Fracture surface-based toughness modeling of cement-based materials

One of the major principles of fracture mechanics of brittle materials is that the energy consumed in extending a crack through the material is related to the newly created surfaces, or surface energy. For ductile materials such as steel, fracture is dominated by plastic mechanisms, and surface energy is a small component. For quasi-brittle materials such as concrete, "pseudo-ductile" behavior results from the heterogeneous microstructure that causes cracks to deflect through a complex assembly of brittle phases and porosity. This study explores the hypothesis that the rough surfaces created by the fracture process can be used to characterize the fracture behavior of quasi-brittle materials. Several methods are used to measure the geometry of the fracture surface, along with subsurface cracking. Novel specimen preparation methods and measurement techniques were employed to assess fractured specimens. Mechanical tests were performed to measure fracture toughness. A model is proposed to link fracture surface parameters to fracture toughness.