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Limit state points as contraction-dilatancy transitions on the volumetric behavior curves plotted in the stress space (σ m, q) with associated failure facies: () Monotone triaxial tests (o) Cyclic triaxial tests (+) Proportional tests (see Gabet et al. 2008 for details on these tests).
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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 concre...
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Citations
... The experimental quasi-static EOS of cementitious materials may be obtained from tri-axial hydrostatic tests [47][48][49] or uniaxial confined (oedometric [47,50-53]) tests. The oedometric test technique that is based on uniaxial strain conditions in the tested specimens is more affordable and is technically simpler. ...
... The oedometric test technique that is based on uniaxial strain conditions in the tested specimens is more affordable and is technically simpler. The oedometric test has been proven to provide quality results at a large pressure range up to~1 GPa [48][49][50][51][52]. Note that although the EOS is produced by quasi-static loading, it may be implemented for dynamic analysis and used in "hydro-codes", as is widely done in different commercial software (i.e., ANSYS AUTODIN [54] and LS-DYNA [55]), where strain-rate effect is introduced in the deviatoric component, while the EOS does not exhibit a strain-rate effect (i.e., P-a model [56], that is recommended for cementitious materials). ...
This paper aims at investigating the triaxial behavior of Autoclaved Aerated Concrete (AAC) under extremely high pressures, and experimentally determine Equation of State (EOS) for several different AAC densities. Oedometric tests were carried out using a home-made high-pressure triaxial apparatus, and pressures up to ~500 MPa were applied. The complete pressure-bulk strain relationships were measured, and new findings and insights were obtained. The paper presents the testing set-up and the measurement system. The data processing method accounting for the AAC pronounced shortening during the ongoing test is described using a weighted functions procedure for the circumferential strains’ calculation, with which the confining pressure was determined. The boundary conditions effects on the test results were investigated, and a new technique for specimen insulation was suggested to ensure loading without friction and the prevention of local shear failure. The experimental EOS for different AAC densities were obtained. EOS curves for different specimens with the same density demonstrated good to very good repeatability of the EOS curves over the entire pressure range. Based on the tests results and the density’s span, three classes of AAC are proposed. A preliminary attempt to apply the newly obtained EOS curves has been carried out to examine the energy dissipation for three different dynamic load levels. Although this is a preliminary stage that is beyond the objective of this paper, early interesting results were observed where an optimal AAC density, for which the highest energy has been absorbed, was identified. This finding encourages inclusion of that preliminary study as a closure section. Numerical simulations of wave propagation through ACC layers of different densities, laid on rigid supporting slabs, was carried out. The minimum total impulse imparted to the rigid slab was found for the optimal AAC density that has been determined above.
... Compared to the isotropic tests, the oedometric (confined uniaxial) tests are more affordable, because the specimen is inserted into a confining cylinder and pressure is applied in the axial direction, whereas the cylinder's support provides the lateral confining pressure. Thus, it provides a simpler option to study the EOS at a similarly high axial pressure level [30][31][32][33][34]. An oedometric test requires a similarly highcapacity actuator and stiff confining cylinder, but enables testing of larger specimens [5,[31][32][33][34][35]. ...
... Thus, it provides a simpler option to study the EOS at a similarly high axial pressure level [30][31][32][33][34]. An oedometric test requires a similarly highcapacity actuator and stiff confining cylinder, but enables testing of larger specimens [5,[31][32][33][34][35]. It should be noted that in an oedometric test, both hydrostatic and deviatoric components are developed. ...
High intensity impact loading on a concrete structure induces three dimensional high intensity stresses, the analysis of which requires appropriate constitutive relationships describing the isotropic and deviatoric stress components. The isotropic component known as the hydrostatic relationship or the equation of state (EOS) is in the focus of this paper. The literature relates the EOS of concrete to its uniaxial compressive strength. This paper aims at refuting this relationship and validating the conjecture that the EOS depends on the concrete mixture. For that purpose, different concrete mixes of equal strength have been tested. The mixture parameters are the water content (with the same w/c ratio), the coarse aggregate content and the maximum aggregate size. Using a unique test setup, hydrostatic tests were carried out to extremely high pressures at the 1GPa level. The results clearly show the pronounced differences between EOS curves representing different mixtures having the same concrete strength, thus validating the above conjecture. As the EOS is sometimes derived from oedometric tests, the present investigation exploited oedometric tests results on exactly the same concrete mixtures and strength to compare the hydrostatic and oedometric resulted EOS curves. The comparisons show that for most cases the stress at a certain volumetric strain in the oedometric curves are somewhat lower than these in the hydrostatic EOS curves. However, for mixes with a large maximum aggregate size with a high aggregate content, the oedometric EOS merges with the hydrostatic EOS curves in the mid-to high pressure levels. Finally, statistical analysis using Analysis of Variance has been employed to identify the effect of different mixture parameters and their combination on the differences in the EOS. These new results enhance the insight on concrete behavior under triaxial high pressures and contribute to the development of a new generation of EOS curves.
