Characterizing rheology of fresh short fiber reinforced cementitious composite through capillary extrusion

The rheology behavior of fresh short fiber reinforced cementitious composite (SFRCC) for extrusion purpose was investigated through capillary extrusion. It was found that the classical capillary theory for single-phase fluid was not appropriate to interpret the flow behavior of fresh SFRCC due to the large pressure loss occurring at the capillary entrance and the significant slip effect happening in the capillaries. By using a set of capillaries with the same diameter but different lengths, the true shear stress was derived on the basis of Bagley's end correction while the slip effect was calibrated through a series of capillary extrusion tests with different capillary diameters. It was found that the slip velocity could be determined by the Jastrzebski model. Further studies showed that the intrinsic rheology behavior of fresh SFRCC could be modeled by the Herschel-Bulkley equation and the associated parameters could be determined through the experimental and the data interpretation method described in this paper. The fresh SFRCC flow in capillary extrusion was dominated by slip, and the velocity profile could be determined through a superposition of an internal shear flow with a plug flow. The slip layer thickness developed in the capillaries was also estimated based on the calibrated theory and experimental data.