Abstract
The fracture toughness for the interfacial zone between a steel fiber and cementitious matrix was experimentally obtained by applying a compliance method to the single fiber pull-out test. Effects of the addition of silica fume and sand grains, and water: cement ratio on the fracture toughness were discussed relating them to characteristics of the fracture process revealed by the fluorescence microscope. Interfacial fractures under the pull-out loading were not a simple shear failure along the real interface. Local failures of the extended regions around a steel fiber were accompanied in the fracture process. The decrease in fracture toughness due to the addition of silica fume can be related to less microcracking in the interfacial zone and less tortuous extension of the interfacial cracks. In order to increase the fracture toughness for the interfacial zone, a small amount of carbon fiber was incorporated into the matrix. The addition of short carbon fibers was effective to improve the fracture toughness and the frictional stress in the interfacial zone. Steel fiber reinforced mortar with the matrix containing silica fume and short carbon fibers exhibited greater M. O. R. and toughness.
