Página 1 dos resultados de 119 itens digitais encontrados em 0.017 segundos

Aderência de revestimentos externos de argamassa em substratos de concreto : influência das condições de temperatura e ventilação na cura do chapisco; External mortar rendering bond in concrete substrates : influence of temperature and ventilation conditions during the slurry layer curing

Moura, Cristiane Borges
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
603.49316%
A prevenção de manifestações patológicas em revestimentos de argamassa, em especial os descolamentos, é refletida no interesse das empresas construtoras e pesquisadores por um maior conhecimento das propriedades dos elementos constituintes do sistema, bem como dos fatores externos. Destes pode-se citar as variáveis que intervêm nos mecanismos de aderência, porém que não são controláveis, como a temperatura, umidade e ventilação. Neste contexto, o presente trabalho objetiva analisar a influência da ação do vento e da temperatura elevada durante a cura da argamassa de chapisco na aderência dos revestimentos externos de argamassa aplicados em substratos de concreto. Foram moldados prismas nas dimensões 40x45x10cm, com resistência aos 28 dias de 37MPa. Utilizou-se 3 argamassas de chapisco, uma dosada em obra com traço 1:5,67 (em massa com areia seca) e outras duas industrializadas de diferentes fabricantes. Também foram utilizadas 3 argamassas de revestimento, uma dosada em obra com traço 1:0,78:6,5 (em massa com areia seca), e outras duas industrializadas de diferentes fabricantes, sendo os mesmos das argamassas de chapisco. Combinou-se os tipos de argamassa de chapisco e revestimento juntamente com o modo de preparo de cada para a composição de diferentes sistemas de revestimento...

Avaliação das propriedades fisicas e mecanicas de concretos produzidos com os cimentos Portland de alta resistencia inicial e de alto-forno aditivados com silica ativa curados termicamente; Evaluation of physical and mechanical properties of steam cured concrete made with high early strenght Portland cement and blastfurnace slag cement containing silica fume

Paulo Sergio Bardella
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/01/2005 PT
Relevância na Pesquisa
693.4403%
A durabilidade das estruturas de concreto depende da estrutura porosa e da impermeabilidade do concreto, uma vez que a entrada de água e de agentes deletérios iniciam os processos patológicos que diminuem a vida útil de uma estrutura de concreto. Dessa forma, o objetivo deste trabalho foi avaliar a resistência mecânica, permeabilidade, absorção e carbonatação natural de concretos submetidos a diferentes condições de cura. Os procedimentos de cura adotados são normalmente utilizadds em canteiros de obra e na produção de estruturas pré-moldadas de concreto: cura imersa até a idade de 7 dias, cura ambiente e cura térmica. A cura térmica foi realizada na temperatura de 60°C. Foram empregados concretos produzidos com cimento Portland de Alta Resistência Inicial (CP V ARI) e cimento Portland de Alto Forno (CP III) sem e com sílica ativa (em substituição ao cimento na proporção de 10% em massa) para cada um dos diferentes tipos de cura utilizados. Os resultados evidenciaram que o tipo de cura afeta o desempenho do concreto. A mudança do tipo de cura aplicada proporcionou variações nas propriedades mecânicas e na durabilidade dos concretos, principalmente no que diz respeito à sua estrutura porosa. Assim, um regime de cura adequado é essencial para garantir a resistência mecânica e a durabilidade dos concretos. A utilização de sílica ativa em substituição ao cimento melhorou o desempenho dos concretos...

Estudo experimental do efeito do fogo em pilares mistos de aço e concreto; Experimental study about the fire effect in short composite column of steel and concrete

