Influence of Reinforcing Index on Rheology of Fiber-Reinforced Mortar

The relationships between the reinforcing index (RI: the product of volume fraction and length-to-diameter ratio of fibers) and rheological parameters (hysteresis loop area, yield stress, plastic viscosity, flow spread, and flow rate) of a single type of fiber-reinforced cementitious composites (SgFRCCs) and hybrid fiber-reinforced cementitious composites (HyFRCCs) with steel, polyvinyl alcohol (PVA) fibers, and calcium carbonate (CaCO3) whiskers, were systematically studied for the first time. After shearing action, short whiskers between cement particles prevented the cement particles from coming close to each other, leading to more irreversible broken structures in the entire rheological test process, which means higher hysteresis loop areas than those of longer fibers. The new hybrid fiber system decreased the yield stress and plastic viscosity to a certain extent, as a result of the "grading effect" of hybrid fibers and whiskers. Based on the theoretical framework of random loose packing, the critical RI values for single PVA fibers and hybrid fibers were approximately 1.0 and 2.0, respectively, which supports this theoretical framework and the effect of critical RI values in fiber-reinforced mortar. The influence of the RI on the characteristics of fresh HyFRCCs can be quantified well into a multivariate linear relationship. Moreover, these findings can be used to optimize fiber mixtures in practical project applications.