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Theses

Caractérisation expérimentale du béton sous fort confinement : influences du degré de saturation et du rapport eau/ciment

Abstract : The objective of this thesis is to experimentally characterize the influence of the saturation ratio and of the water/cement ratio of concrete on its behaviour under high confinement. This thesis lies within a more general scope of the understanding of concrete behaviour under severe loading situations (near field detonation or ballistic impacts). A near field detonation or an impact on a concrete structure generate very high levels of stress associated with complex loading paths in the concrete material. To validate concrete behaviour models, experimental results are required. The work presented in this thesis concerns tests conducted using a static triaxial press that allows to obtain stress levels of the order of the giga Pascal. The porous character of concrete and the high confinement required on the one hand, a development of a specimen protection device, and on the other hand, a development of an instrumentation with strain gauges, which is unprecedented for such high confinements. Hydrostatic and triaxial tests, conducted on the one hand on model materials and on the other hand on concrete, allowed to validate the developed experimental procedures as well as the technique of strain and stress measurements. The studies concerning the influence of the saturation ratio and of the water/cement ratio of concrete on its behaviour required the formulation of a plain baseline concrete and of two modified concretes with different water/cement ratios.
The analysis of triaxial tests performed on the baseline concrete shows that the saturation ratio of concrete has a major influence on its static behaviour under high confinement. This influence is particularly marked for the concrete loading capacity and for the shape of limit state curves for saturation ratios greater than 50%. The concrete loading capacity increases with the confinement pressure for tests on dry concrete wheareas beyond a given confinement pressure, it remains limited for wet or saturated concrete. Concrete failure modes have the form of localization bands. The inclination of these bands evolves with the achieved level of stress in the material, and is oriented perpendicular to the axial direction when this level becomes important.
The analysis of triaxial tests carried out on concretes possessing different water/cement ratios highlights that under low confinement, the concrete behaviour is governed by the cementitious matrix strength. Under high confinement, the concrete behaves like a granular stacking without any influence of the cementitious matrix strength. Thus the limit state curves and the failure modes of concrete are sensitive to its water/cement ratio for low levels of confinement but insensitive to this parameter beyond a critical mean stress.
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Submitted on : Wednesday, April 7, 2010 - 5:26:06 PM
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  • HAL Id : tel-00304343, version 2

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Xuan Hong Vu. Caractérisation expérimentale du béton sous fort confinement : influences du degré de saturation et du rapport eau/ciment. Mécanique [physics.med-ph]. Université Joseph-Fourier - Grenoble I, 2007. Français. ⟨tel-00304343v2⟩

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