Variation of fracture energy dissipation along evolving fracture process zones in concrete

This paper examines the fracture energy properties over ligament length for crack propagation process accompanied by fracture process zone (FPZ) advancement. Local fracture energy as well as its average value along the crack path is investigated by considering the influence of specimen boundaries on the development of FPZ. To address the specimen boundary affected region over which local fracture energy generally spreads in a non-uniform manner, two concepts are introduced: Back boundary affected length and overall boundary affected length. Tests were conducted on wedge splitting concrete specimens to identify the variation of fracture energy dissipation when FPZ evolves toward the specimen back surface. Results included here reveal that the back boundary affected length is decreasing approximately in a linear way along with crack evolution. The overall boundary affected length, however, proves to be increasing at early stages of crack growth and then decreasing in a way similar to the back boundary affected length. Local fracture energy over crack extension decreases before FPZ gains its full development. For the case of a full-developed FPZ, it can be described by two different forms: one is in the form of a horizontal line, the other part shows to be decreasing but with a constant average value. The average value of local fracture energy, however, is predicted to increase along with the evolution of FPZ.