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‣ Estudo da repassivação da armadura em concretos carbonatados através da técnica de realcalinização química.; Carbonated concrete steel repassivation study through chemical realkalisation technique.

Araújo, Fernanda Wanderley Corrêa 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 14/09/2009 Português
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Esta pesquisa estudou o método de realcalinização química (RAQ), através da absorção e difusão de soluções alcalinas na superfície do concreto carbonatado. Neste estudo foram utilizadas três espécies químicas para obtenção das soluções alcalinas: carbonato de sódio, hidróxido de potássio, e hidróxido de cálcio. Para avaliar a eficácia desta nova técnica de reabilitação, foram realizadas medidas de profundidade de carbonatação e de realcalinização, medidas eletroquímicas de potencial de corrosão e de espectroscopia de impedância eletroquímica (EIE) para a verificação do estado da armadura, ensaios de imersão, absorção e ascensão capilar em concretos de referência, carbonatados e realcalinizados. Em razão da falta de conhecimento sobre a eficácia da técnica de realcalinização eletroquímica (RAE) em relação à repassivação da armadura, em paralelo foi realizado o estudo da repassivação das armaduras na RAE. Em relação à durabilidade da técnica, foi avaliada a resistência do concreto recuperado quando submetido a um novo ciclo de carbonatação acelerada, analisando as novas profundidades de carbonatação para cada solução alcalina estudada. Na repassivação da armadura com a técnica de RAE...

‣ Mitigação da retração autógena em concretos de alta resistência contendo aditivo redutor de retração e seus efeitos na macro e microestrutura; Mitigation of autogenous shrinkage in high strength concrete using shrinkage-reducing admixture and its macro and microstructural effects

Lopes, Anne Neiry de Mendonça
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Tese de Doutorado Formato: application/pdf
Português
Relevância na Pesquisa
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O desenvolvimento do concreto de alta resistência - CAR foi um importante avanço na tecnologia de concreto, entretanto, a despeito de suas inúmeras vantagens como material estrutural, o seu emprego tem sido limitado, por ter se revelado mais susceptível à fissuração nas primeiras idades. Isto se deve à ocorrência do fenômeno da retração autógena, particularmente mais intenso nestes concretos que nos de resistência normal, uma vez que no CAR, há significativamente maior quantidade de material cimentício e menor quantidade de água, o que dá origem a uma estrutura porosa muito refinada logo nas primeiras idades, gerando altas magnitudes de tensões capilares. Além do estudo sobre o entendimento do fenômeno, as pesquisas atualmente têm buscado formas de mitigá-lo a fim de contribuir para estruturas mais duráveis. Diante do exposto, esta pesquisa investigou o comportamento do CAR, no tocante às propriedades mecânicas, elásticas e viscoelásticas e à durabilidade, quando empregado um aditivo redutor de retração - ARR que pode se configurar como estratégia mitigadora para a redução da retração autógena, bem como verificar a sua influência sobre a microestrutura e hidratação da pasta de cimento. Os resultados indicam que o ARR é eficaz na redução da retração autógena e retração por secagem...

‣ Avaliação da durabilidade em vigas de concreto sob diferentes condições de cura e carregamento; Evaluation of durability in concrete beams under different curing conditions and loading

Milton Paulino da Costa Júnior
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 15/12/2010 Português
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A preocupação com a durabilidade do concreto é crescente no Brasil, devido à grande quantidade de estruturas com sinais avançados de deterioração. Aliadas a essa questão têm-se a importância da cura no desempenho do material e as fissuras que podem surgir ao longo de sua vida útil. O objetivo principal deste trabalho foi avaliar a influência da abertura de fissuras induzidas por carregamento e do tipo de cura na durabilidade (profundidade de carbonatação e penetração de cloretos) e microestrutura no concreto. Corpos-de-prova prismáticos de concreto foram produzidos com cimento de alto-forno e submetidos a dois tipos de cura (cura úmida por 7 dias e cura ao ar). Após a cura, os corpos-de-prova ficaram expostos em ambiente externo por 28 dias. Aos 28 dias os corpos-de-prova foram submetidos a duas situações de carregamento e a uma sem carregamento e expostos ao meio ambiente natural e à névoa salina artificial. Nas idades de 6, 12, 18 e 24 meses foram realizados ensaios de profundidade de carbonatação, de penetração de cloretos e análises microestruturais (MEV e EDS). Os resultados obtidos indicaram que aos 24 meses de idade a abertura de fissura aumentou a profundidade de carbonatação nos concretos submetidos à cura ao ar. A cura influenciou nos resultados de profundidade de carbonatação e de penetração de cloretos...

