Influence of Interface Zone Behaviour in Reinforced Concrete Under Tension Loading: An Analysis Based on Modelling and Digital Image Correlation

WOS:000380573600012International audienceThe problem of durability in reinforced concrete structures is a major case of concern nowadays. The problem of leakage due to cracking phenomena in critical structures such as nuclear power plants is specifically significant. In these structures, the number of cracks, their distribution and opening are needed to predict leakage possibilities. These variables depend on both the behaviour law of concrete and the behaviour law of steel-concrete interface. This article intends to compare experimental and modelling results focusing on interface zone between concrete and steel reinforcement. The first step consists in performing tests to capture behaviour of reinforced concrete prismatic elements subjected to pure tension. Crack opening along these structures is investigated by using digital image correlation (DIC), which allows the observation of crack propagation during loading. Next, the tension test of reinforced concrete is modelled in two different ways. Firstly, the connection zone between concrete and steel bar is assumed to be perfect (none-sliding connection). Then, a hypothesis of interface zone model between these two materials which allows plastic sliding [1], is considered. An orthotropic model of concrete based on plasticity and damage theories is used for this modelling. The model is able to predict crack opening and manage its reclosure [2]. Finally, results of the test are compared to the both modelling. A discussion concerning the need of interface model finishes this paper

Influence of Interface Zone Behaviour in Reinforced Concrete Under Tension Loading: An Analysis Based on Modelling and Digital Image Correlation

WOS:000380573600012International audienceThe problem of durability in reinforced concrete structures is a major case of concern nowadays. The problem of leakage due to cracking phenomena in critical structures such as nuclear power plants is specifically significant. In these structures, the number of cracks, their distribution and opening are needed to predict leakage possibilities. These variables depend on both the behaviour law of concrete and the behaviour law of steel-concrete interface. This article intends to compare experimental and modelling results focusing on interface zone between concrete and steel reinforcement. The first step consists in performing tests to capture behaviour of reinforced concrete prismatic elements subjected to pure tension. Crack opening along these structures is investigated by using digital image correlation (DIC), which allows the observation of crack propagation during loading. Next, the tension test of reinforced concrete is modelled in two different ways. Firstly, the connection zone between concrete and steel bar is assumed to be perfect (none-sliding connection). Then, a hypothesis of interface zone model between these two materials which allows plastic sliding [1], is considered. An orthotropic model of concrete based on plasticity and damage theories is used for this modelling. The model is able to predict crack opening and manage its reclosure [2]. Finally, results of the test are compared to the both modelling. A discussion concerning the need of interface model finishes this paper

Finite element modelling of permeability in brittle materials cracked in tension

WOS:000400227500007International audienceCracking in structures significantly affects their durability, water transfer and ultimately their safety. This structural disorder provides a preferential path for the penetration of fluids and contributes significantly to the deterioration of the material. In this work, a macroscopic model intended to predict the change of permeability with respect to cracking is proposed. The development reported here is implemented within an orthotropic continuum damage model able to calculate crack openings. The proposed model assumes an initially isotropic permeability tensor, which becomes anisotropic with damage. The objectivity of the hydraulic response toward the finite element mesh is ensured by considering the crack localization problem when building the permeability tensor. Finally, the model is used to simulate cracking and permeability variations on virtual and real structures. The simulation results are compared with experimental water flow rate measurements through a real reinforced concrete element subjected to tensile loading as found in the literature. (C) 2016 Elsevier Ltd. All rights reserved

Poromechanical consolidation and basic creep interactions around tunnel excavation

WOS:000400223000007International audienceIn drained compression tests, saturated specimens of claystone, collected by ANDRA (the French agency in charge of the management of radioactive waste disposal) from samples taken at 500 m depth, exhibit a visco-elasto-plastic behaviour and are also susceptible to damage. This viscous behaviour includes the viscosity of both the skeleton and the water. In existing models, the creep phenomena are attributed to the water permeability, to the skeleton visco-plasticity or sometimes to both. Using Biot's theory, the development reported here assumes a damageable visco-elasto-plastic argillite skeleton saturated by water. This model was used to simulate an excavation from ANDRA's underground laboratory (located in Sure, France), where increasing permeability with respect to crack opening was considered using Poiseuille's law. The proposed application explains how both viscous phenomena combine at each step of the calculation. Just after the excavation, water overpressure decreases near the gallery, approaching zero due to the damage, and thus increases permeability. The viscosity is then controlled by the solid skeleton creep rate. Later, the redistribution of hydraulic pressure becomes more important and permeability again plays a major role

Relative Contributions of Solid Skeleton Visco-Plasticity and Water Viscosity to the Poro-Mechanics Behavior of Callovo-Oxfordian Claystone

