When massive concrete structures (high-rise buildings, tunnels, dams, nuclear power plants, bridges, protection structures, ..) are subjected to extreme loadings (aircraft shocks, rock falls, near-field detonations, ballistic impacts, ..), the material undergoes triaxial compression loading at a high confinement. In order to reproduce high stress levels with well-controlled loading paths, static triaxial tests are carried out on concrete samples by mean of a very high-capacity triaxial press. It is a well-known fact that the cement paste volume and the coarse aggregate size are two important parameters of concrete formulation. This article focuses on identifying the effect of coarse aggregate size and cement paste volume on concrete behavior under high triaxial compression. This article shows that at low confinement, the concrete strength slightly increases as the coarse aggregate size increases. At high confinement, the coarse aggregate size has a slight influence on concrete deviatoric behavior and a significant influence on concrete strain limit-state. The higher the coarse aggregate size, the lower is the mean stress level corresponding to concrete strain limit-state. Furthermore, this article highlights that at low confinement, the concrete strength significantly increases with an increase in cement paste volume. Increasing confinement tends to reduce cement paste volume effect on concrete strength. At high confinement, contrary to what has been observed in unconfined compression, the cement paste volume has little effects on concrete deviatoric behavior. Otherwise, decreasing cement paste volume increases concrete deformation capacity. At very high confinement levels and at very high deviatoric stress levels, the axial tangent stiffness of concrete increases as the coarse aggregate size or the cement paste volume is reduced. © 2011 Elsevier Ltd. All rights reserved.