‣ Verification of durability of novel applications

Bragança, L.; Koukkari, Heli
Fonte: Concrete Association of Finland Publicador: Concrete Association of Finland
Tipo: Conferência ou Objeto de Conferência
Publicado em //2006 Português
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Durability of structural concrete can be assessed according to standards, when the degradation models of materials and their combinations as well as experiences from the use are available in a reliable way. In the case of innovative structural materials and applications, the needs to verify durability may lead to extensive studies on the application of current methods. A state-of-the-art of durability verification of functional concrete materials and steel-concrete composite structures shows that existing knowledge is in common adaptable but needs interpretation and systematic identification of risks. However, there are several sources of uncertainty in the methods themselves like e.g. the influence of loading. Further, interaction between different materials inside a structure is in some examples an additional source of chemical reactions and degradation, but the service life design methods typically rely on environmental classes.

‣ Strength and durability characteristics of polymer-modified carbon fiber concrete

Torgal, Fernando Pacheco; Gonzalez, J.; Jalali, Said
Fonte: International Community on Polymers in Concrete (ICPIC) Publicador: International Community on Polymers in Concrete (ICPIC)
Tipo: Conferência ou Objeto de Conferência
Publicado em 12/02/2010 Português
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Carbon-fiber concrete (CFC) materials are gaining momentum due to the reduction of carbon fiber cost and also to the sensing performance of carbon fiber reinforced concrete based structures. For carbon fiber concrete electrical resistance increases with tensile stress and decreases upon compression. Therefore CFC can act as self-monitoring strain sensor. Nevertheless, fiber incorporation is responsible for a loss in concrete workability, and also for a slightly compression strength reduction related to an increase in air content. Although shortterm mechanical properties of these materials are well documented, durability issues still need further investigations efforts. This paper reports some results on the strength and durability characteristics of several concrete mixtures made with different polymer and carbon fiber addition percentage. Results show that carbon fiber addition decreases strength and increases water penetration under pressure and also increases chloride diffusion, while the polymer addition reduces water penetration and concrete permeability.

‣ Sustainable monitoring of concrete structures : strength and durability performance of polymer-modified self-sensing concrete

Torgal, Fernando Pacheco; Gonzalez, J.; Jalali, Said
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Publicado em //2012 Português
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Concrete structures all over the world are reaching the end of their service life sooner than expected. This is due to the fact that ordinary Portland cement-based concrete deteriorates under environmental actions and also that structural inspections and conservation actions are expensive. Besides, as they consume energy and non-renewable resources, they have negative environmental impacts. Self-sensing concrete provides an alternative way of monitoring concrete-reinforced structures at a much lesser cost and with lesser environmental impact. Although the short-term mechanical properties of these materials are usually well documented, the long-term durability issues about carbon fibre concrete still deserve further investigations.This paper reports some investigation of the strength and durability characteristics of several concrete mixtures modified with different percentages of polymer and carbon fibre addition. The results show that the addition of carbon fibre decreases the strength and increases water penetration under pressure and also increases chloride diffusion, whereas polymer addition is responsible for a denser microstructure and higher concrete durability

‣ Using metakaolin to improve the compressive strength and the durability of fly ash based concrete

Torgal, Fernando Pacheco; Shahsavandi, Arman; Jalali, Said
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 22/11/2011 Português
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Partial replacement of Portland cement by pozzolanic and cimentitious by-products or mineral additions that allow for carbon dioxide emission reductions is a major issue in the current climate change context. However, the use of low pozzolanic activity by-products like fly ash can cause a decrease relatively early in compressive strength. In this paper, the effect of metakaolin and fly ash on strength and concrete durability was investigated. The durability was assessed by different means of water absorption, oxygen permeability and concrete resistivity. Results show that partial replacement of cement by 30% fly ash leads to a decrease relevantly early in compressive strength, when compared to a reference mix of 100% Portland cement. Results also show that using 15% fly ash and 15% metakaolin replacement is responsible for minor strength loss but leads to outstanding durability improvement.

