Studies on Fracture and Fatigue Behavior of Cementitious Materials- Effects of Interfacial Transition Zone, Microcracking and Aggregate Bridging

Abstract

The microstructure of concrete contains random features over a wide range of length scales in which each length scale possess a new random composite. The influence of individual material constituents at different scales and their mutual interactions are responsible for the formation of fracture process zone (FPZ). The presence of the FPZ and the various toughening mechanism occurring in it, influences the fatigue and fracture behavior of concrete which also gets influenced by the geometry, spacial distribution and material properties of individual material constituents and their mutual interactions. Hence, in order to study the influence of interfacial transition zone, microcrack and aggregate bridging on the fracture and fatigue behavior of concrete, a multiscale analysis becomes necessary. This study aims at developing a linearized model which helps in understanding the fracture and fatigue behavior of cementitious materials by considering the predominant fracture process zone (FPZ) mechanisms such as microcracking and aggregate bridging. This is achieved by quantifying the critical microcrack length and the bridging resistance offered by the aggregates. Further, the moment carrying capacity of a cracked concrete beam is determined by considering the effect of aggregate bridging. A modified stress intensity factor (SIF) is derived based on linear elastic fracture mechanics (LEFM) approach by considering the material behavior at different scales through a multiscale approach. The model predicts the entire crack growth curve for plain concrete by considering these process zone mechanisms. Furthermore, the fracture and fatigue response of concrete is studied through the development of analytical models which include the properties of the mix constituents using the multiscale based SIF. The effect of the interfacial transition zone, microcracks and resistance offered through aggregate bridging on the resistance to crack initiation and propagation are studied. A fatigue crack growth law is proposed using the concepts of dimensional analysis and self-similarity. Through sensitivity analyses, the influence of different parameters on the overall fracture and fatigue behavior are studied. In addition, studies related to concrete-concrete bi-material interfaces are conducted in order to understand the influence of repair materials on the service life of damaged concrete structures when subjected to fatigue loading. An analytical model is proposed in this study to predict the crack growth curve using the concepts of dimensional analysis and self-similarity in conjunction with the human population growth model. It is seen that a repair done with a patch having similar elastic properties as those of the parent concrete will have a larger fatigue life.