes méthodes de quantification (utilisant en particuliers la diffraction de rayons X) doivent être testées et comparées.3. Corréler la valeur de bleu couplée à la nature minéralogique des particules fines avec le comportement mécanique des mélanges sable/bitume. Nous allons étudier la dégradation en présence d’eau des propriétés du matériau bitumineux (par exemple l'adhésion du liant bitumineux sur granulat) et le rôle de la couche de particules fines qui entourent les grains de sable sur les propriétés mécaniques de ce matériau. Nous espérons comprendre en particulier l'effet de la présence d’argile gonflante dans les matériaux constitutifs de la chaussée bitumineuse.4. Améliorer le comportement des granulats non conformes par l’application d’un traitement. Après l'identification de l'origine des pathologies (nous faisons l'hypothèse que les argiles gonflantes jouent un rôle majeur), nous proposons d'appliquer un traitement en ajoutant de la chaux (ou de traiter en ajoutant des déchets qui contiendraient des substances actives comme la chaux), et de tester également l’utilisation de polymères ou du greffage avec des composés organiques des argiles comme traitement / Siliceous fines (clays) in fine aggregates used for AC pavement stimulate the moisture entering the bitumen-aggregates interface in AC mixture and create channels for water penetration. MB adsorption for qualifying fine aggregates is in accordance with the layer charge and the accessibility of consisted mineralogy in fine aggregates. However, the correlation between MB qualification for fine aggregates and fine aggregates triggering moisture susceptibility of AC mixture has not ever been addressed; moreover, the questions from MB adsorption still remain to be solved. In order to evaluate the stripping and to clarify MB adsorption on fine aggregates from a mineralogical perspective, the most common clays in natural aggregates, kaolinite, illite and montmorillonite, were extracted from their clay rocks, and used to prepare thin clay film, artificial fine aggregates and asphalt concrete mixtures consist of artificial fine aggregates. Moreover, the 5 blinded fine aggregates received from quarries without any given information were applied as the blinded experiments to confirm the practicability with mineralogical diversity. The mineralogical analysis was identifying and quantifying the mineral phases in extracted clay and fine aggregates by using X-Ray diffraction, and the quantitative results were judged by complementary test. MB adsorption was studied using drop method, UV-Photometer method and cation exchange capacity from clays and aggregates. Water-bitumen-clay interaction was studied using the sessile drop and the Oliensis spot tests on those thin clay films. The water intrusion routes in AC mixture was investigated immersing AC mixture in solution with chemical probe, whereas Duriez tests allowed measuring the moisture susceptibility of AC mixtures containing varied clay mineralogy in fine aggregates. The results show that clay mineralogy is in relation to water-bitumen-clay interaction, and it is agreed by moisture susceptibility of AC mixture indicated by Duriez test. With the dispersive nature bitumen used in this study, cohesive failure is in the light of kaolinite-AC mixture in the presence of water, whereas swelling property is responsible for the stripping in illite- and montmorillonite- AC mixture. In order to exclude the physical interferences on MB adsorption, the vale of 100% of MB adsorption on fine aggregates referred to CEC value is necessary to apply, and MB value measured from drop method efficiently excludes the significant impacts from layer charge, pH value and exchangeable cations. Although MB adsorption is in relation to clay mineralogy, this test does not sufficiently indicate the stripping of AC mixture occurred by clay in fine aggregates. There are still rooms to use the non-qualified fine aggregates for the use of AC pavement. As Rietveld method from X-Ray diffraction derives the most reasonable quantitative results, the X-Ray powder diffraction and the X-Ray orientated EG treated K-saturated clay diffraction are proposed for analyzing clay mineralogy and its swelling property for judging the use of non-qualified fine aggregates for AC mixture.MB2 and Duriez0.8 surfaces can be established on clay mineralogical map since we discovered MB adsorption and moisture susceptibility are related to clay mineralogy in fine aggregates. The fine aggregates which is not qualified by MB adsorption is going to confirm the possibility for the use of AC pavement by the mineralogical analysis through X-Ray diffraction. By adopting the quantitative results of clay on mineralogical map with Duriez0.8 surface and the swelling property of clays in fine aggregates, the use of fine aggregates for AC pavement can be properly judged according to water-bitumen-aggregates interaction and stripping which has been proved in this study
803

Innovative Modular High Performance Lightweight Decks for Accelerated Bridge Construction

