Effect of Cracking and Fracture Mechanics Aspects of Creep and Shrinkage Analysis
The nonuniformity of drying shrinkage and drying creep, as well as the stress redistributions due to nonuniform creep, typically cause distributed cracking and continuous fractures, which lead to ingress of corrosive agents into concrete and compromise durability. In this chapter, we present an analysis of these phenomena from the viewpoint of fracture mechanics. We explain the crack band model, which is a simple and effective way of avoiding spurious mesh sensitivity in finite element simulations. We analyze the role that cracking plays in drying creep. The creep and rate effects influence the crack propagation, which we describe in terms of the cohesive crack model. We also explain the origin of the rate effect in cohesive fracture, which lies in the fracture kinetics on the atomic scale. Further, we point out that cracking is also a partial cause of the irreversibility of shrinkage and creep, and causes nonlinear stress dependence of drying creep. Finally, we discuss material models combining damage and creep.