Preparing process and the mechanical properties of bi-directionally aligned steel-polypropylene fiber-reinforced cementitious composites

Aligned steel fiber-reinforced cementitious composites (ASFRC) exhibit exceptional tensile strength in the fiber-aligning direction. However, the mechanical properties of composites in the direction perpendicular to steel fiber are weakened owing to the anisotropy of ASFRC. This study proposes a bi-directionally aligned steel-polypropylene fiber-reinforced cementitious composites (BASPFRC) incorporating steel fibers and polypropylene fibers oriented perpendicularly to one another. The design principle and preparation process of BAFRC are presented, then its fiber orientation by X-ray CT and multidirectional tensile performance by Brazilian splitting test are subsequently evaluated. The study demonstrates that the integration of flow-induced alignment and magnetic field control is an effective method for preparing bidirectionally aligned fiber-reinforced concrete (BAFRC). It enables a high degree of fiber orientation, achieving orientation coefficients of 0.8 for both steel fibers and polypropylene fibers in their intended alignment directions. In the direction perpendicular to the aligned steel fibers, the splitting tensile strength of BASPFRC showed a slight decrease of 5% compared to randomly aligned fiber-reinforced concrete (AFRC). Conversely, in the parallel direction, the splitting tensile strength exhibited a substantial increase of 57%, indicating enhanced load-bearing capacity and reduced mechanical anisotropy. This study reveals that the mechanical performance of BASPFRC can be tuned by adjusting the content and orientation of fibers in both directions, providing a new insight into the controllable design of fiber-reinforced composites through microstructural orientation manipulation.