MICROMECHANICAL MODELING OF SOFTENING BEHAVIOR IN STEEL FIBER-REINFORCED CEMENTITIOUS COMPOSITES

The fracture of cementitious materials is governed by its softening be havior. When steel fibers are incorporated into concrete to improve it s toughness, the softening behavior can be predicted in terms of the c omposite micro-parameters including the properties of fiber, matrix an d interface as well as fiber size, length, distribution and volume fra ction. In this paper, the bridging force provided by a steel fiber at any arbitrary angle to the crack is first modeled in terms of the micr o-parameters. For a given fiber distribution, the averaged crack bridg ing force is then derived and employed to obtain the composite softeni ng behavior. The model is verified at both the microscopic and macrosc opic levels with experimental results from the fiber pull-out test and the four-point beam bending test. With the model, numerical simulatio ns are carried out to study the effect of various parameters on the te nsile softening behavior. These simulations can facilitate the choice of micro-parameters for the most cost-effective material design. (C) 1 998 Published by Elsevier Science Ltd. All rights reserved.