‣ Durability of high-performance concrete with fly ash

Camões, Aires; Ferreira, Rui Miguel; Aguiar, J. L. Barroso de; Jalali, Said
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2002 Português
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High-performance concrete (HPC) is usually produced using high quality materials. These high quality constituents drastically increase the initial cost of HPC, hence hindering its more widespread use. Therefore, the main goal of this research project was to produce a low cost enhanced performance concrete or even a low cost HPC, using low quality fly ash and locally available crushed aggregates. In this way, a significant reduction in the use of Portland cement, as well as that of scarce natural resources, would be obtained. The effect of high percentages of fly ash and crushed aggregates on concrete performance was studied by comparing the mechanical and durability performances of such concretes with nominally similar types of concrete with no fly ash incorporated. The results obtained indicate that it is possible to produce concrete in the low range of HPC with up to 65 MPa at 56 days by replacing up to 40% of cement with as received fly ash using crushed granite aggregates. Furthermore, it was observed that workability and durability both increased significantly when fly ash partially replaced Portland cement.

‣ 13th International Congress on Polymers in Concrete

Aguiar, J. L. Barroso de, ed. lit.; Jalali, Said, ed. lit.; Camões, Aires, ed. lit; Ferreira, Rui Miguel, ed. lit.; International Congress on Polymers in Concrete, 13, Madeira, 2010
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /02/2010 Português
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The 13th International Congress on Polymers in Concrete 2010 (13th ICPIC 2010) follows a series of 12 earlier successful congresses, which has been started in London in 1975. These congresses, being held every three years, played a key role in disseminating R&D findings between researchers, academics, industrials and students. The 13th ICPIC was again a forum to exchange knowledge and most recent research findings among participants. It represented a contribution to the development of this important subject. The 13th ICPIC was held in Funchal, capital of Madeira Islands, Portugal. 120 participants coming from thirty different countries presented and discussed about 100 contributions submitted to the congress. The main topics covered had been: (a) Concrete-Polymer Composites (Micro and nanostructure, Ecological aspects, Properties, Test methods and Applications), (b) Interface Zone Polymer/Concrete (Micro and nanostructure, Penetration process, Adhesion strength, Durability and Test methods), (c) Coatings and Crack Injection (Adhesion strength, Permeability, Durability, Test methods and Applications), and (d) Concrete Rehabilitation (Innovations, Durability, Test methods and Case studies). Nowadays, the field “polymers in concrete” is rather consolidated in the construction industry. The future of polymers in concrete will be oriented to take full benefit of the synergic actions between these organic and mineral materials...

‣ Biotech cementitious materials : some aspects of an innovative approach for concrete with enhanced durability

Torgal, Fernando Pacheco; Labrincha, J. A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em 04/01/2013 Português
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The deterioration of reinforced concrete structures is a very common problem due to the fact that this material has a high permeability which allows water and other aggressive media to enter, thus leading to corrosion problems. The use of sealers is a common way of contributing to concrete durability. However, the most common ones are based on organic polymers which have some degree of toxicity. The Regulation (EU) 305/2011 related to the Construction Products Regulation emphasizes the need to reduce hazardous substances. Therefore, new low toxicity forms to increase concrete durability are needed. Recent investigations in the field of biotechnology show the potential of bioinspired materials in the development of low toxic solutions. This paper reviews current knowledge on the use of bacteria for concrete with enhanced durability. It covers the use of bacteria in concrete mix and also biomineralization in concrete surface treatments. Investigation gaps are described. Results from practical applications in which there is exposure to environmental conditions are still needed in order to confirm the importance of this new approach.

‣ Nanoparticles for high performance concrete (HPC)

Torgal, Fernando Pacheco; Miraldo, Sérgio; Ding, Yining; Labrincha, J. A.
Fonte: WoodHead Publishing Ltd Publicador: WoodHead Publishing Ltd
Tipo: Parte de Livro
Publicado em //2013 Português
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According to the 2011 ERMCO statistics, only 11% of the production of ready-mixed concrete relates to the high performance concrete (HPC) target. This percentage has remained unchanged since at least 2001 and appears a strange choice on the part of the construction industry, as HPC offers several advantages over normal-strength concrete, specifically those of high strength and durability. It allows for concrete structures requiring less steel reinforcement and offers a longer serviceable life, both of which are crucial issues in the eco-efficiency of construction materials. Despite the growing importance of nanotechnology, investigations into the incorporation of nanoparticles into concrete are rare (100 out of 10,000 Scopus concrete-related articles published in the last decade). It therefore remains to be seen how research in this area will contribute to concrete eco-efficiency. This chapter summarizes the state of current knowledge in the field and considers the influence of nanoparticles on the mechanical properties of concrete and its durability. It also includes the control of calcium leaching. The problem of efficient dispersion of nanoparticles is analyzed.