Ciro Jose Ribeiro Villela Araujo
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/02/2008 PT
Relevância na Pesquisa
510.46527%
A utilização de pilares mistos de aço e concreto é de grande importância na área estrutural, pois permite o trabalho destes elementos, proporcionando maior capacidade resistente e maior tempo de exposição ao fogo, em relação aos mesmos materiais analisados separadamente. Este trabalho proporcionará informações técnicas para o entendimento do comportamento dos pilares mistos curtos, compostos por tubos de aço preenchidos com concreto, submetidos ao efeito de altas temperaturas, da qual é avaliada a perda da capacidade resistente, levando em consideração o efeito do fogo, e a não consideração desse efeito. Apresenta-se um estudo experimental que consistiu na exposição dos pilares mistos à altas temperaturas, com e sem aplicação de carregamento durante a fase de aquecimento, no intuito de analisar a capacidade resistente residual após exposição à curvas de elevação de temperatura semelhantes a curva de incêndio padrão da norma ISO 834:1994. Também foi analisado o comportamento da temperatura na superfície externa do tubo de aço, na interface entre o aço e o concreto e a temperatura no núcleo do concreto. Desta maneira pôde-se verificar que não houve perda da capacidade resistente dos pilares mistos após serem expostos aos tempos requeridos de resistência ao fogo de 30 minutos e 60 minutos; The use of circular hollow steel filled with concrete as columns are of great importance in the structural area...

Investigation of the strength and toughness of FRHPC after exposure to high temperature

Yining, Ding; Jalali, Said; Niederegger, Christoph
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2008 ENG
Relevância na Pesquisa
599.31773%
The investigations on different fibre influences on the compressive strength, the flexural strength and ductility as well as failure pattern of fiber reinforced high-performance concrete (FRHPC) after exposure to various high temperature were carried out. The results indicated that the compressive strength of HPC without fibres declined strongly after high temperature at 900oC, the residual compressive strength was only 10% compared to the original strength. However, both steel fiber (SF) and polypropylene (PP) fiber can reduce the negative effect of high temperature on the strength. The micro PP fiber can mitigate the surface spalling of HPC member significantly, but did not show clear effect on the flexural toughness of concrete matrix. In contrary, the HPC reinforced with macro steel fiber illustrated higher flexural toughness and ultimate load bearing capacity before and after high exposure temperatures. The mechanical properties of HPC reinforced with fibre cocktail (SF + PP) were better than that of HPC reinforced with mono-fibre. Besides, the failure mode of FRHPC beams changed from pull-out of steel fibers at lower temperature to tensile failure of steel fibers at higher temperature (900 oC).; Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BPD/22680/2005; National Natural Science Foundation of China - Bolsa 50278013

Effect of temperature on systems for the reinforcement of concrete

Aguiar, J. L. Barroso de; Camões, Aires; Pimenta, T. J.; Vaz, Nelson; Araújo, Marcelo Marinho de
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Parte de Livro
Publicado em //2007 ENG
Relevância na Pesquisa
569.09668%
This paper presents an experimental work using prismatic specimens of hydraulic mortar reinforced on the exterior with steel or CFRP plates. The adhesive used was an epoxy. Two series of tests were made. In the first one, the specimens were exposed seven days to temperatures between 20 ºC and 250 ºC, after which they were subjected to flexure tests made at 20 ºC. In the second series, the specimens were exposed 24 hours to temperatures between 20 ºC and 60 ºC. The exposure to different temperatures was maintained during the flexure tests. In the first series, the efficiency of the reinforcements decreases significantly above 50 ºC. In the second series, the significant decrease of the flexure resistance occurred above 40 ºC. The simultaneous action of temperature and load leads to a lower thermal resistance than the separate action.

Effect of temperature on RC elements strengthened with CFRP

Aguiar, J. L. Barroso de; Camões, Aires; Vaz, Nelson
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Artigo de Revista Científica
Publicado em //2008 ENG
Relevância na Pesquisa
679.5468%
The strengthening of RC elements with CFRP is a technique that has been acquiring more and more potential. The bond between the CFRP reinforcement and the concrete support is usually made with epoxy adhesives. However, it is here that the integrity of the system can be affected, namely by exposure to high temperatures. In order to study the effect of an increase of air temperature on the behaviour of the epoxy adhesive, CFRP strengthened RC and reference RC specimens were tested. After cyclical thermal exposures, with temperatures rising between 20ºC and 80ºC, specimens were subjected either to compressive shear tests or bending tests. The results demonstrated that epoxy adhesive exhibits poor behaviour when subjected to increased temperatures, causing important bond deterioration. The improvement achieved with the CFRP reinforcement tends to disappear with an increase of the environment temperature. So, the thermal resistance of this strengthened system can not be considered very high. However, the inclusion of insulating materials can be a good solution to protect the strengthened RC elements. Among tested materials, the foamed polyurethane showed the best behaviour.