... To better understand complex phenomena such as brittle damage, compaction under very high confining pressure (up to 650 MPa), and the strain rate effects, multiple experimental studies have been conducted on widely investigated R30A7 concrete (σ c = 30 MPa at 28 days). Previous studies aimed to understand the effect on the concrete behav- [12,19,20,25,38], of saturation and water-to-cement ratios [37], of coarse aggregates shape and composition [30,31], of initial matrix porosity [26], and of water interstitial pore pressure [1]. Spalling experiments were also performed to evaluate the high strain rate tensile strength of concrete [13,15].The results have proved that the unconfined compressive strength is a poor indicator of the high-pressure mechanical response of concrete, and that the water saturation ratio is an important parameter governing the triaxial compressive strength of concrete. ...
Concrete structures are widely used as shielding barriers to protect sensitive infrastructures. Possible accidental conditions such as aircraft impacts on nuclear containment have led to an increasing demand for advanced design of concrete structures under extreme loading. Several studies have shown that the presence of free water in concrete significantly affects its response when subjected to static loading with high mean stresses or dynamic loading with high strain rates. Therefore, the aim of this paper is to investigate the influence of the saturation ratio on perforation and penetration of concrete. To achieve this purpose, the study will simulate the impact of ogive-nosed steel projectile on three plain concrete targets, passively confined by means of steel jackets surrounding the cylindrical specimens.
... Furthermore, instead of uniaxial compression, high-speed projectile intrusion into the specimen response is tri-axial [1]. Due to triaxial stress, the material response differs under high-speed impact loading [32]. This paper presents a comparison of the responses of conventional mortar mixture with cementitious materials prepared by replacing sand with 30 % WTR. ...
... A triaxial hydrostatic experiment is essential for the determination of the pore collapse evolution parameters. Triaxial testing of concrete requires apparatus with high-pressure capacity such as a GIGA press described in Malecot et al. (2010). Consequently, the available experimental data are limited. ...
... For this reason, we estimated the pore collapse evolution parameters from data found in Figure 7. Engineering stress-strain curves of quasi-static compression (left) and tension (right). Malecot et al. (2010) and Magellanes et al. (2010). The pore collapse evolution parameters are the crush pressure P crush ¼ f c 3 ≈ 24:3 MPa, the solidification pressure P lock ¼ 500 MPa, the solidification bulk modulus K 1 ¼ 1:5 Á K 0 ¼ 35 GPa, the crush volumetric strain μ crush ¼ P crush =K 0 ¼ 1:04 Á 10 À3 and the fully compacted volumetric strain μ lock ¼ 0:057714. ...
Concrete is used for protective structures all over the world. Accurate response estimates to a given threat is vital for designing such structures. Concrete models often require numerous input parameters for which sufficient experimental data can be challenging to obtain. Some models are accompanied by parameter generators which use the unconfined compression strength to extrapolate the remainder of the parameters based on experimental databases. This study investigates simulation of ballistic impact on high-strength concrete with 75 MPa nominal unconfined cylindrical compressive strength. The first objective is to investigate the accuracy parameter generators to produce input data for commonly used concrete material models. The second objective is to establish and evaluate a simplified parameter calibration procedure based on standard material experiments and data from the literature. The results employing parameter generators varied notably between the models while still giving decent ballpark estimates. The parameters obtained from inverse modelling of standardized material tests improved the results significantly. The findings of this study recommend caution when using automatic parameter generators. Although a detailed calibration of these concrete models is complicated, a simplified calibration gives reasonable predictions, making this the advisable approach for designing concrete protective structures.
... Furthermore, instead of uniaxial compression, high-speed projectile intrusion into the specimen response is tri-axial [1]. Due to triaxial stress, the material response differs under high-speed impact loading [32]. This paper presents a comparison of the responses of conventional mortar mixture with cementitious materials prepared by replacing sand with 30 % WTR. ...
... While, loading path and confining pressure conditions can significantly affect the mechanical properties of concrete [14,15]. In terms of concrete failure mode, researchers found that confining pressure can significantly improve the strength characteristics of concrete, and with the increase of confining pressure, concrete changes from obvious brittle failure to significant ductile failure [16]. Researchers have established a concrete triaxial compression strength calculation model related to the mix proportion, and found that the model can effectively calculate the ultimate strength of concrete under triaxial compression [17]. ...
Based on engineering practice and practical needs, this paper takes ordinary concrete specimens as the research object, and adopts a high-temperature true triaxial loading test system to carry out high-temperature uniaxial and true triaxial static compression tests of concrete under high-temperature conditions. By comparing with normal temperature conditions, this paper analyzes the influence of the coupling effect of high-temperature and biaxial unequal lateral pressure on the static mechanical properties of concrete. By analyzing the experimental data, we reached a series of conclusions and carried out theoretical research on this basis. High temperatures can significantly affect the uniaxial static pressure strength characteristics, deformation characteristics, and failure mode of concrete. When the temperature exceeds 400 °C, the compressive strength decreases significantly, the peak strain increases sharply, and the plasticity of concrete is further enhanced. The coupling effect of high-temperature deterioration and lateral pressure strengthening makes the true triaxial mechanical properties of concrete change significantly; 0.6:0.2 and 400 °C are the turning points of side pressure ratio and temperature that affect the change law of the true triaxial mechanical properties of concrete, respectively. Based on the study of the high-temperature deterioration factor and lateral pressure strengthening factor, this paper further puts forward a concrete strength formula under the coupling action of high temperature and biaxial unequal lateral pressure. It was verified that the formula has a high accuracy.
