ABSTRACT
Ultra-High Performance Concrete (UHPC) has ultra-high tensile strength and toughness compared to normal concrete (NC), this advantage often benefits from the higher volume content of steel fibers. Some studies reported that the fibers are randomly distributed in the UHPC matrix, and the effectiveness of fibers is less than 40%. Increasing the fiber content has been proven to be an effective means to enhance the properties of materials, but the problems such as fiber agglomeration and local defects of materials will increase significantly. To solve the above problems, the aligned steel fiber UHPC (ASF-UHPC) was successfully developed by the theory of electromagnetism. The steel fibers aligned in UHPC matrix can optimize the fiber utilization efficiency, improve the material performance and reduce the unit cost. Meanwhile, a series of reinforced ASF-UHPC beams were cast by this method, and the bending test was conducted to study its flexural behavior, failure patterns, and load-deflection relationship. The relative fiber orientation in the reinforced beams was studied by CT 3D image technology, and the difference in flexural properties between ASF-UHPC beam and normal UHPC (N-UHPC) beam was analyzed from the point of view of the orientation of fibers. The research results show that the homogeneous magnetic field can optimize the fiber orientation in reinforced UHPC beams, and the fibers are parallel to the beam, which can improve the flexural load capacity. For instance, when the volumetric ratio of steel fibers is 2%, the flexural capacity of ASF-UHPC beam can be improved by about 24% at a low rebar ratio (0.016). Through the parametric analysis of different fiber volumetric ratios and fiber orientation, the enhancement efficiency of flexural capacity was studied, which provides reference value for improving the mechanical properties of UHPC material, reducing the cost of using UHPC and promoting carbon neutrality.
