Effect of casting geometry on distributions of segmented steel fibers in ultra-high performance fiber-reinforced concrete

In this study, influence of flow distance and casting direction to properties of steel fibers in ultra-high-performance fiber-reinforced concrete (UHPFRC) was investigated using 3D data on the fibers that accurately obtained through multiple microcomputed tomography (micro-CT) scans and image processing. 3D images of bundled fibers were separated to individual strands by means of a 3D watershed algorithm. The variation in fiber properties according to distance from the casting point and the casting direction was quantitatively analyzed. The results indicated that many fibers were distributed at the casting position for the horizontally casted specimen. The fibers tended to move along the major upward flow of the UHPFRC mixture, which in turn, gradually inclined upward and oriented horizontally in concentric circles. However, different major flow patterns and fiber orientations appeared depending on the casting direction due to the wall effects induced by formwork boundaries. It was also found that fiber content is the dominant factor affecting the 3D dispersion of fibers.