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‣ On the classification of mixed construction and demolition waste aggregate by porosity and its impact on the mechanical performance of concrete

Angulo, Sérgio Cirelli; Carrijo, Priscila Meireles; Figueiredo, Antonio Domingues de; Chaves, Arthur Pinto; John, Vanderley Moacyr
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
Português
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The properties of recycled aggregate produced from mixed (masonry and concrete) construction and demolition (C&D) waste are highly variable, and this restricts the use of such aggregate in structural concrete production. The development of classification techniques capable of reducing this variability is instrumental for quality control purposes and the production of high quality C&D aggregate. This paper investigates how the classification of C&D mixed coarse aggregate according to porosity influences the mechanical performance of concrete. Concretes using a variety of C&D aggregate porosity classes and different water/cement ratios were produced and the mechanical properties measured. For concretes produced with constant volume fractions of water, cement, natural sand and coarse aggregate from recycled mixed C&D waste, the compressive strength and Young modulus are direct exponential functions of the aggregate porosity. Sink and float technique is a simple laboratory density separation tool that facilitates the separation of cement particles with lower porosity, a difficult task when done only by visual sorting. For this experiment, separation using a 2.2 kg/dmA(3) suspension produced recycled aggregate (porosity less than 17%) which yielded good performance in concrete production. Industrial gravity separators may lead to the production of high quality recycled aggregate from mixed C&D waste for structural concrete applications.; FINEP (Fundo Verde e Amarelo/Habitare); SINDUSCON-SP; FAPESP; CNPq; CAPES

‣ Contribuições ao estudo da influência de propriedades de agregados no comportamento de misturas asfálticas densas; Contributions to the study of effects of aggregate properties on mechanical behavior of hot mix asphalt (HMA)

Gouveia, Lilian Taís de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 04/12/2006 Português
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O objetivo principal desta pesquisa é avaliar a influência que as propriedades estudadas dos agregados exercem sobre propriedades volumétricas e mecânicas de misturas asfálticas densas. Para tanto, foram avaliadas as propriedades de consenso e de origem, especificadas pelo Superpave, de um conjunto de agregados, além de suas densidades, porosidade, absorção e adesividade. Foram estudados agregados de gabro, basalto e areia natural e três tipos de granulometrias, uma denominada AZR, passando acima da zona de restrição da especificação Superpave, e outras duas, obtidas através do sistema de seleção granulométrica Bailey. Também três níveis de energia de compactação foram aplicados às misturas, 75, 110 e 155 golpes por face do corpo-de-prova Marshall. Avaliou-se o comportamento mecânico das misturas através dos ensaios de estabilidade e fluência Marshall, fluência por compressão uniaxial uniforme, fluência por compressão uniaxial dinâmica, resistência à tração, módulo de resiliência e fadiga. Os resultados mostraram que, de uma maneira geral, o agregado de gabro apresentou superioridade em relação ao agregado de basalto e de areia natural, tanto quando analisado isoladamente como quando analisado nas misturas asfálticas. Suas características de forma...

‣ Comportamento mecânico de agregado reciclado de resíduo sólido da construção civil em camadas de base e sub-base de pavimentos.; Mechanical behavior of recycled aggregate of construction and demolition waste in base and sub base layers of pavements.

Leite, Fabiana da Conceição
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/06/2007 Português
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Os resíduos de construção e demolição (RCD) são gerados em quantidades expressivas nas cidades de grande e médio portes no Brasil e são comumente descartados de forma irregular. Para os milhares de quilômetros de vias urbanas não pavimentadas, o agregado reciclado de resíduo sólido da construção civil é uma alternativa aos materiais convencionais de pavimentação. Esta dissertação analisa o comportamento mecânico do agregado reciclado para emprego em camadas de base e sub-base. A pesquisa consiste em ensaios laboratoriais, acompanhados de um estudo de caso - o pavimento do novo campus da Universidade de São Paulo (USP Leste). Um trecho de 1.020 metros de extensão foi utilizado no estudo, de um total de aproximadamente dois quilômetros de vias pavimentadas no campus. O pavimento avaliado possui agregado reciclado em sua estrutura; quatro seções-tipo diferentes foram construídas, variando os materiais, as espessuras, a compactação e o subleito. Propriedades físicas e mecânicas do agregado reciclado foram determinadas em laboratório por meio dos seguintes testes: composição, porcentagem de materiais indesejáveis, massa específica, absorção de água, graduação, forma dos grãos, compactação, influência da compactação...

