Prediction Of The Elastic Modulus Of Concrete With Interfacial Cracks

At a mesoscopic level, concrete can be considered as a three-phase composite material, consisting of cement paste, aggregates and interfacial transition zone (ITZ). Therefore, the macroscopical mechanical properties of concrete is, to a large extent, dependent on the mechanical properties and volume fractions of the three phase constituents, and the interaction among them. It is generally acknowledged that, the ITZ is formed due to the wall effect of the aggregate surface on the distribution of cement particles. Compared with the cement paste and aggregates, the ITZ is the weakest link. The higher porosity, lower stiffness and lower strength of the ITZ make it easy to form interfacial cracks when the deformation of concrete occurs for various reasons. Therefore, it is of theoretical and practical significance to study the effect of interfacial cracks on the elastic modulus of concrete for further understanding the macroscopical mechanical properties of concrete.The intention of the thesis is to study the elastic modulus of concrete with elliptical aggregates and the effect of interfacial cracks on the elastic modulus of concrete. First, based on the theory of stereology, elliptical aggregates are generated and distributed by computer simulation and the mesostructure of concrete is reproduced. Second, a modified lattice model is used to predict the elastic modulus of concrete with elliptical aggregates. The validity of the method is preliminarily verified with two sets of experimental data collected from the literature. Finally, a prediction method is developed for predicting the elastic modulus of concrete with interfacial cracks by introducing a interfacial crack. The effects of various key factors on the elastic modulus of concrete are evaluated in a quantitative manner. Numerical results show that the elastic modulus of concrete decreases with the increase of the crack size, but the decrease rates are different for parallel and uniformly oriented cracks. For a given crack size, the elastic modulus of concrete decreases with a decrease in included angle between the interfacial crack and the longitudinal axis. For parallel cracks, aggregate shape has a larger influence on the elastic modulus of concrete.