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Search Results: 1 - 10 of 719177 matches for " A. L. de;Liborio "
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Desempenho de concretos avan?ados para a constru??o civil, formulados a partir do método de dosagem computacional
Castro, A. L. de;Liborio, J. B. L.;Pandolfelli, V. C.;
Ceramica , 2009, DOI: 10.1590/S0366-69132009000300002
Abstract: the search for materials with better mechanical performance and durability has been the aim of the concrete's technology researchers. in order to attain this target, concretes developed with engineering microstructure are necessary. based on the concepts of particle packing and dispersion, it is possible to obtain materials with dense matrix and appropriate workability. thus, in the present paper, the properties of concretes based on these concepts are presented and compared to those high performance ones used in building site researches. the fresh properties were evaluated measuring the fluidity index and the rheological behavior of the material. in the hardened condition, the mechanical strength were evaluated by the compressive, splitting tensile and 3 point bending tests, whereas the young's modulus were measured by the static and dynamic methods. the new concretes showed to be more workable for a longer period of time than the reference one, without the need of retarding admixtures addition. in terms of mechanical strength, it was possible to verify higher reproducibility for the concretes designed with the computing mix proportion technique. besides that, it was also possible to establish good correlations between the strength measured for these concretes, as well for the young's modulus measured by both test methods.
A influência do tipo de cimento no desempenho de concretos avan?ados formulados a partir do método de dosagem computacional
Castro, A. L. de;Liborio, J. B. L.;Pandolfelli, V. C.;
Ceramica , 2011, DOI: 10.1590/S0366-69132011000100002
Abstract: when a concrete is produced, especially a high performance one, the first concern is the cement type to be used, making this binder an essential compound. the rheological properties of high performance concretes are related to the hydration of cement aluminates phase, whereas the development of mechanical strength depends on the hydrated silicates formed. thus, variations on cement characteristics influence the properties of a concrete, being observed different behaviors for mixtures produced with distinct cements. the present paper aims to evaluate the influence of cement type on the performance of special concretes designed using computing techniques. the fresh properties were evaluated measuring the fluidity index and the rheological behavior of the material. in the hardened condition, the mechanical strength were evaluated by the compressive, splitting tensile and 3 point bending tests, whereas the young's modulus was measured by the static and dynamic methods. by comparing all the measured properties, the concretes produced with portland cement showed better performance than that containing calcium aluminate cement, being the high early strength portland cement more efficient than the slag-modified portland cement for the production of high performance mixtures and until the age of 28 days.
Reologia de concretos de alto desempenho aplicados na constru??o civil: revis?o
Castro, A. L. de;Liborio, J. B. L.;Pandolfelli, V. C.;
Ceramica , 2011, DOI: 10.1590/S0366-69132011000100009
Abstract: from a rheological point of view, concrete can be understood as a concentrate suspension of solid particles (aggregates) in a viscous liquid (cement paste). in such case, its fresh behavior should be evaluated based on the concepts of rheology, the science which relates the deformation and flow of a fluid under stress influence. several studies had already been accomplished along the time, resulting in a series of equations that describe the fresh concrete behavior. it is known that the rheological behavior of this material is close to that of a bingham fluid and two rheological parameters are required for its description: yield stress and plastic viscosity. the rheology of fresh concrete has been studied by measurements that vary among simple and practical test methods, such as the slump test, and more sophisticated equipments that determine the flow curve of the material, such as the rheometer. therefore, it is possible to attain a correlation between shear stress and shear rate under conditions defined physically. as fresh concrete is a heterogeneous material, a more accurate approach of its rheological behavior is given by the direct analysis of the forces (torque) that result from the shear (rotation speed) of the concrete. thus, this paper presents a review concerning the main concepts related with the rheology of high performance concretes applied in building site, which involves the rheological characterization and the test methods used for the measurement of the rheological properties.
Rice hull-derived silica: applications in Portland cement and mullite whiskers
Souza M.F. de,Batista P.S.,Regiani I.,Liborio J.B.L.