Adhesion between high-strength concrete, epoxy resin and CFRP

Aguiar, J. L. Barroso de; Krzywon, Rafal; Camões, Aires; Gorski, M.; Dawczynski, Szymon
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2008 ENG
Relevância na Pesquisa
596.074%
This paper presents a study on the adhesion between high-strength concrete, epoxy resin and CFRP. The adhesion of the high-strength concrete was compared with the same property measured in conventional concrete. Shear tests were made to test adhesion from concretes to epoxy resin. Flexural tests were used to evaluate the adhesion between concretes, epoxy and CFRP. The effect of temperature was also evaluated. For ordinary temperatures (20 ºC) the results showed a better flexural performance of the CFRP reinforced high-strength concrete. However, the adhesion between concrete and epoxy resin was clearly affected with the increase of temperature.

Study on residual behaviour and flexural toughness of fibre cocktail reinforced self compacting high performance concrete after exposure to high temperature

Ding, Yining; Azevedo, Cecília Maria; Aguiar, J. L. Barroso de; Jalali, Said
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2012 ENG
Relevância na Pesquisa
601.9688%
This paper analyzed the effect of different fibres on the residual compressive strength, the ultimate load and flexural toughness, the failure pattern and the fracture energy of self compacting high-performance concrete (SCHPC) after exposure to various high temperature. The micro polypropylene fiber (PP fiber) could mitigate the spalling of SCHPC member significantly, but did not show clear effect on the mechanic properties of concrete. The macro steel fiber (SF) reinforced SCHPC showed higher flexural toughness and ultimate load before and after high temperatures. The mechanical properties of hybrid fibre reinforced SCHPC (HFSCHPC) after heating were better than that of mono-fibre reinforced SCHPC. The failure mode changed from pull-out of steel fibers at lower temperature to broken down of steel fibers at higher temperature. The use of hybrid fibre can be effective in providing the residual strength and failure pattern and in improving the toughness and fracture energy of SCHPC after high temperature.; Fundação para a Ciência e a Tecnologia (FCT)

Effect of temperature on systems for the reinforcement of concrete

Aguiar, J. L. Barroso de; Camões, Aires; Pimenta, T. J.; Vaz, Nelson; Araújo, Marcelo Marinho de
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Artigo de Revista Científica
Publicado em //2007 ENG
Relevância na Pesquisa
569.09668%
This paper presents an experimental work using prismatic specimens of hydraulic mortar reinforced on the exterior with steel or CFRP plates. The adhesive used was an epoxy. Two series of tests were made. In the first one, the specimens were exposed seven days to temperatures between 20 ºC and 250 ºC, after which they were subjected to flexure tests made at 20 ºC. In the second series, the specimens were exposed 24 hours to temperatures between 20 ºC and 60 ºC. The exposure to different temperatures was mantained during the flexure tests. In the first series, the efficiency of the reinforcements decreases significantly above 50 ºC. In the second series, the significant decrease of the flexure resistance occurred above 40 ºC. The simultaneous action of temperature and local leads to a lower thermal resistance than the separate action.

Estudo do efeito da temperatura no ruído pneu-pavimento e nos parâmetros acústicos das camadas superficiais; Study the effect of temperature on tire-pavement noise and acoustic parameters of surface layers

Costa, Joana Maciel Ferreira da
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Trabalho de Conclusão de Curso
Publicado em //2014 POR
Relevância na Pesquisa
696.4306%
Dissertação de mestrado integrado em Engenharia Civil; O ruído do tráfego rodoviário é um dos principais contribuintes para o ruído ambiental, levantando várias questões pois, se por um lado, está associado a vários problemas de saúde e bem-estar, por outro a sua falta constitui um risco para a segurança dos utilizadores da estrada. Assim, torna-se imprescindível o estudo e a avaliação acústica dos pavimentos rodoviários, visto que as suas características superficiais atuam de forma ativa nos mecanismos de geração do ruído pneu-pavimento. A temperatura do ar é um dos fatores que influência o ruído rodoviário. Os seus efeitos determinam, não só o modo de propagação das ondas sonoras, como também a própria emissão dessas ondas. O trabalho desenvolvido nesta dissertação tem por objetivo estudar o efeito da temperatura no ruído da interação do pneu com o pavimento e nos parâmetros acústicos das camadas superficiais, com o recurso a vários métodos de ensaio. Para a aquisição do ruído pneu-pavimento utilizou-se o método de proximidade imediata, o método CPX. Por sua vez, para a avaliação do amortecimento do pavimento, foi utilizado o método da impedância mecânica e para a absorção do pavimento o método da impedância acústica. Este trabalho apresenta...

