Compression triaxial behavior of concrete: the role of the mesostructure by analysis of X-ray tomographic images

This paper is intended to assess the mesostructural damage mechanisms of concrete under hydrostatic and triaxial loadings. Such a study is possible thanks to two state-of-the-art laboratory instruments: a high-pressure triaxial press, and an X-ray computed tomography instrument. The laboratory protocol consists of scanning the concrete prior to the initial loading and after each cycle. An analysis of the resulting images indicates that under high hydrostatic loading, significant damage is visible in cement paste at the mesoscopic scale. For two triaxial tests conducted at 50 and 650 MPa of confining pressure, results reveal major differences in both damage and failure mechanisms. At the lower pressure, shear loading creates a localised failure mechanism characterised by sliding on an inclined plane, whereas at the higher pressure, the strain and damage mode are much more homogeneous with a failure localisation after unloading. Cet article a pour objectif d’estimer les mécanismes d’endommagement du béton présents à l’échelle mésoscopique sous chargements hydrostatique et triaxial. Une telle étude est possible grâce à deux instruments de laboratoire: une presse triaxiale de grande capacité, et un tomographe à rayons X. Le protocole de réalisation des essais consiste à scanner le béton à l’état vierge et après chaque cycle. L’analyse des images obtenues indique que sous fort chargement hydrostatique, l’endommagement est visible dans la pâte de ciment à l’échelle mésoscopique. Pour deux essais triaxiaux, réalisés à 50 et 650 MPa de pression de confinement, les résultats montrent des mécanismes d’endommagement et de rupture très différents. À basse pression, le cisaillement provoque un mécanisme de rupture qui apparait sous la forme d’un plan de glissement incliné. À forte pression, la déformation et le mode d’endommagement sont beaucoup plus homogènes avec néanmoins une localisation de la rupture lors de la décharge.

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