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Fresh cement based composite material rheological behaviour
Fibre suspensions properties are used in high performance concrete and cement based materials manufacturing. The fibre introduction, as any additive inclusions whatever its shape, modify the initial fresh material behaviour and this can be in itself a discussed topic but, in the case of fibres, things become even more complicated. As the suspended fibres are slender, their orientation strongly affect the rheological flow properties. In fact, the flow can induce a preferred orientation of the fibres which, upon solidification, strongly influences the mechanical properties of the resulting fibre-reinforced composite. In order to be able to predict this fibre preferred orientation, one needs to have information on the fibre-fluid interaction and on the induced anisotropy influence on the suspension behaviour. The state of the art in polymer reinforcement has been validated in the case of a purely viscous fluid (Glycerol). In the case of cement pastes, it seems that the involved phenomena are the same and that most of the polymer literature concepts may be transposed to cement based composite materials fresh behaviour. It has been demonstrated that there exists a critical amount of fibre that does not depend on the fluid viscosity for which the induced anisotropy will be lower. Apart from the regime around this critical fibre amount, the anisotropy seems correctly predicted by the relation Px(2) x Py(2) = 0.37 l/r. It should be noted that this induced anisotropy only depends on the fibre aspect ratio. Around the critical fibre content, the induced anisotropy is not as strong because of fibre hydrodynamic and mechanical interactions. Just before the critical regime, a small addition of fibres strongly increases the suspension apparent viscosity. Just after the critical regime, a certain amount of fibre may be added with minimum consequences on the viscosity. These are interesting information when choosing a fibre amount in a cement based composite in terms of fresh behaviour. Knowing the viscosity in terms of the mix fitting, one might then calculate the flow of the fresh composite and predict the shear directions assuming that the viscosity anisotropy dependency does not influence too much the flow. Then, knowing the shear directions, one might then predict the fibre anisotropy and the composite mechanical properties in any given direction.
Fresh cement based composite material rheological behaviour
Fibre suspensions properties are used in high performance concrete and cement based materials manufacturing. The fibre introduction, as any additive inclusions whatever its shape, modify the initial fresh material behaviour and this can be in itself a discussed topic but, in the case of fibres, things become even more complicated. As the suspended fibres are slender, their orientation strongly affect the rheological flow properties. In fact, the flow can induce a preferred orientation of the fibres which, upon solidification, strongly influences the mechanical properties of the resulting fibre-reinforced composite. In order to be able to predict this fibre preferred orientation, one needs to have information on the fibre-fluid interaction and on the induced anisotropy influence on the suspension behaviour. The state of the art in polymer reinforcement has been validated in the case of a purely viscous fluid (Glycerol). In the case of cement pastes, it seems that the involved phenomena are the same and that most of the polymer literature concepts may be transposed to cement based composite materials fresh behaviour. It has been demonstrated that there exists a critical amount of fibre that does not depend on the fluid viscosity for which the induced anisotropy will be lower. Apart from the regime around this critical fibre amount, the anisotropy seems correctly predicted by the relation Px(2) x Py(2) = 0.37 l/r. It should be noted that this induced anisotropy only depends on the fibre aspect ratio. Around the critical fibre content, the induced anisotropy is not as strong because of fibre hydrodynamic and mechanical interactions. Just before the critical regime, a small addition of fibres strongly increases the suspension apparent viscosity. Just after the critical regime, a certain amount of fibre may be added with minimum consequences on the viscosity. These are interesting information when choosing a fibre amount in a cement based composite in terms of fresh behaviour. Knowing the viscosity in terms of the mix fitting, one might then calculate the flow of the fresh composite and predict the shear directions assuming that the viscosity anisotropy dependency does not influence too much the flow. Then, knowing the shear directions, one might then predict the fibre anisotropy and the composite mechanical properties in any given direction.
Fresh cement based composite material rheological behaviour
Roussel, Nicolas (author) / Toutou, Zahia (author) / Le Roy, Robert (author)
2004
10 Seiten, 7 Bilder, 2 Tabellen, 15 Quellen
Conference paper
English
Fresh cement based composite material rheological behaviour
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