‣ Effects of anti-graffiti protection on concrete durability

Neto, Elsa; Souto, Ana; Camões, Aires; Begonha, Arlindo; Cachim, Paulo
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /06/2014 Português
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The patrimony of fair-faced concrete, largely built in the twentieth century and nowadays recognized as heritage to be protected, is susceptible to attacks by graffiti, a form of vandalism that causes a major social and economic impact on society. The concrete is a porous material sometimes deteriorated over the years, and the interactions of the inks and the substrate and removal methods sometimes deteriorate or alter the concrete surface, especially if it is necessary to repeat the removal process. The anti-graffiti products are applied on the surface of the concrete, hindering the adhesion of paints or preventing its penetration into the pores of the concrete, which in turn facilitates their removal. However, it appears that many of the existing protective products on the market also alter the surface characteristics of the concrete irreversibly. Considering that the durability of concrete depends on the composition and characteristics of the surface, it is essential to know the effects of anti-graffiti protection systems on the durability of concrete and contribute to an appropriate methodology to preserve this heritage. Thus, an experimental program was developed for analyzing changes in durability indicators and surface properties that protect concrete from deterioration (i) concrete without protection before and after application of spray paint...

‣ Efeito dos sistemas de proteção anti-graffiti na durabilidade do betão; The effect of anti-graffiti protective coatings on concrete durability

Barata, Ana Cláudia Souto
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Trabalho de Conclusão de Curso
Publicado em //2014 Português
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Dissertação de mestrado integrado em Engenharia Civil; Uma grande parte do património construído no século vinte é em betão aparente, sendo particularmente suscetível às agressões dos graffiti. Devido ao crescente reconhecimento do seu valor e da importância da sua preservação, surgiu a necessidade de adoção de medidas preventivas capazes de minimizar o impacto e deterioração provocados pelos graffiti, bem como pelas sucessivas ações de remoção, no substrato do betão. A aplicação de um novo tipo de tratamento de proteção na superfície de betão foi a solução encontrada para combater este problema. Surgiram assim, os revestimentos de proteção anti-graffiti, permanente e sacrificial, desenvolvidos para proteger as superfícies e dificultar a aderência das pinturas, impedindo a sua fixação profunda, facilitando a sua mesma remoção. Considerando que a durabilidade do betão depende principalmente da sua composição e das características da sua superfície, é importante avaliar quais os efeitos dos produtos de proteção aos graffiti no desempenho e durabilidade do betão aparente. Neste sentido, desenvolveu-se uma campanha experimental com o intuito de analisar as alterações ocorridas nas principais propriedades relacionadas com a durabilidade de dois tipos de betão...

‣ Durabilidade do betão aparente com proteção antigraffiti; Concrete durability with antigraffiti protection

Neto, Elsa; Souto, Ana; Camões, Aires; Begonha, Arlindo; Cachim, Paulo
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /08/2014 Português
Relevância na Pesquisa
48.726%
O património em betão aparente, grande parte construído no século vinte e com um crescente reconhecimento do seu valor e da importância da sua preservação, é suscetível às agressões por graffiti. A durabilidade do betão armado depende da sua composição e das características da sua superfície pelo que é fundamental conhecer quais os efeitos dos sistemas de proteção antigraffiti na durabilidade do betão e contribuir para uma metodologia adequada à preservação deste património. Neste contexto, desenvolveu-se um programa experimental para analisar as alterações das propriedades que protegem a superfície do betão dos mecanismos de deterioração, antes e após o tratamento de proteção antigraffiti, com a proteção antigraffiti e os graffiti e após a sua remoção. Os resultados mostram que os graffiti, a proteção aos graffiti e a remoção dos graffiti afetam as características da superfície do betão.; The heritage of fair-faced concrete, largely built in the twentieth century and nowadays recognized as heritage to be protected, is susceptible to attacks by graffiti. Durability of concrete depends on the composition and characteristics of the surface, whereby it is essential to study the effects of anti-graffiti protection systems on the durability of concrete and adopt the appropriate methodology to preserve this heritage. Thus...

