Rheology of fiber reinforced cementitious materials: classification and prediction

In this paper, the effect of rigid straight fibers on the yield stress of cementitious materials is studied. A simple model describing the contact network between rigid fibers inside the material is first derived from the physical phenomena involved in the case of spherical inclusions. As soon as this contact network becomes percolated, the yield stress of the mixture increases by several orders of magnitude. A prediction of the critical fiber amount leading to a very strong increase of the yield stress of any cement paste, mortar or concrete is then derived. A simple and helpful mix design criterion for Ultra High Performance Fiber Reinforced Concretes is finally proposed and applied to several mix proportions from literature.