EFFECT OF VANADIUM ON THE DEACTIVATION OF FCC CATALYSTS

Roncolatto,R.E; Lam,Y.L.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/1998 EN
Relevância na Pesquisa
562.8386%
This work provides concrete evidence that vanadium causes the destruction of the zeolite in the FCC catalysts by a mechanism of acid attack or solid-solid transformation, as well as additional dealumination of the zeolite framework in the presence of steam and at high temperature. While these effects resulted in the reduction in crystallinity (zeolite Y content), specific area and unit cell size of the Y zeolite as the amount of vanadium in the catalysts increased, the reduction in activity was the most pronounced. The differences in these behaviors were interpreted and the model can be used for better catalyst formulation or screening.

Effect of temperature on the mechanical properties of polymer mortars

Reis,João Marciano Laredo dos
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2012 EN
Relevância na Pesquisa
782.6754%
This paper presents the results of an experimental program to investigate the effect of temperature on the performance of epoxy and unsaturated polyester polymer mortars (PM). PM is a composite material in which polymeric materials are used to bond the aggregates in a fashion similar to that used in the preparation of Portland cement concrete. For this purpose, prismatic and cylindrical specimens were prepared for flexural and compressive tests, respectively, at different temperatures. Measurements of the temperature-dependent elastic modulus and the compressive and flexural strength were conducted using a thermostatic chamber attached to a universal test machine for a range of temperatures varying from room temperature to 90 ºC. The flexural and compressive strength decreases as temperature increases, especially after matrix HDT. Epoxy polymer mortars are more sensitive to temperature variation than unsaturated polyester ones.

Effect of floor type (dirt or concrete) on litter quality, house environmental conditions, and performance of broilers

Abreu,VMN; Abreu,PG de; Jaenisch,FRF; Coldebella,A; Paiva,DP de
Fonte: Fundação APINCO de Ciência e Tecnologia Avícolas Publicador: Fundação APINCO de Ciência e Tecnologia Avícolas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2011 EN
Relevância na Pesquisa
597.4404%
This study was conducted with the objective of evaluating the use of concrete or hard-packed dirt floor in broiler houses. This experiment was carried out in two different phases. The following performance parameters were studied: live weight, feed intake, feed conversion ratio, and mortality. Litter moisture, pH and temperature were measured. Litter residual contamination after cleaning and disinfection was also evaluated. A dry bulb thermometer, a wet bulb thermometer, and a black bulb thermometer were placed inside each broiler house at bird height and outside the broiler house for data collection. Environmental data were collected at 3h intervals from 00:00 to 24:00 hours during weeks 4, 5, and 6 of the grow-out. Based on the collected data, air relative humidity (RH) was determined, after which wet bulb globe temperature (WBGT) and Radiant Heat Load (RHL) were calculated. There were no differences in live performance parameters. However, total mortality and sudden death were higher in birds raised on dirt floor. On days 0, 14 and 35, litter pH was higher in the dirt floor as compared to the concrete floor, but at the end of the grow-out, this difference disappeared. There was a cubic effect of bird age on litter moisture, which increased up to day 28...

Development of technical bases for using infrared thermography for nondestructive evaluation of fiber reinforced polymer composites bonded to concrete