Ghasemi, Sahar 13 November 2015 (has links)
At an average age of 42 years, 10% of the nation’s over 607,000 bridges are posted for load restrictions, with an additional 15% considered structurally deficient or functionally obsolete. While there are major concerns with decks in 75% of structurally deficient bridges, often weight and geometry of the deck further limit the load rating and functionality of the bridge. Traditional deck systems and construction methods usually lead to prolonged periods of traffic delays, limiting options for transportation agencies to replace or widen a bridge, especially in urban areas. The purpose of this study was to develop a new generation of ultra-lightweight super shallow solid deck systems to replace open grid steel decks on movable bridges and as well serve as a viable alternative in bridge deck replacements across the country. The study has led to a lightweight low-profile asymmetric waffle deck made with advanced materials. The asymmetry comes from the arrangement of primary and secondary ribs, respectively perpendicular and parallel to the direction of traffic. The waffle deck is made with ultrahigh performance concrete (UHPC) reinforced with either high-strength steel (HSS) or carbon fiber reinforced polymer (CFRP) reinforcement. With this combination, the deck weight was limited to below 21 psf and its overall depth to only 4 inch, while still meeting the strength and ductility demands for 4 ft. typical stringer spacing. It was further envisioned that the ultra-high strength of UHPC is best matched with the high strength of HSS or CFRP reinforcement for an efficient system and the ductile behavior of UHPC can help mask the linear elastic response of CFRP reinforcement and result in an overall ductile system. The issues of consideration from the design and constructability perspectives have included strength and stiffness, bond and development length for the reinforcement, punching shear and panel action. A series of experiments were conducted to help address these issues. Additionally full-size panels were made for testing under heavy vehicle simulator (HVS) at the accelerated pavement testing (APT) facility in Gainesville. Detailed finite element analyses were also carried out to help guide the design of this new generation of bridge decks. The research has confirmed the superior performance of the new deck system and its feasibility.
804

Estudo das características hidráulicas e mecânicas de calçadas em concreto permeável em pista experimental. / Study of the mechanical and hydraulic characteristics of experimental pervious concrete sidewalks.

Batezini, Rafael 30 May 2019 (has links)
A presente pesquisa teve como objetivo principal a realização de estudos laboratoriais, de campo e numéricos, buscando viabilizar duas misturas de concreto permeável que foram utilizadas na construção de duas calçadas experimentais localizadas no campus da USP em São Paulo. Nas pistas experimentais foi realizado o acompanhamento da capacidade permeável ao longo do tempo, além da avaliação das suas respostas estruturais frente à aplicação de carregamentos dinâmicos por meio de equipamento FWD, considerando a variação do teor de umidade no interior das estruturas. Por fim, foram realizadas retroanálises com uso de diferentes softwares procurando entender qual das camadas da estrutura apresenta maior vulnerabilidade estrutural frente à presença de volumes excessivos de água. Os resultados da etapa laboratorial indicaram que há uma sensibilidade muito grande no comportamento das misturas em função do teor de aditivo superplastificante, uma vez que houve segregação severa da pasta de cimento no fundo dos corpos de prova quando esse teor ultrapassou determinado limite. Os resultados dos ensaios de taxa de infiltração em campo possibilitaram a proposição um modelo empírico para estimativa do desempenho da capacidade hidráulica para calçadas em concreto permeável executadas na região de São Paulo. Os resultados dos levantamentos deflectométricos e das retroanálises indicaram variação considerável na capacidade de suporte do conjunto base+subleito entre as calçadas, além de evidenciar considerável perda da capacidade de suporte dessas estruturas quanto submetidas à presença de elevados volumes de água no seu interior. Palavras chave: concreto permeável, calçada, pavimento, taxa de infiltração, levantamento deflectométrico, análise estrutural, retroanálise. / The main goal of this research was to carry out laboratorial, field and numerical studies with the purpose of defining two feasible pervious concrete mixtures to be used as the surface layer of two experimental sidewalks in the campus of the University of São Paulo. The permeability capacity of the sidewalks was monitored along time, as well as its structural responses in terms of deflections due to application of FWD dynamic loadings, assessing how the structural behavior was impacted by the presence of high volumes of water into the permeable structure. A backcalculation procedure was used in order to assess the elastic behavior of the structure layers, as well as find out which layer of the structure is the most vulnerable in terms of mechanical behavior under the presence of excessive volumes of water. The results in the laboratory indicates that pervious concrete mixtures are considerable sensitives to the amount of superplasticizer additive, since a severe mortar segregation was observed on the bottom of the specimens casted using some of the mixtures produced. The results of infiltration tests in field made it possible to develop an empirical model capable of estimating the hydraulic performance of pervious concrete permeable sidewalks in São Paulo region. The results of the deflection measurements and the backcalculations indicated a considerable variation on the bearing capacity of the infrastructure (base+subgrade) between the two sidewalks. In addition, it is evident the loss of bearing capacity of the structure under the presence of excessive amount of water into the sidewalk.
805

