International audienceThe aim of this study is to investigate and to simulate damage mechanisms of concrete under fire conditions. A micro-mechanical model has been developed by coupling the effective moduli approach with a finite element model based on the representation of the heterogeneous materials random microstructure. Numerical simulations have been carried out in order to analyze the effective behaviour of confined concrete samples subjected to high temperatures coupled to compressive loads and to localize damage on the microstructure scale. These simulations show that the 'transient thermal strain', noticed during experimental tests, is due to the thermal damage of concrete

This work aims at providing a multi-scale model to estimate the effective properties of hemp and lime concretes. The microstructures of such materials are characterized by a relatively high filling rate, platy orthotropic particles distributed on a wide range of spatial directions, and a high level of porosity at meso and micro scales. An iterative micromechanical modeling is here enhanced with some numerical features allowing to deal with the shape and orientation of the particles and with the resulting effective anisotropy of concretes. The model thus constructed is first put into practice to identify the properties of hemp shives and air-slaked lime for various compaction degrees. The results obtained are then used as input data to estimate the thermal and mechanical properties of both a collection of moderately compacted concretes, and a set of concretes with several compaction degrees. Simulations results are eventually confronted with experimental data from the literature.

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