A new experimental technique for the analysis of concrete under high triaxial loading (original) (raw)
Related papers
Strength and damage of concrete under high triaxial loading
European Journal of Environmental and Civil Engineering, 2010
This study focuses on identifying concrete behavior under severe loading (near field detonation or ballistic impacts). In order to reproduce high stress levels with well-controlled loading paths, static tests are carried out on concrete samples by mean of a very high-capacity triaxial press. Experimental results indicate a sizeable change in concrete behavior with confining pressure. At low pressure values, the concrete exhibits brittle behavior with failure caused by a localized damage mechanism. In contrast, at high ...
Concrete behavior under very high stresses
This communication concerns the concrete behavior under extreme loading situations (near field detonation or ballistic impacts). During such loadings, concrete material is subjected to very high-intensity triaxial stress states. The validation of concrete behavior models, which simultaneously take into account the phenomena of brittle damage and irreversible strain such as compaction, thus requires test results that enable reproducing complex loading paths. Since 2004, the University of Grenoble has launched in collaboration with the French Ministry of Defense (DGA, Centre d'Etudes de Gramat) a research program on the vulnerability of concrete infrastructures. This presentation is devoted to the results of this program. Triaxial tests on a low-strength plain concrete have been performed, using a large capacity triaxial press named "GIGA". Stress levels overpassing one GigaPascal with homogeneous, static and well controlled loading paths have been reached. 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 not any influence of the level of the cement matrix strength whereas the saturation ratio exerts a major influence. The concrete strength capacity can be divided by 5 if the concrete is saturated instead of dried.
Cement and Concrete Research, 2008
The aim of this study is to characterize the behaviour of concrete under high triaxial loading at levels of confinement and axial stress of the order of the GigaPascal. This study is carried out within a more general scope of understanding concrete behaviour under impact. The studied concrete has properties as close as possible to those used in current construction projects. A triaxial press of high capacity is used to characterize the triaxial behaviour of concrete according to various loading paths. Hydrostatic, triaxial, proportional and oedometric tests are performed and show the influence of the loading path on the compaction process. The triaxial and proportional tests show the existence of strain limit states, defining a limit states threshold independent from the loading path.
2006
Concrete is a building material used for sensitive infrastructures (dams, nuclear reactors), however its behaviour under extreme dynamical loading (rock falls, explosions, ballistic impacts) remains poorly known. This is due both to the difficulty of experimentally reproducing such a loading and to the intrinsic complexity of concrete behaviour. In order to predict its response under dynamic loading the experimental characterization of its static behaviour in compression under very high confinement is needed. In this paper a new large capacity triaxial press and the manufacturing and testing procedures developed to perform the tests are presented. Low strength plain concrete specimens were subjected to triaxial and proportional loading paths up to an ultimate state associated to failure. The influence of the loading path on the observed limit state of concrete subjected to multiaxial stress states will then be discussed.
The Journal of Strain Analysis for Engineering Design, 2009
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 (e.g. rock falls, near-field detonations, and ballistic impacts), the material undergoes triaxial loading at a high confining pressure. To reproduce high levels of stress with well-controlled loading paths, static tests are carried out on concrete using a high-capacity triaxial press, called GIGA. This press allows the testing of concrete specimens (7 cm in diameter and 14 or 15.5 cm long) for levels of confining pressure ranging up to 850 MPa and axial stresses of up to 2.35 GPa. The porous characteristic of the material together with the high confining pressure require both developing a material protection device and building strain gauge-based instrumentation of unprecedented design for such confining pressures. In addition, the effect of pressure and other sources of error on strain and stress measurements are identified herein thanks to tests performed on model materials. This study shows that the effect of pressure on strain gauge measurements is negligible, whereas this same effect proves significant in the axial displacement measurement by means of a linear variable differential transformer (LVDT) sensor and must be taken into account therefore during the data processing phase. This article will present the initial results of triaxial compression tests conducted at high confining pressure on both dry and saturated concrete samples instrumented with gauges. It will also provide results of a triaxial extension test conducted at high confinement on dry concrete: a unique step in characterizing the triaxial behaviour of concrete. Moreover, it will be demonstrated that simultaneous axial strain measurements using gauges and the LVDT sensor serve to evaluate strain homogeneity of the sample tested at high confinement.
Experimental analysis of concrete behavior under high confinement: Effect of the saturation ratio
International Journal of Solids and Structures, 2009
This study focuses on the identification of concrete behavior under severe triaxial loading in order to better evaluate the vulnerability of sensitive infrastructure to near-field detonations or ballistic impacts. For the purpose of reproducing high 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). It is a well-known fact that the concrete drying process is a slow phenomenon. Massive concrete structures, such as bridge piers, dams and nuclear reactors, could retain a quasi-saturated core throughout most of their lifetime, even though their facing dries very quickly. The objective of this article is to evaluate the effect of the saturation ratio on concrete behavior under high confinement; this article will present triaxial test results on concrete samples over a saturation ratio range extending from dried to quasi-saturated concretes. The subsequent analysis of results will show that the saturation ratio exerts a major influence on concrete behavior, particularly on both the concrete strength capacity and shape of the limit state curve for saturation ratios above 50%. This analysis also highlights that while the strength of dried concrete strongly increases with confining pressure, it remains constant over a given confining pressure range for either wet or saturated samples.
Experimental Study of Plain Concrete under Triaxial Stress
ACI Materials Journal, 1996
The mechanical behavior of plain concrete under triaxial stress states was investigated experimentally to establish the sensitivity of the mechanical properties to an array of physical and experimental variables, and to enhance the available database of such tests for the benefit of improved understanding and modeling of the constitutive behavior of the material. The test program was particularly focused on the deformation aspects of the response and the process of damage buildup, and consisted of 130 different tests. Parameters of the experimental program were the porosity of concrete, the moisture content at the time of testing, and the load path used in the tests. The most important response index was the history of damage accumulated in the microstructure, which was measured in terms of volumetric expansion and plastic deformation of the material. A simple strain-based model was formulated to represent the experimental trends. It was shown that the expansive strain of the cross section supporting the compressive strut best organized the experimental data. This result indicates that expansion due to damage is responsible for the stiffness degradation and the softening of resistance that is observed in concrete with increasing deformation levels; hence, this is one of the most important state variables characterizing the constitutive behavior of the material.
Journal De Physique Iv, 2006
Knowledge of the behaviour of geomaterials under confined compression is a pre-requisite for any analysis of their ballistic performance. This study proposes an experimental method of determining the spherical and deviatoric behaviour of these materials under high pressure. Known as the 'quasi-oedometric compression test' it consists of compressing a cylindrical specimen tightly enclosed in a thick confinement vessel. The principles of these quasi-oedometric tests are given first, and the steps taken for their execution, together with an examination of the steel used for the confinement vessel. An original way of analysing the data of the test is presented and validated by numerical simulations. These calculations provide valuable information about the influence of the interface product introduced between the vessel and the specimen, and that of friction. Tests are then presented with specimens of aluminium alloy to validate the experimental set-up and the method of analysis. In addition, quasi-oedometric compression tests of cement based material, with and without particles, illustrate the opportunities offered by this testing method, and show that its deviatoric strength and compaction law are significantly improved by ceramic granulates addition.
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, 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.