Crack propagation in concrete composites influenced by interface fracture parameters

The mechanical behavior of concrete composites is influenced by the characteristics of mortar-aggregate interfaces. Initiation and propagation of cracks at the interface or penetration of cracks into the aggregate can greatly influence the global behavior of the material. In the interfacial regions of concrete composites the crack path criterion will involve relative magnitudes of the fracture toughnesses between the interface and the constituent materials. This study investigates fracture of two-phase composites in terms of parameters that influence the cracking scenarios in the interfacial regions and affect the fracture behavior of the concrete. These parameters include elastic moduli mismatch between the mortar and the aggregate and the ratios of the interface fracture toughness to the fracture toughness of the aggregate and the mortar. Numerical and physical model tests were performed to study the influence of these variables on the global load-deformation behavior of composite beams. Physical beam models consisting of circular aggregate inclusions in mortar matrices were tested in three-point bending. An analysis capability is developed for cracking in the composite incorporating transgranular or interfacial fracture scenarios using finite element simulations performed with the material fracture properties. The simulation is of a cohesive force type that allows parametric variation of fracture parameters to study influences on load-deformation performance of the composite. Results of the simulation are used to quantify the effect of different interfacial properties on the Fracture and load-deformation behavior of the specimens. The results of both the experimental and analytical model studies show that ductility improves when cracks propagate through mortar-aggregate interfaces and also improves with rougher aggregate surfaces. This study advances the understanding of the role of interfaces in the global behavior of the cementitious composites and Furthers the development of high-performance cementitious materials. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.