Fracture process zone has a strong effect on fracture energy particularly for concretes with coarse aggregates. In order to demonstrate this effect, four groups of concrete mixtures with various aggregate volume fractions were designed. Three point bending tests were applied on beam specimens with a single size but different notch size to obtain the boundary effect model based fracture energy. The results were evaluated to determine the effect of both aggregate volume fraction and notch size on fracture energy of concretes. In addition, meso-mechanical relations based on toughening mechanisms were employed in determining the fracture energy of concrete. The fracture energies obtained from the meso-mechanical approach and the boundary effect model were compared and found to be in good agreement. (C) 2011 Elsevier Ltd. All rights reserved.