Estudio comparativo del efecto en el confort térmico de los pavimentos asfálticos y de concreto con diatomita en microclimas con ENVI-met / Comparative study of the effect in thermal comfort of asphalt and concrete with diatomite pavements with ENVI-met

Basurto Villafuerte, Jean Paul Luis, Chirinos Hurtado, Carlos Arturo 14 December 2020 (has links)
El presente artículo evalúa de manera comparativa el confort térmico en el uso de los pavimentos asfalticos frente a los pavimentos de concreto con adición de diatomita. La variable que se considerará para el estudio será la reflectancia. Para la comparación se utilizará el software ENVI-met donde se modelará zonas de Lima identificadas como Islas de Calor (UHI) que usen pavimentos asfalticos las cuales, en el modelo, serán reemplazadas por pavimentos de concreto con adición de diatomita y se obtendrá el confort térmico de todos los modelos por el método PET a través del programa ya mencionado. Finalmente se comparará dichos resultados. / This article comparatively evaluates the thermal comfort in the use of asphalt pavements versus concrete pavements with the addition of diatomite. The variable that will be considered for the study will be reflectance. For the comparison, the ENVI-met software will be used where areas of Lima that use asphalt pavements identified as Heat Islands (UHI) will be used, which will be replaced by concrete pavements with diatomite and thermal comfort will be seen by the PET method through of the aforementioned program. Finally, those results will be compared. / Trabajo de investigación
806

Water Vapor Movement in Freezing Aggregate Base Materials

Rogers, Maile Anne 18 December 2013 (has links)
The objectives of this research were to 1) measure the extent to which water vapor movement results in water accumulation in freezing base materials; 2) evaluate the effect of soil stabilization on water vapor movement in freezing base materials; 3) determine if the corresponding changes in water content are sufficient to cause frost heave during winter; 4) determine if the corresponding changes in water content are sufficient to cause reductions in stiffness during spring; 5) evaluate relationships between selected material properties, freezing conditions, and the occurrence and impact of water vapor movement; and 6) numerically simulate heat and water movement in selected pavement design scenarios. The research involved extensive laboratory and field testing, statistical analyses, and numerical modeling. The results of the laboratory testing, which included gradations, Atterberg limits, soil classifications, specific gravity and absorption values, electrical conductivity values, moisture-density relationships, soil-water characteristic curves, moisture-stiffness curves, hydraulic conductivity values, and frost susceptibility assessments, were used to characterize each material and enable subsequent statistical analyses. Testing of both treated and untreated materials enabled investigation of a wide variety of material properties. The results of the field testing, which included temperature, moisture content, water potential, elevation, and stiffness data over time, provided the basis for comparing pavement sections with and without capillary barriers and established the framework for numerical modeling. In a pavement section with a capillary barrier underlying the base layer, water vapor movement from the subgrade through the capillary barrier may be expected to increase the water content of the base layer by 1 to 3 percent during a typical winter season in northern Utah for base materials similar to those studied in this research. During winter, cold temperatures create an ideal environment for water vapor to travel upward from the warm subgrade soil below the frost line, through the capillary barrier, and into the base material. Soil stabilization can lead to increased or decreased amounts of water vapor movement in freezing base materials depending on the properties of the stabilized soil, which may be affected by gradation, mineralogy, and stabilizer type and concentration. Accumulation of water from long-term water vapor movement into frost-susceptible base materials underlain by a capillary barrier can lead to frost heave of the base layer as it approaches saturation, as water available in the layer can be redistributed upwards to create ice lenses upon freezing. However, the incremental increase in total water content that may occur exclusively from water vapor movement during a single winter season in northern Utah would not be expected to cause measurable increases in thaw weakening of the base layer during spring. Because water in a base layer overlying a capillary barrier cannot drain until nearly reaching positive pore pressures, the base layer will remain indefinitely saturated or nearly saturated as demonstrated in this research. For materials similar to those studied in this research, potentially important material properties related to the occurrence of water vapor movement during freezing include dry density, percent of material finer than the No. 200 sieve, percent of material finer than 0.02 mm, apparent specific gravity, absorption, initial water content, porosity, degree of saturation, hydraulic conductivity, and electrical conductivity. The rate at which water vapor movement occurs is also dependent on the thermal gradient within the given material, where higher thermal gradients are associated with higher amounts of water vapor movement. The numerical modeling supported the field observations that the capillary barrier effectively trapped moisture in the overlying base material, causing it to remain saturated or nearly saturated throughout the monitoring period. Only non-frost-susceptible aggregate base materials should be specified for use in cold climates in conjunction with capillary barriers, and the base material in this case should be assumed to remain in a saturated or nearly saturated condition during the entire service life of the pavement. Further study is recommended on water vapor movement in freezing aggregate base materials.
807