‣ Estudo do comportamento mecânico de um agregado reciclado de concreto para utilização na construção rodoviária; Study of the mechanical behavior of a recycled concrete aggregate for use in the road construction

Grubba, David Christian Regis Pereira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/09/2009 Português
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Os resíduos de construção e demolição (RCD) representam cerca da metade dos resíduos sólidos urbanos. No Brasil, sua geração anual corresponde a aproximadamente 68 milhões de toneladas. Uma forma de se mitigar os impactos ambientais oriundos da disposição desses resíduos sobre o meio ambiente é o seu beneficiamento na forma de agregados reciclados. Os agregados reciclados podem ser classificados em dois grupos, agregados reciclados mistos e agregados reciclados de concreto (ARC). Entre as diversas formas de aplicação dos agregados reciclados, destaca-se a construção rodoviária por utilizar quantidade expressiva tanto de materiais graúdos, quanto de miúdos. No Brasil, ainda existem poucos relatos científicos sobre o desempenho de agregados reciclados de concreto em camadas de pavimentos. Assim, o objetivo desta pesquisa é estudar as propriedades físicas e o comportamento mecânico, através da análise de resultados de ensaios laboratoriais, do agregado reciclado de concreto proveniente da Usina de Reciclagem de Resíduos da Construção Civil de São Carlos-SP, visando seu emprego em camadas de base e sub-base de pavimentos. Foram realizados ensaios de caracterização física, lixiviação, solubilização...

‣ The Private Memory of Aggregate Shocks

Costa, Carlos Eugênio da; Luz, Vitor F.
Fonte: Escola de Pós-Graduação em Economia da FGV Publicador: Escola de Pós-Graduação em Economia da FGV
Tipo: Relatório
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We study constrained efficient aggregate risk sharing and its consequence for the behavior of macro-aggregates in a dynamic Mirrlees’s (1971) setting. Privately observed idiosyncratic productivity shocks are assumed to be independent of i.i.d. publicly observed aggregate shocks. Yet, private allocations display memory with respect to past aggregate shocks, when idosyncratic shocks are also i.i.d.. Under a mild restriction on the nature of optimal allocations the result extends to more persistent idiosyncratic shocks, for all but the limit at which idiosyncratic risk disappears, and the model collapses to a pure heterogeneity repeated Mirrlees economy identical to Werning [2007]. When preferences are iso-elastic we show that an allocation is memoryless only if it displays a strong form of separability with respect to aggregate shocks. Separability characterizes the pure heterogeneity limit as well as the general case with log preferences. With less than full persistence and risk aversion different from unity both memory and non-separability characterize optimal allocations. Exploiting the fact that non-separability is associated with state-varying labor wedges, we apply a business cycle accounting procedure (e.g. Chari et al. [2007]) to the aggregate data generated by the model. We show that...

‣ Desempenho de concretos com agregados reciclados de cerâmica vermelha; Performance of red ceramic recycled aggregate concrete

Cabral, Antonio Eduardo Bezerra; Schalch, Valdir; Dal Molin, Denise Carpena Coitinho; Ribeiro, Jose Luis Duarte; Ravindrarajah, Rasiah Sri
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
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Os resíduos de construção e demolição (RCD) constituem uma importante parcela dos resíduos sólidos produzidos nas cidades brasileiras, correspondendo em torno de 50% dos resíduos sólidos urbanos. Dentre os diversos constituintes do RCD, a cerâmica vermelha, proveniente de restos de tijolos e telhas cerâmicas utilizados nas construções, equivale a uma considerável parcela destes resíduos. A reciclagem do RCD para a produção de agregados reciclados tem se tornado uma prática cada vez mais comum, particularmente em cidades onde há uma inacessibilidade ou escassez de agregados naturais, proporcionando altos custos para adquiri-los. Com o intuito de se determinar o comportamento do agregado reciclado de cerâmica vermelha na produção de concretos, desenvolveu-se um programa experimental baseado em um projeto de experimentos onde se substituiu os agregados miúdos e graúdos naturais pelos seus respectivos reciclados, além de se variar a relação água/cimento. Os concretos produzidos foram analisados com relação a três propriedades: resistência à compressão, módulo de deformação e volume de poros permeáveis (VPP). Os resultados obtidos foram analisados utilizando-se ferramentas estatísticas, desenvolvendo-se modelos matemáticos que descrevem o comportamento das propriedades estudadas ao se substituir o agregado natural pelos reciclados de cerâmica vermelha. Todos os modelos obtiveram excelentes coeficientes de determinação...