... Under confined compression and increasing mean stress levels, concrete first follows a linear behavior, and then its tangent stiffness decreases due to the cement matrix damage, which leads to porosity closure. During the porosity closure, the stiffness of the material increases and tends to the elastic stiffness of the fully consolidated material Malecot et al. (2010). This behavior at the macroscopic scale can be reproduced through simple interaction laws between DE. ...
... Cette forme est affichée jusqu'à la rupture totale de l'éprouvette. Des cônes de matériau sont alors observés au niveau des extrémités, comme expérimentalement [82]. De plus, une comparaison des réponses contrainte-déformation des deux essais de compression est effectuée en figure 3.15. ...
Bien que de nombreux travaux se soient intéressés à la modélisation des mécanismes de rupture des matériaux fragiles et quasi-fragiles, des lacunes dans la compréhension des processus de rupture persistent. Dans le but de progresser sur la compréhension de ces mécanismes, le travail de recherche mené dans le cadre de cette thèse consiste en la combinaison de plusieurs méthodes largement utilisées pour modéliser les problèmes de rupture. En effet, le modèle développé dans cette thèse s’inspire de la mécanique non linéaire de la rupture, en particulier les modèles de zone cohésive, couplée à une méthode numérique discrète. Ce modèle consiste en particulier en l’introduction, dans le code aux éléments discrets GranOO, d’un lien cohésif de type poutre endommageable de lattice dont l’endommagement et par conséquent la rupture sont pilotés énergétiquement. Les équations issues de la théorie des poutres d’Euler-Bernoulli régissant le comportement des liens sont ainsi enrichies d’une phase adoucissante, inspirée des modèles de zone cohésive, s’appuyant sur une équivalence entre les cinématiques de la poutre d’Euler-Bernoulli et les modes de ruptures conventionnels. Cette équivalence conduit à la définition de deux pseudo-modes de rupture. Le premier nommé pseudo Mode I est basé sur l’élongation du premier ordre de la poutre de lattice liée aux sollicitations de traction tandis que le pseudo Mode II est quant à lui basé sur les élongations du second ordre engendrées par les sollicitations de flexion, cisaillement et torsion.Le caractère atypique de ce modèle a mené à de solides phases de calibration et validation. Dans un premier temps, le modèle est calibré par l’intermédiaire de deux essais, un essai de traction simple et un essai de compression simple menés sur un matériau quasi-fragile de type mortier (béton de sable). La modélisation de l’essai de compression montre alors une prédisposition du modèle à rendre compte de l’effet des conditions aux limites de l’essai sur les chemins de fissuration qui sera plus amplement vérifiée par la suite.Dans un second temps, le modèle est éprouvé via la simulation d’un essai de traction-compression et d’un essai brésilien permettant de vérifier la capacité du modèle à rendre compte respectivement de l’effet unilatéral et de la cinétique de propagation de fissure. Enfin, le modèle de poutre endommageable de lattice est confronté à des essais expérimentaux plus complexes. D’une part, les différents essais proposés dans le benchmark Carpiuc sont simulés. La simulation d’éprouvettes de mortier entaillées soumises à des sollicitations simultanées de traction, cisaillement et flexion permettent d’évaluer les capacités du modèle à décrire des chemins de fissuration (bifurcation et branchement) et des cinétiques de ces chemins cohérents avec les résultats expérimentaux. Enfin, un essai de Traction-Compression cyclé sur une éprouvette de béton entaillée est simulé. Les mécanismes de refermeture de fissure et l’effet unilatéral sont décrits de manière satisfaisante.
... In view of this, different triaxial compression tests [6][7][8][9][10] have been performed to study the mechanical behaviour of concrete under a wide range of confining pressures and water contents. One observes that compressive/tensile strength of concrete decreases with increasing water content while volumetric stiffness of concrete increases with water content. ...
The present paper focuses on the hydro-mechanical behaviour of concrete under high confining pressures. By using the poromechanics approach, an elastoplastic model is adopted to describe the mechanical behaviour of concrete under different saturation conditions and high confining pressures. A hydrostatic compression test with the measurement of interstitial pore pressure is firstly used to identify the model’s parameter. After that, three quasi-oedometric tests with different water contents are simulated. The obtained numerical results exhibit that the mechanical behaviour of concrete is strongly coupled with its hydraulic responses. For instance: the saturation kinetics is accelerated by the plastic deformation related to pore collapse and volumetric compaction. The numerical predictions and discussions can help engineers to enhance their understandings on the influence of interstitial pore pressure on the vulnerability of concrete structures subjected to near-field detonations or impacts.
