Politano and Pouquet's law, a generalization of Kolmogorov's four-fifths law to incompres... more Politano and Pouquet's law, a generalization of Kolmogorov's four-fifths law to incompressible MHD, makes it possible to measure the energy cascade rate in incompressible MHD turbulence by means of third-order moments. In hydrodynamics, accurate measurement of third-order moments requires large amounts of data because the probability distributions of velocity-differences are nearly symmetric and the third-order moments are relatively small. Measurements
This article presents the production of strain measurements on porous concrete samples for use in... more This article presents the production of strain measurements on porous concrete samples for use in triaxial compression and extension tests with a very high lateral confining pressure. When a massive concrete structure is subjected to severe loadings (rock falls, near- field detonations, ballistic impacts), the material undergoes triaxial loading at a high confining pressure. To reproduce high levels of stress
Concrete is a building material used for sensitive infrastructures like dams or nuclear reactors;... more Concrete is a building material used for sensitive infrastructures like dams or nuclear reactors; however its behavior remains poorly known under extreme dynamic loading like rock falls, explosions or ballistic impacts. This is due both to the difficulty of reproducing experimentally such a loading which generates transient high triaxial stresses and to the intrinsic complexity of concrete. Predicting its dynamic response needs first an experimental characterization of its behavior under extreme triaxial stresses and various controlled loading paths. Some authors [1] argue that inertia, producing an effective confining stress, plays a major role in the apparent rate dependence in compression. The influence of defects may explain the important rate effect in tension . According to the previous references, identifying the constitutive behavior of concrete under high dynamic loading by means of quasi-static tests is then possible. An experimental study performed on a standard low strength concrete with a maximum aggregate size of 10 mm is presented. The specimens are cylinders of 140 mm length and 70 mm diameter, dried in an oven until weight stabilization. The experimental device consists of a large capacity triaxial press. The experiment originality is due to the level of stresses (of the order of one GigaPascal) regarding the specimen size. "Real" concrete specimens (centimetric aggregate dimension) can then be tested. The use of gauges to measure strains at very high confinement is another original feature of that experimental study. Different loading paths can be followed by means of independent controls of the axial stress and the confining pressure. Several testing programs (hydrostatic, triaxial, proportional, oedometric and extension) have been performed. The influence of moisture content on the triaxial behavior of concrete is presented in another paper . The first results of tests performed on dried specimens presented in this paper highlight different features of the concrete triaxial behavior. They show an influence of the loading path on compaction; we observe both a brittle-to-ductile transition and an evolution of the failure patterns with the confining pressure. A relative independence of the yield surface from the loading path can also be noticed. The extension tests allow us to show the influence of the Lode Angle on the triaxial behavior of concrete.
DYMAT 2009 - 9th International Conferences on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, 2009
This paper concerns the concrete behavior under extreme loading situations (ballistic impacts, pe... more This paper concerns the concrete behavior under extreme loading situations (ballistic impacts, penetration). During such loadings, concrete material is subjected to very high-intensity triaxial stress states. For the purpose of reproducing such stress levels with well-controlled loading paths, static tests have been conducted on concrete samples using a triaxial press offering very high capacities (stress levels of around 1 GPa). This paper is devoted to experimental results which show that the concrete strength in uniaxial compression after 28 days of ageing, f c28 , is a very poor indicator of the high-pressure mechanical response of concrete. From the composition of a reference ordinary concrete (f c28 = 29 MPa), two other concretes have been produced with f c28 equal to 21 MPa and 57 MPa, respectively. Besides, to evaluate the effect of the saturation ratio, Sr, tests have been conducted on both dried samples, wet samples and saturated samples. The results show that contrary to what is observed in simple compression, when placed under high confinement, concrete behaves like a granular stacking. There is no more effect of the cement matrix strength whereas the concrete saturation ratio exerts a major influence.
Concrete Under Severe Conditions, Two Volume Set, 2010
Abstract: This communication concerns the identification of concrete behavior under extreme loadi... more Abstract: This communication concerns the identification of concrete behavior under extreme loading situations (near field detonation or ballistic impacts). In order to reproduce high stress levels with well-controlled loading paths, static tests have been carried out on concrete samples by mean of a very high-capacity triaxial press. The objective of this paper is to quantify the effect of composition of concrete (cement paste volume, aggregate size) on its behavior under static high triaxial loading. The experimental tests results confirm that ...