Starnes, Monica Anastasia
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 258 p.; 14980618 bytes; 14980417 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
595.8517%
Fiber-reinforced polymer (FRP) composites, in the form of pultruded laminates or built-up woven fabrics, are being used widely to strengthen existing concrete and masonry structures. The success of these materials in performing their intended functions depends, to a large extent, on how well they are bonded to themselves and to the substrate. There is a need for an efficient and reliable method to detect and characterize defects at the substrate interface and within multi-ply systems. Infrared thermography is well suited for this purpose because it is inherently sensitive to the presence of near-surface defects and can interrogate large areas efficiently. Before infrared thermography can be developed into a standard methodology, however, an understanding is needed of the effects of testing parameters and different types of defects. This dissertation focuses on establishing the potential for quantitative infrared thermography, that is, not only detecting but also characterizing subsurface flaws. Numerical and experimental methods are used to investigate the effectiveness of infrared thermography to estimate the width of subsurface flaws in fiber-reinforced polymer laminates bonded to concrete. First, a dimensional analysis of a simplified case of one-dimensional heat diffusion in an infinite half space is performed to establish the parameters that affect the thermal response of the test object.; (cont.) The results from the dimensional analysis identified the factors that had to be investigated in the parametric study. Next...

Análise numérica do efeito de fatores influentes da reação álcali-agregado no desempenho de estruturas de concreto; Numerical analysis of the effect of influential factors of alkali-aggregate reaction in the performance of concrete structures

Rodrigues, Edmilson Correia
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Civil; MECÂNICA DAS ESTRUTURAS, ESTRUTURAS DE CONCRETO E ALVENARIA E MATERIAIS E PROCESSOS CONSTRUTIVOS Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Civil; MECÂNICA DAS ESTRUTURAS, ESTRUTURAS DE CONCRETO E ALVENARIA E MATERIAIS E PROCESSOS CONSTRUTIVOS
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
600.94043%
The aim of this work is the numerical simulation of the mechanical performance of concrete affected by Alkali-Aggregate Reaction or RAA, reported by Stanton in 1940. The RAA has aroused attention in the context of Civil Engineering from the early 80, when they were reported consequences of his swelling effect in concrete structures, including cracking, failure and loss of serviceability. Despite the availability of experimental results the problem formulation still lacks refinement so that your solution remains doubtful. The numerical simulation is important resource for the assessment of damages in structures caused by the reaction, and their recoveries The tasks of support of this work were performed by means of the finite element approach, about orthotropic non-linear formulation, and, thermodynamic model of deformation by RAA. The results obtained revealed that the swelling effect of RAA induced decline of the mechanical performance of concrete by decreasing the margin of safety prior to the material failure. They showed that the temperature influences, exclusively, the kinetics of the reaction, so that the failure was the more precocious the higher the temperature of the solid mass of concrete; O objetivo deste trabalho é a simulação numérica do desempenho Mecânico de membros de concreto afetados pela Reação Álcali-Agregado ou RAA...

Effect of transient high temperature on high-strength concrete

Castillo, Carlos
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
504.5264%
The effect of transient high temperature in the uniaxial compressive strength of high strength concrete was investigated. The temperatures studied varied from 100$spcirc$ to 800$spcirc$C. The presence of loads in a structure was simulated by preloading the test specimens during the heating period. Results showed that exposure to temperatures between 100$spcirc$ and 300$spcirc$C decreased the compressive strength of high strength concrete by 15 to 20 percent. For temperatures between 400$spcirc$ and 800$spcirc$C,the compressive strength of concrete decreased to thirty percent of that at room temperature. One third of the preloaded specimens failed explosively during the heating period. In the remaining specimens the presence of a preload had a beneficial effect and a smaller loss of strength was observed compared to unstressed specimens. Exposure to high temperature caused the modulus of elasticity to decrease in all specimens regardlessly of the preload condition and the strength of concrete.

Post-Fire Assessment of Unbonded Post-Tensioned Concrete Slabs: Strand Deterioration and Prestress Loss

MacLean, Kevin J.N.
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 6053766 bytes; application/pdf
EN; EN
Relevância na Pesquisa
506.09562%
Unbonded post-tensioned concrete slabs have been widely used in Canada and the United States since the 1960s, as they allow increased span-to-depth ratios and excellent control of deflections compared to non-prestressed reinforced concrete flexural members. The satisfactory fire performance of unbonded post-tensioned concrete slabs in North America was established by a series of standard fire tests performed in the United States during the 1960s. However, there is a paucity of data on the effect of elevated temperatures on cold-drawn prestressing steel, both in terms of post-fire residual mechanical properties and high-temperature stress relaxation, which can lead to significant prestress loss both during and after a fire. A detailed and comprehensive literature review is presented that provides background on the residual mechanical properties of prestressing steel, as well as on the creep-relaxation behaviour experienced at elevated temperatures under stress. The results of two test series are discussed; the first examining the effects of elevated temperatures on the residual mechanical properties of prestressing steel exposed to elevated temperatures. The second test series examines the irrecoverable and significant loss of prestress force that results from steel relaxation and other thermal effects experienced during heating. A preliminary analytical model is presented...