Materials Research , 2000,
Abstract: Silica was extracted from rice hulls by three processing routes, starting with acid treatment followed by burning and milling. The amorphous white silica powder showed a surface area of 260 to 480 m2/g, purity above 99% and average particle size of 2.0 to 0.6 mm. This silica is suitable for the preparation of mullite whiskers employing the rare earth aluminosilicate glass technique. Due to its highly pozzolanic reaction, this prepared silica is used as an additive in high performance concrete.
Rice hull-derived silica: applications in Portland cement and mullite whiskers
Souza, M.F. de;Batista, P.S.;Regiani, I.;Liborio, J.B.L.;Souza, D.P.F. de;
Materials Research , 2000, DOI: 10.1590/S1516-14392000000200005
Abstract: silica was extracted from rice hulls by three processing routes, starting with acid treatment followed by burning and milling. the amorphous white silica powder showed a surface area of 260 to 480 m2/g, purity above 99% and average particle size of 2.0 to 0.6 mm. this silica is suitable for the preparation of mullite whiskers employing the rare earth aluminosilicate glass technique. due to its highly pozzolanic reaction, this prepared silica is used as an additive in high performance concrete.
Initial rheological description of high performance concretes
Castro, Alessandra Lorenzetti de;Liborio, Jefferson Benedicto Libardi;
Materials Research , 2006, DOI: 10.1590/S1516-14392006000400011
Abstract: concrete is defined as a composite material and, in rheological terms, it can be understood as a concentrated suspension of solid particles (aggregates) in a viscous liquid (cement paste). on a macroscopic scale, concrete flows as a liquid. it is known that the rheological behavior of the concrete is close to that of a bingham fluid and two rheological parameters regarding its description are needed: yield stress and plastic viscosity. the aim of this paper is to present the initial rheological description of high performance concretes using the modified slump test. according to the results, an increase of yield stress was observed over time, while a slight variation in plastic viscosity was noticed. the incorporation of silica fume showed changes in the rheological properties of fresh concrete. the behavior of these materials also varied with the mixing procedure employed in their production. the addition of superplasticizer meant that there was a large reduction in the mixture's yield stress, while plastic viscosity remained practically constant.
Response of castor bean to arbuscular mycorrhizal fungi and levels of phosphorus Resposta da mamoneira a fungos micorrízicos arbusculares e a níveis de fósforo
Oswaldo Machineski,Elcio Liborio Balota,José Roberto Pinto de Souza
Semina : Ciências Agrárias , 2011,
Abstract: The aim of this study was to evaluate the response of castor bean inoculated with arbuscular mycorrhizal fungi (AMF) and different levels of P in the soil. The experiment was carried out under greenhouse condition, in Londrina-PR, using disinfected sandy soil (LVd) as substrate, in pots with capacity of 4 kg. The treatments were conducted in a randomized factorial design, using Iris castor bean cultivar. The treatments with mycorrhizal were: Control, Gigaspora margarita, Glomus clarum, and a mixture of species, and five levels of P (0, 20, 40, 80, 160 mg P kg soil-1), with four replicates. There were evaluated: dry mass, content of P in the shoot and mycorrhization. There was a significant effect of arbuscular mycorrhizal fungi inoculation on the dry mass and in the P content in the shoot. The addition of P influenced, significantly, the production of dry mass and P content in the plant tissue, however it decreases the root colonization and mycorrhizal sporulation. The castor bean show dependence of AMF in soil with low levels of P. O objetivo no presente estudo foi avaliar a resposta da mamoneira inoculada com fungos micorrízicos arbusculares (FMA) e diferentes níveis de P no solo. O experimento foi conduzido em casa de vegeta o, em Londrina-PR, com a utiliza o de solo arenoso (LVd) autoclavado como substrato, em vasos com capacidade de 4 kg. Os tratamentos foram instalados em um esquema fatorial A x B, casualizados, sendo utilizado o híbrido de mamona Iris. Fator A: representado pela inocula o dos fungos micorrízicos: Controle, Gigaspora margarita, Glomus clarum, e uma mistura de espécies, e o fator B pelos cinco níveis de P (0, 20, 40, 80, 160 mg P kg solo-1), com quatro repeti es. Foram avaliados: massa seca de plantas, micorriza o e o teor de P na parte aérea. Houve efeito significativo da inocula o de fungos micorrizícos arbusculares na massa seca e no teor de P na parte área. A adi o de doses de P influenciou de modo significativo a produ o de matéria seca e os teores de P no tecido, porém diminuiu a coloniza o radicular e o número de esporos de FMA. A mamoneira mostrou-se dependente de FMA no solo com baixo nível de P.