Concrete Under Severe Conditions, Two Volume Set, 2010
Abstract: This study aims to characterize the mechanical behaviour of light concrete under very h... more Abstract: This study aims to characterize the mechanical behaviour of light concrete under very high stress levels of the order of the Giga Pascal. The studied light concrete, called S800, has low density (800 kilograms per meter cubed) and high measured porosity accessible to water (47%). This paper presents the development of a radial strain measurement device and first tests results obtained on light concrete, using a large capacity triaxial press. These tests results show that the concrete volumetric strain reaches more ...
Science and Technology of Nuclear Installations, 2015
When a concrete structure is subjected to an impact, the material is subjected to high triaxial c... more When a concrete structure is subjected to an impact, the material is subjected to high triaxial compressive stresses. Furthermore, the water saturation ratio in massive concrete structures may reach nearly 100% at the core, whereas the material dries quickly on the skin. The impact response of a massive concrete wall may thus depend on the state of water saturation in the material. This paper presents some triaxial tests performed at a maximum confining pressure of 600 MPa on concrete representative of a nuclear power plant containment building. Experimental results show the concrete constitutive behavior and its dependence on the water saturation ratio. It is observed that as the degree of saturation increases, a decrease in the volumetric strains as well as in the shear strength is observed. The coupled PRM constitutive model does not accurately reproduce the response of concrete specimens observed during the test. The differences between experimental and numerical results can be explained by both the influence of the saturation state of concrete and the effect of deviatoric stresses, which are not accurately taken into account. The PRM model was modified in order to improve the numerical prediction of concrete behavior under high stresses at various saturation states.
This paper proposes a simple formulation for the impact analysis of a deformable projectile on re... more This paper proposes a simple formulation for the impact analysis of a deformable projectile on reinforced concrete targets. This approach assumes the presence of soft strikers and rigid targets. Based on an energy balance, it aims to predict a perforation limit for different targets under soft impacts. The procedure employed is validated by means of tests performed on a rigid target (pendulum test) and reinforced concrete slabs. The article discusses various estimations of the crushing force of projectiles, as derived from experimental results and numerical approaches. The efficiency of simplified approaches is highlighted from an engineering point of view. The limit between soft and hard impacts is also analyzed according to a recent criterion. Moreover, the paper proposes validating the approach using experimental tests with both perforating and non-perforating impact tests on nine slabs.
ABSTRACT Fracture mechanics has attracted much attention from physicists in many decades. Recentl... more ABSTRACT Fracture mechanics has attracted much attention from physicists in many decades. Recently, several remarkably universal features in the fracture process have been discovered, including the anisotropy of fracture surface roughness in directions parallel and perpendicular to the crack propagation, as well as the the self-affinity of the crack surface. It has been shown that the crack surface can be described by a roughness parameter called the Hurst exponent, H, whose value is largely debated in the literature [1]. However, the physical role played by the heterogeneities in concrete (i.e., the hard inclusions) in relation to crack roughness is not well understood. The fundamental challenge is here to understand how the development of instabilities for a dynamic propagating crack front within a disordered media. The aim of this presentation is to investigate via the lattice beam method the scaling properties of fracture in concrete samples without and with hard inclusions. Our lattice is a mesoscale representation of concrete and we focus on mode I cracks. This type of study has essentially been realized by discrete lattice method in two-dimensions or in three-dimensions with quasistatic fuse model [2]. To capture and explain the interplay between disorder and dynamical effects at a mesoscopic scale, we simulate the fracture process from a random three-dimensional lattice beam network developed by G. Lilliu et al. [3], where the aggregate particles are included as spherical grains. Moreover, to satisfy the large computational demand of the discrete-element method, the lattice model based on Bernouilli beams theory is implemented in an open source parallel code. Our results demonstrate the capacity of the 3D beam lattice model to capture the anisotropy of the fracture surface roughness and to estimate the Hurst exponent. We also exhibit the influence of the hard inclusions on the self-affine properties of the crack surface.