‣ CONTRIBUIÇÃO AO ESTUDO DAS PROPRIEDADES MECÂNICAS E DA DURABILIDADE DE CONCRETOS COM ESCÓRIA DE ACIARIA ELÉTRICA (EAF) COMO AGREGADO GRAÚDO; CONTRIBUTION TO THE STUDY OF MECHANICAL PROPERTIES AND THE DURABILITY OF CONCRETE WITH SLAG OF Residue (EAF) as aggregate

FARIA, Ricardo Andrade Fernandes
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
Português
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The increasing demand for aggregate for uses in engineering stimulated the search for alternative materials. In this way, the civil construction potentially started to be a great consumer of residues from other industries, becoming a great recycle plant. The use of by-product, brings great environmental benefits in relation to the degradation of the environment, as for example, less settlement of residues in earth fill, the reduction of extraction of natural resources, and the exploration of aggregate ores. Steel plants from around the world have a commom problem, that is what to do with all the steel slags generated as a by-product from the steel refining in electric steel plants or oxygen steel plants. There are two points of these process where slags can be generated: the first comes from the electric or oxygen furnace itself (called oxidizing refining) and the second is the laddle metallurgy slag (reduction refining slag), which is the last stage of the steel production. This aims to demonstrate related studies to the use of steel slags (EAF slags) in electric steel plants as coarse aggregate. Expansibility of the steel slag tests had been carried through, compressive strength, tensile strength for diametrical compression, related modulus of deformation and durability tests...

‣ Concreto projetado como revestimento de túneis na Ferrovia Norte-Sul: análise segundo parâmetros de durabilidade; Shotcrete tunnel lining as the Railroad North-South: second analysis parameters durability

MENESES, Antônio Davi Barbosa de
Fonte: Universidade Federal de Goiás; BR; UFG; Mestrado em Geotecnia e Construção Civil; Engenharias Publicador: Universidade Federal de Goiás; BR; UFG; Mestrado em Geotecnia e Construção Civil; Engenharias
Tipo: Dissertação Formato: application/pdf
Português
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The present work aims to analyse the durability parameters of the shotcrete, comparing the dry and wet projection systems, of the concrete resulting from the projection in plates and from the test specimens extracted from the tunnels structures of the North-South Railway, tract 01, in Anápolis-GO. This work considers an experimental research concerning the shotcrete behavior for dry-mix and wet-mix projection systems, by using testing indicators of the main durability parameters coming from national and international specifications. So, the experimental program involves a comparative assessment among the projection systems of current use in shotcrete, considering the comparative analysis between projected plates (control) and extracted test specimens from the tunnels on what refers to meeting the requirements related to durability. Therefore, the experimental program showed as independent variables: type of projection system (whether by means of dry-mix or wet-mix shotcrete) and the extraction of test specimen (from the control plates or from the tunnels structure). For each type of projection (dry-mix and wet-mix shotcrete), three plates were cast (normally used for concrete technological control) in conditions similar to the work-site...

‣ Investigação da deterioração de concretos de uhes por reações com os agregados; Investigation of concrete deterioration from HPPs by reactions involving aggregates

Batista, Danilo Gonçalves
Fonte: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Geotecnia, Estruturas e Construção Civil (EEC); Escola de Engenharia Civil - EEC (RG) Publicador: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Geotecnia, Estruturas e Construção Civil (EEC); Escola de Engenharia Civil - EEC (RG)
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
58.39261%
A long time ago aggregate particles were considered inert but this concept is no longer adequate. Expansive reactions resulting from the oxidation of sulfide-bearing aggregates and the AAR are examples of potential chemical interactions that aggregates may experience in concrete, depending on the surrounding environment. This research is an investigation into concrete deterioration in Hydroelectric Power Plants (HPPs), focusing on aggregate reactions relating to attack by sulfates, due to oxidation of sulfide minerals, as well as to the alkali-aggregate reaction (AAR). One of the main purposes is to have a clearer understanding of the changes in sulfide minerals occurring in aggregates and verify their influence on concrete durability as well as check the conditions and characteristics that maximize or not the synergy of such pathology. Along with that, another purpose is to study the possibility of the AAR occurring in the same structures. To this end, an investigation of concrete structures extracted from five Brazilian hydroelectric plants, namely Corumbá HPP, Marechal Mascarenhas de Moraes HPP, Paulo Afonso II HPP, Paulo Afonso IV HPP and Moxotó HPP, was conducted. In addition to the concretes, a study of the rocky material and aggregates surrounding the plants that were of the same origin as the aggregates in the concretes was also performed. A thorough visual inspection was made in the field of some concrete structures selected from the HPPs ...