WOS:000345240600126International audienceThe Callovo-Oxfordian claystone is a saturated porous medium. Its transfer properties, including its low permeability [16] make it an interesting candidate for underground radioactive waste disposal. The drained tests performed on the claystone, collected by ANDRA(1) from samples at 500 meters depth [16, 9], exhibits a damageable visco-elasto-plastic behavior. This viscous behavior includes both the viscosity of the skeleton and the water. In existing models [5, 6, 11, 1], the creep phenomena are attributed either to the water permeability, to the skeleton visco-plasticity or sometimes both [13]. In a first step, a simplified analysis is proposed to understand the contribution of each phenomenon with respect to the consolidation time. This study indicates that the apparent characteristic time is the sum of those related to the skeleton and water permeability. To handle both non-linear and viscous phenomena, the damage law [15], coupled with the basic creep model [14] is used to characterize the solid skeleton of the claystone. The fluid behavior is integrated with the poro-mechanical model [7] implemented in the finite element code CAST3M [4]. The proposed model (visco-elastic damageable skeleton + saturating fluid) is used to simulate an excavation from the ANDRA underground laboratory (located in Bure-France). This application allows the understanding of how both viscous phenomena combine at each step of the calculation. Just after the excavation, water overpressure decreases near the gallery approaching zero due to the damage and then increases the permeability. The viscosity is then controlled by the solid skeleton creep rates. Later, the redistribution of hydraulic pressure is of more importance and permeability again plays a major role

Durability of dry-mix shotcrete using supplementary cementitious materials

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Effect of cement type on metakaolin efficiency

WOS:000340304500007International audienceIt is acknowledged in the literature that the performance of supplementary cementing materials such as fly ash or silica fume often depends on the characteristics of the cement used. This work aims to show that this dependence also concerns metakaolin. Compressive strength tests were carried out between 2 days and 2 years using one flash metakaolin and a panel of 11 cements having a wide range of characteristics. At 28 days of age, the difference in terms of strength activity index could reach 0.4 between the most and the least efficient cements. The hydration of MK pastes followed by XRD and thermal analysis showed that the pozzolanic reaction involving MM was postponed with low-C(3)A cements, as characterized by a delay of portlandite consumption and stratlingite formation. Several mechanisms are reviewed and discussed with the aim of explaining the role of cement in the development of the pozzolanic activity of MM. (C) 2014 Elsevier Ltd. All rights reserved

Numerical modelling of diaphragm wall construction

International audienceAbstract Diaphragm walls are rectangular shaped cast in place deep foundations. There are two critical phenomena occurring, according to which the final quality can be affected: bentonite suspension exfiltration and concrete placement. Some imperfections seem to appear recurrently on the surface of the final wall. The defects are known as shadowing pathologies. The main reasons can be attributed to the dual effect of exfiltration mechanisms and kinematics of concrete flow. The objective of this study is developing a numerical tool to prevent the appearance of shadowing pathologies by visualizing the concrete flow in the presence of a bentonite suspension. This paper presents the results obtained from 2D and 3D models of diaphragm wall construction using COMSOL Multiphysics. The CFD model helped in solving a multifluid and particularly a two‐phase flow. The 2D modeling has considered a fresh slurry and an exfiltrated (or polluted) suspension neighboring soil and followed concrete flow with two rheological behaviors in two reinforcement configurations. Then, 3D simulations were compared to actual experimentation results, which were undertaken to construct diaphragm walls in the laboratory. By comparing the results of the simulations to the experimental outcomes, it has been possible to validate the model. The resulting simulations could clearly explain the occurrence of the pathology where the flow pattern and volume fraction of the fluid flow were determined. From the results obtained, it can be conducted that a compliant concrete mix but at the lower limit for the consistency recommendations, leads to pathologies, just like a polluted slurry

Orthotropic damage coupled with localized crack reclosure processing Part II: Applications

WOS:000316092200011International audienceThis paper is concerned with the application of the orthotropic damage model described in the accompanying paper (Part I). The part I of the paper deals with several theoretical cases illustrating model's abilities to treat unilateral behaviour aspect, anisotropic loading and non radial loading pass. The second part illustrates the model's capabilities to simulate traditional laboratory tests using 3D FEM which include three points bending tests of notched beams, and examples which involve curved crack propagation, strongly anisotropic loading, and multiple cracks propagation in reinforced concrete beams. (C) 2012 Elsevier Ltd. All rights reserved

Orthotropic damage coupled with localized crack reclosure processing. Part I: Constitutive laws

WOS:000316092200010International audienceThe original model proposed present many advantages for applications which require cracks opening and reclosure management. It is easy to implement in most of the finite element codes based on a displacement formulation. It uses only measurable input data, like elasticity coefficients, tensile and compressive strengths, fracture energies and strains at the peak of the uni-axial stress-strain experimental curves. It supplies the crack opening perpendicular to the localized cracks directly, which can be plotted on the mesh. The orthotropic damage formulation on which it is based allows crack energy dissipation to be realistically verified and consequently ensures the objectivity of the FEM analysis toward the mesh size. Unilateral behavior and hysteretic dissipation due to crack re-closing phenomena are also considered in this framework. The latter aspect not only realistically predicts behavior during cyclic loading but, overall, provides a thermodynamic free energy form that can be generalized to treat quasi-unilateral aspects in various brittle materials concerned by crack re-closure problems. (C) 2012 Elsevier Ltd. All rights reserved