CRACK-PROPAGATION IN CONCRETE COMPOSITES INFLUENCED BY INTERFACE FRACTURE PARAMETERS

The mechanical behavior of concrete composites is influenced by the ch aracteristics of mortar-aggregate interfaces. Initiation and propagati on of cracks at the interface or penetration of cracks into the aggreg ate can greatly influence the global behavior of the material. In the interfacial regions of concrete composites the crack path criterion wi ll involve relative magnitudes of the fracture toughnesses between the interface and the constituent materials. This study investigates frac ture 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 mis match between the mortar and the aggregate and the ratios of the inter face fracture toughness to the fracture toughness of the aggregate and the mortar. Numerical and physical model tests were performed to stud y the influence of these variables on the global load-deformation beha vior of composite beams. Physical beam models consisting of circular a ggregate inclusions in mortar matrices were tested in three-point bend ing. An analysis capability is developed for cracking in the composite incorporating transgranular or interfacial fracture scenarios using f inite element simulations performed with the material fracture propert ies. The simulation is of a cohesive force type that allows parametric variation of fracture parameters to study influences on load-deformat ion performance of the composite. Results of the simulation are used t o quantify the effect of different interfacial properties on the Fract ure and load-deformation behavior of the specimens. The results of bot h the experimental and analytical model studies show that ductility im proves when cracks propagate through mortar-aggregate interfaces and a lso 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-performan ce cementitious materials. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.