‣ Influência do grau de cristalinidade e deformação do quartzo no desencadeamento da reação álcali-agregado; Influence of the crystallinity and deformation of quartz on alkali-aggregate reaction

Bonsembiante, Francieli Tiecher
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Tese de Doutorado Formato: application/pdf
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Este estudo se propôs a avaliar a influência da cristalinidade e da deformação do quartzo na ocorrência da reação álcali-agregado. A influência da cristalinidade do quartzo foi analisada através da mesóstase, material intersticial que constitui as rochas vulcânicas, que é um material composto por grãos sub-microscópicos de quartzo e feldspatos. Para tanto foram selecionadas duas rochas vulcânicas, constituídas por quartzo em diferentes quantidades e com diferentes graus de cristalinidade: um basalto, com pouca quantidade de sílica, sem quartzo livre e cuja mesóstase apresenta grãos pobremente cristalizados; e um riolito, com grande quantidade de sílica e de quartzo livre, além de uma mesóstase com grãos melhor cristalizados. A caracterização da cristalinidade do quartzo mostrou que a mesóstase, que tem aparência de material amorfo em microscopia ótica, apresenta diferentes feições quando observada através de microscopia eletrônica de varredura: mesóstase com grãos criptocristalinos de quartzo e K-feldspatos (Mm); mesóstase com grãos de quartzo e feldspato microcristalinos (Mq); mesóstase constituída predominantemente por argilominerais (Ma). Relacionando-se essas características com a reatividade das rochas verificou-se que o quartzo presente nas mesóstases Mm e Mq reage rápida e intensamente...

‣ Development of a laboratory test for characterization of asphalt-aggregate adhesion

Pais, Jorge C.; Silva, Hugo Manuel Ribeiro Dias da; Pereira, Paulo A. A.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /04/2002 Português
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The mechanical properties of bituminous mixtures depend on the adhesion between mastic and aggregate, as well as on the cohesion within the mastic. These properties vary as a function of the composition of the bituminous mixture, of the chemical and physical features of the aggregate and bitumen and of the condition under which the mixing is carried out. It is thus fundamental to develop an adhesion test, which is of easy execution and, at the same time, represents correctly the bituminous mixture and its mechanical behaviour, essentially the aggregate-mastic adhesion. The test described here simulates the behaviour of a small representative specimen of the bituminous material subject to increasing tension or shear force, inducing rupture of the aggregate-mastic bond. The specimens have a prismatic shape and comprise a single large piece of aggregate between two layers of mastic. The efficiency of the aggregate-mastic bond will be evaluated by the necessary force to rupture the specimen and by the form of rupture. The results obtained from this test will not only allow the features which most influence the adhesion of mastic to aggregate to be established, but also reveal the best aggregate-fines-binder combinations as a function of the type of aggregate and bituminous mixture.

‣ Dynamic compressive behavior of recycled aggregate concrete based on split Hopkinson pressure bar tests

Lu,Yubin; Chen,Xing; Teng,Xiao; Zhang,Shu
Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 Português
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This paper presents the experimental results of recycled aggregate concrete (RAC) specimens prepared with five different amount of recycled coarse aggregate (RCA) [i.e. 0, 25%, 50%, 75% and 100%] subjected to compressive loading based on split Hopkinson pressure bar tests. Strain-rate effects on dynamic compressive strength and critical strain of recycled aggregate concrete were studied. Results show that impact properties of recycled aggregate concrete exhibit strong strain-rate dependency, and increase approximately linearly with strain-rate. The transition point from low strain-rate sensitivity to high sensitivity decreases with the increase of matrix strength.

