This communication concerns the identification of the concrete behavior under extreme loading situations (near field detonation or ballistic impacts). In order to reproduce high stress levels with well-controlled loading paths, static tests have been carried out on concrete samples by mean of a very high-capacity triaxial press. The objective of this paper is to quantify the effect of composition of concrete (cement paste volume, aggregate size) on its behavior under static high triaxial loading. The experimental tests results confirm that under low confinement, the strength and the axial tangent stiffness of concrete increase significantly with cement paste volume increase and slightly with aggregate size increase. Under high confinement level as the cementitious matrix is not more cohesive, phenomenon observed in low confinement are reversed, the tangent stiffness of concrete decreases with the increase of cement paste volume or of aggregate size. © 2010 Taylor & Francis Group, London.