Nové trendy při údržbě vozovek / New trends in pavement maintenance

Březina, Ilja January 2013 (has links)
The diploma thesis is dealing with the topic of new trends in asphalt road routine maintenance with a focus on new possibilities to repair damaged road surface, especially potholes and cracks. In the diploma thesis, a new advice which uses microwave heating in resurfacing asphalt roads was developed with the aim to observe its effectiveness and the optimal repair time. The obtained results were consulted with the producer of the equipment in order to utilize this new technology for repairing potholes and cracks on asphalt road surface in standard practice.
808

Problematika zvyšování podílu R - materiálu v asfaltových směsích / The issue of increasing the proportion of reclaimed asphalt in asphalt mixtures

Urbanec, Luboš January 2013 (has links)
The subject of this Ing. thesis is asphalt mixture with increasing RAP (Reclaimed Asphalt Pavement). The theoretical part defines the terms of recycling and RAP and types of recycling. The practical part is devoted to the production and testing of asphalt mixtures with different volume RAP. The proposed asphalt mixture is asphalt concrete for base layer ACP22 +. Content of RAP in mixtures is 0%, 30%, 50% and 70%. As a special additive to soften the asphalt from RAP is used ingredient STORFLUX. For each mixture are established modulus stiffness of asphalt mixture and determined fatigue characteristics of asphalt mixture. The identified properties are compared for the different representation of RAP.
809

Řešení bezpečnostního rizika na křižovatce silnic II/379 a II/373 v obci Jedovnice / II/379 and II/373 crossroad security risk solution in the Jedovnice village

Merčáková, Petra January 2014 (has links)
This thesis investigates the design documentation of the proposal to amend the existing confusing intersection of contact on the contact rectifying junction with traffic or roundabout. The proposal is designed communications for pedestrians and bus stops. Vehicular traffic will be channeled through the protective, dividing island.
810

Novostavba bytového domu / The flat new building

Vaněček, František January 2014 (has links)
The proposed apartment building including a fixed level pavement, parking spaces and a driveway is situated on land number 723/213 and 723/184 (farm land) which is located in the southeastern part of the town Horní Stropnice along the main road towards Trhove Sviny. The apartment block has been designed as a four storey building for small and larger families in 14 seperate apartments (4 apartments each on the first, second and third floors and 2 apartments, hair salon and office on the ground floor) without any basement. The key construction feature is a wall system based on basic bands of simple concrete with a concrete mounted ceiling and a roof truss with gable roof tiles at an angle of 35°. There will be 14 apartments in total (14x 3+kitchen unit). The apartment windows will have sufficient sunlight and silencing. The main entrance, covered with a concrete porch roof, will be west facing. Each apartment will be constructed around the entrance foyer, which connects the main living quarters consisting of a combined kitchen dining room, living room , toilet, bathroom, (including bath, sink, washing machine), bedroom and one or two children's room, (depending on the size of the apartment). Ground floor terraces and 1st to 3rd floor balconies will be accesed via the living rooms. There will be a technical room on the ground floor which will have two gas boilers, a hot water cylinder, central heating distribution, sewer and some individual storage space for each apartment. The space under the staircase will serve as storage for prams or bicycles. The hair salon and building office will be built in the entrance foyer, which will include a public convenience for visitors and an entrance to the visitor's waiting room, guest rooms, individual work rooms all of which will be ready for use. A new asphalt road will enable access to the new apartment block and the neighbouring apartment block on land number 723/13.

Page generated in 0.4523 seconds