Fracture energy has been used as a material parameter to describe the crack resistance of concrete. It is known, however, that the fracture energy depends on specimen size even if the mix proportion of concrete is the same. In this paper, the relation between the fracture properties of concrete and the micro structure, and the size effect are discussed. Three different mix proportions of concrete and three different specimen sizes are used, where the quality and the volume of coarse aggregates are kept constant. Furthermore, the applicabilities of 'size effect law' and 'two parameter fracture model' which have been noticed as potential approaches to predict the size effect of concrete structures, are discussed.