‣ Influência do metacaulim na durabilidade de concretos usuais de mercado sujeitos à carbonatação acelerada; Metakaolin influence on market usual concret durability subject to accelerated carbonation

Perim, José Roberto
Fonte: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Geotecnia, Estruturas e Construção Civil (EEC); Escola de Engenharia Civil - EEC (RG) Publicador: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Geotecnia, Estruturas e Construção Civil (EEC); Escola de Engenharia Civil - EEC (RG)
Tipo: Dissertação Formato: application/pdf
Português
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The concrete, to be one of the most consumed material in the world, has been the object of several studies and researches in order to improve and enhance its features with respect to technical, economical and environmental aspects, aiming a higher durability. Solutions have been searched and actions have been implemented in order to produce such concrete and to achieve these goals. One of which is the incorporation of mineral additions to replace part of the Portland cement used in the production of this material. Several additions have been studied over time, among them are the fly ash, the slag blast furnace, the silica fume, the ash from rice husk, the bagasse ash from sugar cane and the metakaolin. The latter is a high reactivity pozzolan and it is being studied to be an alternative material of great potential and abundance, it is found in several parts of the world and it has a great number of advantages, such as ease of exploration, the use of a relatively simple process in its industrialization, the low cost of production and trade, besides a lower environmental impact when compared to the clinker. Several researches have already proved its potential as pozzolanic material, however, a few studies have been conducted in order to verify the durability of concretecurrent market with the addition of metakaolin. The carbonation...

‣ Railway sleepers made of alkali activated fly ash concrete; Durmientes de vías de ferrocarril hechos de hormigón de ceniza volante activadas con álcalis

Palomo, Ángel; Fernández-Jiménez, Ana; López Hombrados, Cecilio; Lleyda, José Luis
Fonte: Universidad Católica de Chile Publicador: Universidad Católica de Chile
Tipo: Artículo
Português
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Nowadays, the tracks that comprise the world railway network are estimated to contain nearly three billion sleepers, over 400 million of which are made of concrete. At the same time, over 50% of the world demand for sleepers (around 20 million units per year) was for the concrete version; and between 2% and 5% of the concrete ties that are laid on tracks every year are to replace or renew worn elements. Concrete durability, however, depends on many factors. And in this context it should be noted that the characteristics of the in-plant industrial process involved in manufacturing precast concrete units differs in a number of ways from in situ construction, vesting these units with properties that distinguish them, in terms of durability, from in situ concrete under the conditions generally prevailing on construction sites. Generally speaking, it is widely admitted that the activation process of fly ashes allows obtaining a material with similar cementing features to those characterising Ordinary Portland Cement. Actually, the alkali activation of fly ashes is a singular procedure by which the powder originated in the power plants is mixed with certain alkaline dissolution and cured under a certain temperature to make solid materials. Contrary to conventional concrete...

‣ Concrete durability standards: International trends and the South African context

Kessy,J G; Alexander,M G; Beushausen,H
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 01/03/2015 Português
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Durability problems in reinforced concrete (RC) structures are an issue of global concern, since they threaten economic growth, natural resources and human safety. As a result, attempts have been made in design standards developed in most countries to include requirements to provide durable RC structures. This paper examines and compares such durability requirements in standards from the United States, Australia, Canada, Europe, India and South Africa. It focuses on aspects such as exposure conditions, limiting values of material compositions and proportions, and cover depth to the reinforcing steel. The paper describes issues behind prescriptive standards and deals with challenges confronting performance approaches for concrete durability. Following international trends, it is evident that the South African Standards, particularly SANS 10100-2, must undergo substantial updating and improvements to durability requirements. The paper suggests the means of re-drafting and implementing durability specifications in any revised version of SANS 10100-2, taking into account both prescriptive and performance alternatives. Further, a methodology of developing durability specifications suitable for the South African concrete industry is proposed...