Post-doctoral position proposal by CEA Saclay, France
News Category: 01. General - Association
Published: 2010-02-02 00:00:00
Post-doctoral position proposal (CEA Saclay, France):
Numerical estimation of the mechanical properties of the rebar/concrete interfaces subjected to corrosion
Corrosion of reinforcement rebars is one of the major causes of the premature degradation of reinforced concrete structures. Reinforcement corrosion begins when chemical and oxidant conditions are met for the depassivation of steel (carbonation and chloride ingress). Then, expansive corrosion products form, leading to a multi-layers pattern. In general, a "corrosion products layer" (CPL) and a "transformed medium" (TM) can be identified by microscopic analyses between metal and concrete [1]. The CPL formation may induce internal microcracking at the rebar/concrete interface, which in turn may lead to spalling or to delamination of concrete.
In order to perform accurate simulations of the response of reinforced concrete structures subjected to corrosion, it is desirable to model correctly the behaviour of the rebar/concrete interfaces, and in particular the development of the corrosion products. While the behaviour of plain concrete and sound steel are generally well known, few is known about such interfaces in terms of growth kinetics and mechanical properties.
We propose in this study to investigate this aspect at the microscopic scale by means of finite element simulations performed on 3D reconstructed microstructures. Use will be made of X-ray microtomography and SEM micrography experimental results to generate the numerical samples representative of the rebar/concrete interfaces. These samples will be modelled as multi-layers assemblages, including a steel layer, both CPL and TM parts, and an intact cementitious material layer. The latter material might be obtained by an automatic generation procedure implemented in the CAD code Salome. This procedure allows to creating a geometry composed of particles of various shapes and sizes (which represent the main hydrated products of the cementitious material, the porosity and the remaining anhydrous) distributed in a matrix [2]. Potential microcracks which may be detected experimentally, especially in the CPL, could also be modelled and incorporated in the geometry. In practice, the whole geometry of the assemblages will be created in Salome. Unstructured meshes with tetrahedral elements mapping the geometry will then be constructed by means of specialized meshing softwares. The transversely isotropic macroscopic mechanical properties of the microstructures will be obtained numerically with the FE code Cast3M developed at CEA, leading to the identification of the specific interface properties. The effects of different classical boundary conditions (i.e. static and kinematic homogeneous, mixed and periodic) applied to the samples boundaries will be examined. Likewise, various configurations (size and shape of the different layers and particles, microcracks) will be investigated to identify the major factors and evaluate their respective influence on the overall mechanical properties.
Contact:
Benoît Bary, CEA, Laboratory of Study of Concrete and Clay Behaviour Studies (LECBA)
Bâtiment 158, 91191 Saclay, France
benoit.bary@cea.fr
Phone: (33) 1 69 08 23 83
Expected salary: 2300 euros per month.
[1] W.J. Chitty, P. Dillmann, V. L’Hostis, C. Lombard, Long term corrosion resistance of metallic reinforcements in concretes - A study of corrosion mechanisms based on archaeological artefacts, Corrosion Science, Vol. 47 (6), pp. 1555-1581, 2005.
[2] B. Bary, M. Ben Haha, E. Adam, P. Montarnal, Numerical and analytical effective elastic properties of degraded cement pastes, Cement and Concrete Research. 39(10) 902-912, 2009.