‣ Influência dos Agregados Graúdos da Região de Goiânia no Módulo de Deformação Tangente Inicial do Concreto; Influence of coarse aggregate in the region of Goiânia Initial Tangent Modulus of Deformation of Concrete

BARBOSA, Isa Lorena Silva
Fonte: Universidade Federal de Goiás; BR; UFG; Mestrado em Engenharia Civil; Engenharias Publicador: Universidade Federal de Goiás; BR; UFG; Mestrado em Engenharia Civil; Engenharias
Tipo: Dissertação Formato: application/pdf
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This research is carried out to study the influence of aggregate source on the initial tangent modulus of deformation of concrete (Eci), to correlate the resistance to compression (fc) with the module Eci and compare the results of this research with the equations proposed by international standards and the Brazilian. To this end, it was used three levels of resistance to 28 days: 20MPa, 30Mpa and 40Mpa and ranged up the aggregate source in the types lithological micaschist, Granulito and Basalt. Set the type of cement, sand, water, and additive content of mortar. All materials are used in dosages of Goiânia and the surrounding region in order to determine the behavior of these materials in concrete that is produced in the region. The experimental program of this research is divided into two parts. The first is to determine the curves of strength of each aggregate source test of resistance to compression in the age of three, seven and 28 days, while the second part determines the initial tangent modulus of deformation on the ages of seven and 28 days. For the first part of the experimental program were molded 54 body-of-evidence and tested for resistance to compression. For the second part was molded 90 body-of-evidence, where 36 were tested for resistance to compression and 54 with the initial tangent modulus of deformation. With the end of testing was performed a statistical analysis of results obtained through software STATISTIC. In the analysis it was the influence of aggregate source in the initial tangent modulus of deformation (Eci)...

‣ Governance Matters VIII : Aggregate and Individual Governance Indicators 1996–2008

Kaufmann, Daniel; Kraay, Aart; Mastruzzi, Massimo
Fonte: Banco Mundial Publicador: Banco Mundial
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This paper reports on the 2009 update of the Worldwide Governance Indicators (WGI) research project, covering 212 countries and territories and measuring six dimensions of governance between 1996 and 2008: Voice and Accountability, Political Stability and Absence of Violence/Terrorism, Government Effectiveness, Regulatory Quality, Rule of Law, and Control of Corruption. These aggregate indicators are based on hundreds of specific and disaggregated individual variables measuring various dimensions of governance, taken from 35 data sources provided by 33 different organizations. The data reflect the views on governance of public sector, private sector and NGO experts, as well as thousands of citizen and firm survey respondents worldwide. The authors also explicitly report the margins of error accompanying each country estimate. These reflect the inherent difficulties in measuring governance using any kind of data. They find that even after taking margins of error into account, the WGI permit meaningful cross-country comparisons as well as monitoring progress over time. The aggregate indicators...

‣ Governance Matters VII : Aggregate and Individual Governance Indicators 1996-2007

Kaufmann, Daniel; Kraay, Aart; Mastruzzi, Massimo
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
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This paper reports on the latest update of the Worldwide Governance Indicators (WGI) research project, covering 212 countries and territories and measuring six dimensions of governance between 1996 and 2007: Voice and Accountability, Political Stability and Absence of Violence/Terrorism, Government Effectiveness, Regulatory Quality, Rule of Law, and Control of Corruption. The latest aggregate indicators are based on hundreds of specific and disaggregated individual variables measuring various dimensions of governance, taken from 35 data sources provided by 32 different organizations. The data reflect the views on governance of public sector, private sector and NGO experts, as well as thousands of citizen and firm survey respondents worldwide. The authors also explicitly report the margins of error accompanying each country estimate. These reflect the inherent difficulties in measuring governance using any kind of data. The authors also briefly describe the evolution of the WGI since its inception, and show that the margins of error on the aggregate governance indicators have declined over the years...

‣ Governance Matters V : Aggregate and Individual Governance Indicators for 1996–2005

Kaufmann, Daniel; Kraay, Aart; Mastruzzi, Massimo
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
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The authors report on the latest version of the worldwide governance indicators, covering 213 countries and territories and measuring six dimensions of governance from 1996 until end-2005: voice and accountability, political stability and absence of violence, government effectiveness, regulatory quality, rule of law, and control of corruption. The latest indicators are based on hundreds of variables and reflect the views of thousands of citizen and firm survey respondents and experts worldwide. Although global averages of governance display no marked trends during 1996-2005, nearly one-third of countries exhibit significant changes [for better or for worse] on at least one dimension of governance. Three new features distinguish this update. (1) The authors have moved to annual reporting of governance estimates. This update includes new governance estimates for 2003 and 2005, as well as minor backward revisions to biannual historical data for 1996-2004. (2) The authors are, for the first time, publishing the individual measures of governance from virtually every data source underlying the aggregate governance indicators. The ready availability of the individual data sources underlying the aggregate governance indicators is aimed at further enhancing the transparency of the methodology and of the resulting aggregate indicators...