Colunas mistas esbeltas de aço preenchidas com concreto de alta resistencia em temperatura ambiente e em situação de incendio; Mixed slender steel columns filled with high strenght concrete in room temperature and fire situation

Geraldo Silveira Leite Junior
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 06/02/2009 PT
Relevância na Pesquisa
602.28137%
Neste trabalho, foi investigado em laboratório o efeito do fogo em colunas esbeltas de aço sem preenchimento e preenchidas com concreto de alta resistência que foram submetidas a três diferentes níveis de carga (30%, 50% e 70%). O nível de carga é a razão entre a carga axial a ser aplicada em situação de incêndio e a carga última obtida no ensaio da coluna à temperatura ambiente. Assim sendo, colunas esbeltas de aço sem preenchimento e preenchidas com concreto de alta resistência também foram investigadas à temperatura ambiente, uma vez que os resultados obtidos nessa situação serviram de referência para o estabelecimento das cargas axiais que foram aplicadas em situação de incêndio. Ao todo, foram investigadas 32 colunas esbeltas, sendo 4 sem preenchimento e 4 preenchidas com concreto de alta resistência em temperatura ambiente. Além dessas colunas, 12 foram ensaiadas sem preenchimento e 12 preenchidas com concreto de alta resistência em situação de incêndio. Os valores experimentais de carga última obtidos com as colunas de aço sem preenchimento e preenchidas com concreto de alta resistência à temperatura ambiente e em situação de incêndio foram comparados a aqueles determinados a partir da formulação proposta respectivamente pelo EUROCODE 3 (prEN 1993-1-1:2001)...

Effect of temperature on the durability of systems for strengthening of concrete structures

Vaz, Nelson; Aguiar, J. L. Barroso de; Camões, Aires
Fonte: Thomas Telford Publicador: Thomas Telford
Tipo: Conferência ou Objeto de Conferência
Publicado em //2005 ENG
Relevância na Pesquisa
591.22047%
Nowadays, there is a need in solving problems about the reinforcement of concrete structures. The external reinforcement of concrete with composite materials is a technique that has acquired more and more potential. The bond between reinforcement and support is usually made with epoxy adhesives. However, it is in this part that the integrity of the system can be affected, namely by exposure to high temperatures, amongst various other reasons. In order to study the behaviour of the external reinforcement with the increase of air temperature, several beams were prepared and strengthened with CFRP laminates. After cyclical thermal exposition of 25 days, with maximum temperatures of 20°C, 40°C, 60°C and 80°C, the beams were subjected to bending tests. The results demonstrated that the improvement achieved with the reinforcement, disappears with the increase of the environment's temperature. The thermal resistance of this strengthened system is not very high, thus special needs to be taken into account when applied in warm locations.

Effectiveness of the fineness of two South African Portland cements for controlling early-age temperature development in concrete

Graham,P C; Ballim,Y; Kazirukanyo,J B
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 01/04/2011 EN
Relevância na Pesquisa
604.98387%
Temperature gradients due to heat of hydration of cement can cause cracking and present serious structural and serviceability concerns in concrete structures. Engineers use a wide range of strategies to limit the potential for such cracking, mainly by minimising the maximum temperature in the concrete. This paper considers the possibility of using more coarsely ground cement as one of the strategies for reducing the maximum concrete temperature. Two cement clinkers were used to produce cements with five different levels of fineness. These ten cements were then used to make concretes which were tested in an adiabatic calorimeter to determine the heat evolution characteristics. The measured results were then used in a computational model to calculate the temperature profiles likely to occur in two types of concrete elements. The results indicate that the effect of increasing fineness on the total amount of heat released during hydration is dependent on the mineralogy and crystal composition of the cement clinker. Also, the use of coarse-ground cement as a means of reducing the maximum temperature in concrete is more effective in the case of concrete elements with high cement content but of moderate dimensions. In sections of larger dimension...