It is well known that fine and coarse aggregates play a vital role in the fracture of concrete. There is, however little quantitative information available in the literature on the effect of the volume fraction of the aggregates on the fracture properties of concrete. The main objective of this work is to gain a better understanding of this effect using appropriate experiment and a meso-mechanical approach. For this, several control mixes ranging from hardened cement paste (HCP) to normal concrete were prepared in which the aggregate grading, w/c ratio, and the maximum particle size of aggregate were kept constant, but the volume fraction of aggregate was varied from 0.0 (HCP) to 0.60 in steps of 0.15. The critical stress intensity factor of the hardened cement paste, for which linear elastic fracture mechanics (LEFM) is valid, was determined from centrally notched disc specimens. The effective stress intensity factors of fine mortar coarse mortar and concrete were then calculated from that of HCP using the appropriate toughening mechanism in meso-mechanical relations. The specific fracture energies, the macro-tensile strengths and the moduli of elasticity of fine mortar coarse mortar and concrete were also calculated from meso-mechanical relationships. From these, the ductility of the mixes was calculated in terms of the characteristic length. It is shown how the meso-mechanical modelling approach gives a clear qualitative and quantitative picture of how a brittle matrix (i.e. HCP) progressively transforms into a tougher stiffer and more ductile composite as the volume fraction of fine and coarse aggregates is increased without altering their grading.