‣ The usefulness of aggregate indicators in policy making and evaluation: a discussion with application to eco-efficiency indicators in New Zealand

Jollands, Nigel
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Working/Technical Paper Formato: 252426 bytes; 353 bytes; application/pdf; application/octet-stream
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Aggregate indices can assist decision-making by summarising a complex array of information. However, little research has been conducted on aggregate environmental indicators. The purpose of this paper is to address the debate surrounding aggregate environmental indices. In doing so, the paper highlights the strengths and weaknesses of aggregate indices for use in decision-making. We conclude that aggregate indices do have a role in assisting decision makers, as long as they are not used in isolation from more detailed information. The paper addresses several methodological issues that must be addressed when calculating aggregate indicators including selection of appropriate aggregation functions, weighting, and selecting variables for inclusion in the aggregation function. The methodological issues are applied to a case study of New Zealand data. Specifically, we apply principal components analysis (PCA) to eco-efficiency indicators. This case study reveals that PCA is an effective approach to aggregating eco-efficiency indicators. In doing so, we have identified an aggregation technique that is appropriate for increasing-scale indicators and can assist decision makers by reducing redundancy in the indicators matrix, while providing results that are consistent with the more detailed information.; no

‣ Aggregate coalescence and factors affecting it.

Hasanah, Uswah
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2007 Português
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The phenomenon called soil aggregate coalescence occurs at contact-points between aggregates and causes soil strength to increase to values that can inhibit plant root exploration and thus potential yield. During natural wetting and drying, soil aggregates appear to ‘weld’ together with little or no increase in dry bulk density. The precise reasons for this phenomenon are not understood, but it has been found to occur even in soils comprised entirely of water stable aggregates. Soil aggregate coalescence has not been widely observed and reported in soil science and yet may pose a significant risk for crops preventing them from achieving their genetic and environmental yield potentials. This project used soil penetrometer resistance and an indirect tensile-strength test to measure the early stages of aggregate coalescence and to evaluate their effects on the early growth of tomato plants. The early stages of aggregate coalescence were thought to be affected by a number of factors including: the matric suction of water during application and subsequent drainage, the overburden pressure on moist soil in the root zone, the initial size of soil aggregates prior to wetting, and the degree of sodicity of the soil aggregates. Seven mainexperiments were conducted to evaluate these factors. The matric suction during wetting of a seedbed affects the degree of aggregate slaking that occurs...

‣ Lightweight Aggregate Potentialities of Some Indiana Shales

Murray, Haydn H.; Smith, John M.
Fonte: Indiana Geological Survey Publicador: Indiana Geological Survey
Tipo: Relatório Formato: 16655371 bytes; application/pdf
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Indiana Geological Survey Report of Progress 12; Laboratory tests show that some Indiana shales are potential sources of manufactured lightweight aggregate. Bloating, the process by which lightweight aggregates are manufactured, is caused by various constituents acting singly or in combination. Chemical composition and mineral composition of the shales and particle-size distribution of the mineral constituents are interrelated, and all of these factors contribute to the bloating of shales. This study was made to test the potential use of some Indiana, shales as raw materials for manufacturing lightweight aggregate. Such aggregate was produced in Ohio, Illinois, and Kentucky before any interest was shown in Indiana. A new plant is now producing lightweight aggregate from shale of the Borden group near Brooklyn, Ind., but other plants are needed to meet the increasing demand for lightweight concrete in the State. It is hoped that this report will stimulate interest in developing lightweight aggregate from shale and will enable future producers of lightweight aggregate in Indiana to evaluate better the location, thickness, extent, and physical properties of various shale formations.; Indiana Department of Conservation

