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Authors
Abstract(s)
No presente trabalho são revistos alguns dos principais métodos de estudo da
composição de betões auto-compactáveis, com especial incidência nos métodos propostos
por Okamura et al., pela JSCE, pelo CBI e pelo LCPC. São também abordados os aspectos
relativos ao desenvolvimento, aos materiais constituintes, às propriedades do betão fresco e
endurecido e ainda à produção e manuseamento do material.
A revisão efectuada permitiu observar que os métodos propostos por Okamura et
al. e pela JSCE são os mais generalizados pela sua simplicidade, mas apresentam algumas
limitações inerentes, associadas à dificuldade em optimizar e modelar as misturas com vista
à obtenção de um qualquer valor médio especificado para a resistência à compressão do
betão na fase de estudo da composição. Em resultado da apreciação efectuada, entendeuse
adequado investigar a possibilidade de se delinear uma nova abordagem ou introduzir
novos parâmetros para o cálculo da composição dos betões auto-compactáveis que
permitissem responder a algumas dessas limitações, admitindo como ponto de partida o
método proposto por Okamura et al.. A proposta a desenvolver deveria assentar em
procedimentos de cálculo expeditos, cuja primeira e fundamental abordagem seria
suportada por ensaios em argamassas, como propôs Okamura.
Analisadas as propostas de diferentes autores, foi definido um intervalo de variação
para cada um dos parâmetros que caracterizam o escoamento das argamassas (Gm e Rm),
conducente à obtenção de betões auto-compactáveis. Para cada família de materiais finos
(i.e., para cada associação de materiais finos), as dosagens de superplastificante e de água
de amassadura que conduziram aos parâmetros Gm e Rm pretendidos, foram determinados
por estudos experimentais em argamassas adoptando uma metodologia que difere
ligeiramente daquela proposta por Okamura et al.. Foram introduzidos novos parâmetros
para quantificar as dosagens de agregados finos (Vp/Vs) nas argamassas e de agregados
grossos (Vm/Vg) nos betões e fizeram-se variar estes parâmetros abaixo e acima dos valores correspondentes propostos por Okamura et al., por forma a avaliar uma possível
optimização das misturas, principalmente através da redução do volume de pasta.
Finalmente, foram analisados os parâmetros que melhor se adequaram ao controlo da
resistência à compressão das argamassas e, indirectamente, ao controlo da resistência dos
betões.
A análise efectuada foi direccionada unicamente para os betões do tipo finos
(solução mais corrente) e apenas foram avaliados os aspectos físicos e mecânicos do seu
comportamento. Foram efectuados estudos em argamassas e betões utilizando associações
binárias e ternárias de materiais finos, que combinaram dois tipos de cimentos (CEM I 42,5R
e CEM II/B-L 32,5N) e quatro adições: fíler calcário, cinzas volantes, sílica de fumo e fíler
granítico.
O fíler granítico utilizado, proveniente de desperdícios industriais, foi testado a título
experimental como adição, com resultados promissores. Sob condições idênticas de
escoamento, o fíler granítico revelou consumos de superplastificante idênticos àqueles
obtidos com as cinzas volantes e fíler calcário (reconhecidamente úteis na produção de
betões auto-compactáveis), enquanto que a sílica de fumo revelou consumos excessivos de
superplastificante, quer em termos absolutos, quer comparativamente às restantes adições.
Os resultados obtidos foram satisfatórios e culminaram com a apresentação de uma
proposta para o estudo do betão auto-compactável do tipo finos, a qual facilita a optimização
da mistura e permite estimar, na fase de estudo da composição, a resistência à compressão
do betão.