Improvement of physical and chemical properties of concrete with brazilian silica rice husk (SRH)
Silva,Fernanda Giannotti da; Liborio,Jefferson B. L.; Helene,Paulo;
Revista ingeniería de construcción , 2008, DOI: 10.4067/S0718-50732008000100002
Abstract: the use of industrial and agricultural waste substitutions for portland cement has greatly contributed to sustainable development practices. the increase in cement demand will be met by the use of supplementary cementing materials, in order to minimize the clinker consumption. in this study, the effects of silica extracted from rice husk (srh) as a partial replacement of cement in concretes with low water/binder are reported. the properties investigated include compressive strength, splitting tensile strength, water absorption by immersion, water absorption by capillarity and resistance to chloride ion penetration. the research indicates that srh is an effective mineral addition for designing durable concrete presenting an optimal performance when the replacement ratio of portland cement is around 10%
Improvement of physical and chemical properties of concrete with brazilian silica rice husk (SRH) La mejora de propiedades físicas y químicas de hormigón con silice de cáscara de arroz (SRH) brasile a
Fernanda Giannotti da Silva,Jefferson B. L. Liborio,Paulo Helene
Revista ingeniería de construcción , 2008,
Abstract: The use of industrial and agricultural waste substitutions for Portland cement has greatly contributed to sustainable development practices. The increase in cement demand will be met by the use of supplementary cementing materials, in order to minimize the clinker consumption. In this study, the effects of silica extracted from rice husk (SRH) as a partial replacement of cement in concretes with low water/binder are reported. The properties investigated include compressive strength, splitting tensile strength, water absorption by immersion, water absorption by capillarity and resistance to chloride ion penetration. The research indicates that SRH is an effective mineral addition for designing durable concrete presenting an optimal performance when the replacement ratio of Portland cement is around 10% El uso de desechos industriales y agrícolas como segmento en la producción de cemento Portland ha contribuido de manera importante en la práctica de desarrollo sustentable. El aumento en la demanda de cemento coincide con el uso de materiales aglomerantes suplementarios para minimizar el consumo de clinker. En este estudio, se informan los efectos de la sustitución parcial de cemento Portland por sílice extraído de la cascara de arroz (SRH) en hormigones con baja relación agua/materiales cementicios. Las propiedades investigadas incluyen resistencia a la compresión, resistencia a la tracción, absorción de agua por inmersión, absorción de agua por capilaridad y resistencia a la penetración de iones de cloruro. La investigación indica que SRH es una adición mineral eficaz para el dise o de hormigones durables que presenta una actuación óptima cuando la proporción del reemplazo de cemento de Portland está alrededor de 10%
Analytical/numerical solution for confined jet diffusion flame (sandia flame c)
De Bortoli,A. L.;
Latin American applied research , 2009,
Abstract: the aim of the present work is the development of a method based on the momentum transfer law to obtain the solution of confined jet diffusion flames. the reichardt's equation is used to approximate the flow/mixture fraction and it is discretized based on the second order finite difference technique. all thermochemical variables are determined by the mixture fraction as the sandia flame c, used to check the results, is close to equilibrium. the semi-analytical/numerical results compare reasonably with the experimental data indicating that the method contributes to solve some jet flames at low cost.
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