Politano and Pouquet's law, a generalization of Kolmogorov's four-fifths law to incompres... more Politano and Pouquet's law, a generalization of Kolmogorov's four-fifths law to incompressible MHD, makes it possible to measure the energy cascade rate in incompressible MHD turbulence by means of third-order moments. In hydrodynamics, accurate measurement of third-order moments requires large amounts of data because the probability distributions of velocity-differences are nearly symmetric and the third-order moments are relatively small. Measurements
This article presents the production of strain measurements on porous concrete samples for use in... more This article presents the production of strain measurements on porous concrete samples for use in triaxial compression and extension tests with a very high lateral confining pressure. When a massive concrete structure is subjected to severe loadings (rock falls, near- field detonations, ballistic impacts), the material undergoes triaxial loading at a high confining pressure. To reproduce high levels of stress
Concrete is a building material used for sensitive infrastructures like dams or nuclear reactors;... more Concrete is a building material used for sensitive infrastructures like dams or nuclear reactors; however its behavior remains poorly known under extreme dynamic loading like rock falls, explosions or ballistic impacts. This is due both to the difficulty of reproducing experimentally such a loading which generates transient high triaxial stresses and to the intrinsic complexity of concrete. Predicting its dynamic response needs first an experimental characterization of its behavior under extreme triaxial stresses and various controlled loading paths. Some authors [1] argue that inertia, producing an effective confining stress, plays a major role in the apparent rate dependence in compression. The influence of defects may explain the important rate effect in tension . According to the previous references, identifying the constitutive behavior of concrete under high dynamic loading by means of quasi-static tests is then possible. An experimental study performed on a standard low strength concrete with a maximum aggregate size of 10 mm is presented. The specimens are cylinders of 140 mm length and 70 mm diameter, dried in an oven until weight stabilization. The experimental device consists of a large capacity triaxial press. The experiment originality is due to the level of stresses (of the order of one GigaPascal) regarding the specimen size. "Real" concrete specimens (centimetric aggregate dimension) can then be tested. The use of gauges to measure strains at very high confinement is another original feature of that experimental study. Different loading paths can be followed by means of independent controls of the axial stress and the confining pressure. Several testing programs (hydrostatic, triaxial, proportional, oedometric and extension) have been performed. The influence of moisture content on the triaxial behavior of concrete is presented in another paper . The first results of tests performed on dried specimens presented in this paper highlight different features of the concrete triaxial behavior. They show an influence of the loading path on compaction; we observe both a brittle-to-ductile transition and an evolution of the failure patterns with the confining pressure. A relative independence of the yield surface from the loading path can also be noticed. The extension tests allow us to show the influence of the Lode Angle on the triaxial behavior of concrete.
DYMAT 2009 - 9th International Conferences on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, 2009
This paper concerns the concrete behavior under extreme loading situations (ballistic impacts, pe... more This paper concerns the concrete behavior under extreme loading situations (ballistic impacts, penetration). During such loadings, concrete material is subjected to very high-intensity triaxial stress states. For the purpose of reproducing such stress levels with well-controlled loading paths, static tests have been conducted on concrete samples using a triaxial press offering very high capacities (stress levels of around 1 GPa). This paper is devoted to experimental results which show that the concrete strength in uniaxial compression after 28 days of ageing, f c28 , is a very poor indicator of the high-pressure mechanical response of concrete. From the composition of a reference ordinary concrete (f c28 = 29 MPa), two other concretes have been produced with f c28 equal to 21 MPa and 57 MPa, respectively. Besides, to evaluate the effect of the saturation ratio, Sr, tests have been conducted on both dried samples, wet samples and saturated samples. The results show that contrary to what is observed in simple compression, when placed under high confinement, concrete behaves like a granular stacking. There is no more effect of the cement matrix strength whereas the concrete saturation ratio exerts a major influence.
Concrete Under Severe Conditions, Two Volume Set, 2010
Abstract: This communication concerns the identification of concrete behavior under extreme loadi... more Abstract: This communication concerns the identification of concrete behavior under extreme loading situations (near field detonation or ballistic impacts). In order to reproduce high stress levels with well-controlled loading paths, static tests have been carried out on concrete samples by mean of a very high-capacity triaxial press. The objective of this paper is to quantify the effect of composition of concrete (cement paste volume, aggregate size) on its behavior under static high triaxial loading. The experimental tests results confirm that ...
