Relation of fracture process zone to tension softening behavior of concrete has been studied using fracture energy tests for various concrete, focusing on change in properties of the internal structure of concrete. Six series of test for the following materials were performed; high strength concretes, normal concretes, concretes with different maximal particle size, concretes in seven different ages, fiber reinforced mortars, and frozen mortars.
The parameters of bi-linear tension softening model for the materials were determined based on a data fit technique to discuss the relation between the tension softening properties and the factors which affect the internal structures of concrete. The results indicate that the behavior in the beginning of descending branch of the tension softening diagram corresponds to micro crack localization and extension and that successive behavior in the tail of tension softening is attributed to the bridging mechanism at the interface between the matrix and aggregates.