Abstract
The aim of this thesis is to understand and characterize the local mechanisms of deformation involved in the failure of a concrete sample in compression test. Thus, it is a question of establishing a correlation between these local mechanisms and the macroscopic response of the material. Concrete is considered as a multiphase material associating cement paste, aggregates and interfacial transition zones (ITZ). Because of its multiphase character, the stress is locally multiaxial. Understanding local mechanisms of generated deformation is based on a numerical modeling. The construction of a representative elementary volume (REV) as close as possible to the experimentally tested material was a part of this thesis subject. Cohesive zone models are adopted to describe the mechanical behavior of the cement paste/aggregate interface and to simulate cracking in the paste. The identification of the parameters of these models is based on experimental tests carried out at the local scale (characterization of the cement paste/aggregate interface) and at the mesoscopic scale (characterization of the cement paste).This numerical modeling was then used to determine the parameters governing the initiation of damage and the strength. This sensitivity analysis was performed by a screening method. This work shows that the damage is strongly affected by the quality of the cement paste/aggregate interface. Depending to the interfacial stiffness, it is initiated at the interface or in the cement paste. The strength is related to the mode II cohesive stress of the cement paste.This model was then used to study the damage and failure mechanisms involved during the hardening of concrete. Finally, the influence of the aggregate fraction on the pre-peak and post-peak behavior of concrete is discussed.