Some of the main methods for self-compacting concrete mix design are reviewed in the present research work, with special focus on those proposed by Okamura research group, JSCE, CBI and LCPC. The aspects concerning to development, constituent materials, properties of fresh and hardened concrete and furthermore the production and handling of the material are also reviewed. The bibliographic review have indicated that the methods proposed by Okamura research group and JSCE are the most generalized due to its simplicity, but they present some inherent limitations, associated to its difficulty on optimizing and modelling concrete mixtures in order to achieve a specified mean value for compressive strength defined on the mix design phase. As a result of that appreciation, it was considered adequate to investigate the possibility of outline a new approach or to introduce new parameters for the selfcompacting concrete mix design that allow finding the answer for such limitations, considering, as a start point, the method proposed by Okamura research group. The new proposal should lay on an easy and swift procedure, which, for a start, should be supported by tests on mortar mixes, as proposed by Okamura research group. After the examination of proposals by different authors, an interval of variation was defined for each of the parameters that characterized the flow behaviour of mortars (Gm and Rm), leading to self-compacting concrete mixes. For each family of fine particles, the proportions of superplasticizer and water content which lead to the wanted Gm and Rm parameters were determined by trial mixtures of mortar using a methodology that slightly differ from that proposed by Okamura research group. New parameters were introduced to quantify the proportions of fine aggregate (Vp/Vs) on mortars and to quantify the proportions of coarse aggregate (Vm/Vg) on concretes. Such parameters were changed to values lower and higher than those proposed by Okamura research group, in order to achieve an optimized mixture, namely by reducing the paste volume. Finally, the parameters that better evaluate the mortars compressive strength and, indirectly, the concrete compressive strength were analysed. The analysis done was directed to the powder type self-compacting concrete (the most common solution) and only the physical and mechanical aspects of its behaviour were analysed. Studies on mortar and concrete mixes were made using binary and ternary associations of powder materials which combine two types of cements (CEM I 42,5R and CEM II/B-L 32,5N) and four mineral additions: limestone powder, fly ash, silica fume and granite filer. The granite filer that was used here, originating from a by-product of industry, was tested experimentally as a mineral addition, with promising results. Under identical flow behaviour properties, the granite filer has revealed identical needs of superplasticizer dosages as those of fly ash and limestone powder additions (recognised as advantageous for self-compacting concrete), while the silica fume has revealed overmuch needs of superplasticizer, either in absolute volume, or comparatively with other additions used. The results obtained were satisfactory and ended with the presentation of a proposal for mix design of the type powder self-compacting concrete. This enables the optimization of mixes and, on the mix design phase, allows the estimation of the compressive strength of concrete.
Some of the main methods for self-compacting concrete mix design are reviewed in the present research work, with special focus on those proposed by Okamura research group, JSCE, CBI and LCPC. The aspects concerning to development, constituent materials, properties of fresh and hardened concrete and furthermore the production and handling of the material are also reviewed. The bibliographic review have indicated that the methods proposed by Okamura research group and JSCE are the most generalized due to its simplicity, but they present some inherent limitations, associated to its difficulty on optimizing and modelling concrete mixtures in order to achieve a specified mean value for compressive strength defined on the mix design phase. As a result of that appreciation, it was considered adequate to investigate the possibility of outline a new approach or to introduce new parameters for the selfcompacting concrete mix design that allow finding the answer for such limitations, considering, as a start point, the method proposed by Okamura research group. The new proposal should lay on an easy and swift procedure, which, for a start, should be supported by tests on mortar mixes, as proposed by Okamura research group. After the examination of proposals by different authors, an interval of variation was defined for each of the parameters that characterized the flow behaviour of mortars (Gm and Rm), leading to self-compacting concrete mixes. For each family of fine particles, the proportions of superplasticizer and water content which lead to the wanted Gm and Rm parameters were determined by trial mixtures of mortar using a methodology that slightly differ from that proposed by Okamura research group. New parameters were introduced to quantify the proportions of fine aggregate (Vp/Vs) on mortars and to quantify the proportions of coarse aggregate (Vm/Vg) on concretes. Such parameters were changed to values lower and higher than those proposed by Okamura research group, in order to achieve an optimized mixture, namely by reducing the paste volume. Finally, the parameters that better evaluate the mortars compressive strength and, indirectly, the concrete compressive strength were analysed. The analysis done was directed to the powder type self-compacting concrete (the most common solution) and only the physical and mechanical aspects of its behaviour were analysed. Studies on mortar and concrete mixes were made using binary and ternary associations of powder materials which combine two types of cements (CEM I 42,5R and CEM II/B-L 32,5N) and four mineral additions: limestone powder, fly ash, silica fume and granite filer. The granite filer that was used here, originating from a by-product of industry, was tested experimentally as a mineral addition, with promising results. Under identical flow behaviour properties, the granite filer has revealed identical needs of superplasticizer dosages as those of fly ash and limestone powder additions (recognised as advantageous for self-compacting concrete), while the silica fume has revealed overmuch needs of superplasticizer, either in absolute volume, or comparatively with other additions used. The results obtained were satisfactory and ended with the presentation of a proposal for mix design of the type powder self-compacting concrete. This enables the optimization of mixes and, on the mix design phase, allows the estimation of the compressive strength of concrete.
Description
Keywords
Betão auto-compactável Metodologia - Proporções da mistura Estudo da composição Fase argamassa Reologia Capacidade de escoamento Fluidez - Capacidade de passagem Ensaio de espalhamento Ensaio do funil-V Ensaio da Caixa L Ensaio da Caixa U Ensaio da Caixa Ensaio de compressão Densidade