Concrete Under Severe Conditions, Two Volume Set, 2010
Abstract: This study aims to characterize the mechanical behaviour of light concrete under very h... more Abstract: This study aims to characterize the mechanical behaviour of light concrete under very high stress levels of the order of the Giga Pascal. The studied light concrete, called S800, has low density (800 kilograms per meter cubed) and high measured porosity accessible to water (47%). This paper presents the development of a radial strain measurement device and first tests results obtained on light concrete, using a large capacity triaxial press. These tests results show that the concrete volumetric strain reaches more ...
Science and Technology of Nuclear Installations, 2015
When a concrete structure is subjected to an impact, the material is subjected to high triaxial c... more When a concrete structure is subjected to an impact, the material is subjected to high triaxial compressive stresses. Furthermore, the water saturation ratio in massive concrete structures may reach nearly 100% at the core, whereas the material dries quickly on the skin. The impact response of a massive concrete wall may thus depend on the state of water saturation in the material. This paper presents some triaxial tests performed at a maximum confining pressure of 600 MPa on concrete representative of a nuclear power plant containment building. Experimental results show the concrete constitutive behavior and its dependence on the water saturation ratio. It is observed that as the degree of saturation increases, a decrease in the volumetric strains as well as in the shear strength is observed. The coupled PRM constitutive model does not accurately reproduce the response of concrete specimens observed during the test. The differences between experimental and numerical results can be explained by both the influence of the saturation state of concrete and the effect of deviatoric stresses, which are not accurately taken into account. The PRM model was modified in order to improve the numerical prediction of concrete behavior under high stresses at various saturation states.
This paper proposes a simple formulation for the impact analysis of a deformable projectile on re... more This paper proposes a simple formulation for the impact analysis of a deformable projectile on reinforced concrete targets. This approach assumes the presence of soft strikers and rigid targets. Based on an energy balance, it aims to predict a perforation limit for different targets under soft impacts. The procedure employed is validated by means of tests performed on a rigid target (pendulum test) and reinforced concrete slabs. The article discusses various estimations of the crushing force of projectiles, as derived from experimental results and numerical approaches. The efficiency of simplified approaches is highlighted from an engineering point of view. The limit between soft and hard impacts is also analyzed according to a recent criterion. Moreover, the paper proposes validating the approach using experimental tests with both perforating and non-perforating impact tests on nine slabs.
ABSTRACT Fracture mechanics has attracted much attention from physicists in many decades. Recentl... more ABSTRACT Fracture mechanics has attracted much attention from physicists in many decades. Recently, several remarkably universal features in the fracture process have been discovered, including the anisotropy of fracture surface roughness in directions parallel and perpendicular to the crack propagation, as well as the the self-affinity of the crack surface. It has been shown that the crack surface can be described by a roughness parameter called the Hurst exponent, H, whose value is largely debated in the literature [1]. However, the physical role played by the heterogeneities in concrete (i.e., the hard inclusions) in relation to crack roughness is not well understood. The fundamental challenge is here to understand how the development of instabilities for a dynamic propagating crack front within a disordered media. The aim of this presentation is to investigate via the lattice beam method the scaling properties of fracture in concrete samples without and with hard inclusions. Our lattice is a mesoscale representation of concrete and we focus on mode I cracks. This type of study has essentially been realized by discrete lattice method in two-dimensions or in three-dimensions with quasistatic fuse model [2]. To capture and explain the interplay between disorder and dynamical effects at a mesoscopic scale, we simulate the fracture process from a random three-dimensional lattice beam network developed by G. Lilliu et al. [3], where the aggregate particles are included as spherical grains. Moreover, to satisfy the large computational demand of the discrete-element method, the lattice model based on Bernouilli beams theory is implemented in an open source parallel code. Our results demonstrate the capacity of the 3D beam lattice model to capture the anisotropy of the fracture surface roughness and to estimate the Hurst exponent. We also exhibit the influence of the hard inclusions on the self-affine properties of the crack surface.
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