‣ EVALUATION OF THE ENVIRONMENTAL, MATERIAL, AND STRUCTURAL PERFORMANCE OF RECYCLED AGGREGATE CONCRETE

Michaud, Katherine
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
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Concrete is the most commonly used building material in the construction industry, and contributes to 52% of construction and demolition waste in Canada. Recycled concrete aggregate (RCA) is one way to reduce this impact. To evaluate the performance of coarse and granular (fine and coarse) RCA in structural concrete applications, four studies were performed: an environmental assessment, a material testing program, a shear performance study, and a flexural performance study. To determine the environmental benefits of recycled aggregate concrete (RAC), three case studies were investigated using different populations and proximities to city centres. Environmental modelling suggested that RCA replacement could result in energy savings and greenhouse gas emission reductions, especially in remote areas. Tests were performed to determine if the volumetric replacement of up to 30% coarse RCA and 20% granular RCA is suitable for structural concrete applications in Canada. Fresh, hardened, and durability properties were evaluated. All five (5) of the RCA mixes showed equivalent material performance to the control mixes and met the requirements for a structural concrete mix. The five (5) RAC mixes were also used in structural testing. One-way reinforced concrete slab specimens were tested to failure to evaluate the shear and flexural performance of the RAC members. Peak capacities of and crack formation within each member were analyzed to evaluate the performance of RAC compared to conventional concrete. The shear capacity of specimens made from four (4) of the five (5) RAC mixtures was higher or equivalent to the control specimens. Specimens of the concrete mixture containing the highest content of recycled aggregate...

‣ Effect of solid loading and aggregate size on the rheological behavior of PDMS/Calcium Carbonate suspensions

Behzadfar,E.; Abdolrasouli,M. H.; Sharif,F.; Nazockdast,H.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2009 Português
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The purpose of this study is to examine the effect of solid loading and aggregate size on the rheological behavior of PDMS (polydimethylsiloxane)/CC (calcium carbonate) suspensions. Mixtures containing 10 to 40 vol% of CC were prepared; the effect of shear rate and particle content on aggregate size and rheological properties was studied. Rheological properties including viscosity, loss modulus, storage modulus and yield stress were measured using rotational and oscillatory rheometry. Casson's equation was found to satisfactorily model the samples' stress response as a function of shear rate for different solid content. While solid content did not have any effect on the aggregate size, shear rate did influence the aggregate median diameter. It was observed that suspensions with higher aggregate size had a higher viscosity. In general, for a given volume fraction, a small change in the aggregate size had a significant impact on the viscosity, particularly at low shear rates.

‣ Aggregate designated verifier signatures and application to secure routing

Bhaskar, Raghav; Herranz, Javier; Laguillaumie, Fabien
Fonte: Inderscience Publishers Publicador: Inderscience Publishers
Tipo: Artículo Formato: 180053 bytes; application/pdf
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10 pages.; A designated verifier signature convinces only the specific recipient of the message of its integrity and origin. Following the notion of aggregate signature introduced by Boneh et al. we introduce in this work the notion of aggregate designated verifier signature. After defining the protocols and the security model for such schemes, we give a general construction which is based on message authentication codes and that can be extended to an identity-based scenario. The resulting schemes are proved to be secure under the Computational Diffie–Hellman (CDH) assumption, in the random oracle model. They are much more efficient than standard aggregate signature schemes, at the price of losing some properties of standard signatures, in particular non-repudiation. Finally we explain the possible application of aggregate designated verifier signatures to the authentication of messages in routing protocols. We compare our new scheme with existing standard aggregate signature schemes and show why our solution with aggregate designated verifier signatures is more suitable for securing routing in mobile ad hoc networks.; Peer reviewed

‣ Laser-based assessment of road aggregate particle shape and texture properties with the aim of deriving comparative models

Breytenbach,J; Anochie-Boateng,J K; Paige-Green,P; van Rooy,J L
Fonte: Journal of the South African Institution of Civil Engineering Publicador: Journal of the South African Institution of Civil Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 Português
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Research was undertaken using an innovative three-dimensional (3D) laser scanning tool to study the shape and texture characteristics of road aggregate particles. Aggregate materials used for road construction, including G1 crushed rocks of different geological origins, recycled aggregate and alluvial gravel (not used as aggregate) were used for this study. Representative samples were scanned using the laser system to collect 3D aggregate data for analyses and, subsequently, develop comparative models. The objective was to arrange the aggregate particles in a sequence based on their surface texture. Two models were proposed and key aspects evaluated against each other. Ultimately, one model was selected that may be improved and used for further research. The study found that, while it is possible to use the 3D aggregate scan data to produce comparative models, distinguishing between particle shape and texture proved a daunting task. It was also concluded that particle elongation must be considered as a major influencing factor.