Microcrack propagation and softening behavior of concrete materials

There exists a critical difference between pre-failure behavior and post-failure behavior of concrete materials. However, this difference is yet to be thoroughly understood. This is probably the reason why the modeling of softening behavior is not well-developed. The present study attempts to shed some light on this aspect. Based on the experimental evidence, the difference between the hardening and softening behaviors is first examined. The appearance of nonhomogeneous deformation after failure is pointed out. The cause of such difference is then investigated. To this end, microscopic events in concrete are focused. The present research touches on the subjects of microscopic observation, micromechanical approach, fracture mechanics of concrete and the effect of aggregate-mortar interaction. Through this study, the key factors that must be taken into consideration in a microcrack analysis of concrete are identified. Also, the possible account for nonhomogeneous deformation is discussed. The essential features of concrete mechanics are formulated. The new model for an opening-mode fracture is developed and a joint element is applied to simulate bond crack. The crack analysis of concrete-like composites is conducted. Attention is given to the influence of stress state in mortar matrix on the crack propagation. The implication of the numerical results is discussed. Finally, the crack analysis is performed for the composite material under tensile loading condition. The distinction between the behaviors of concrete in tensile and in compressive loadings can be explained by the results obtained in the present analysis