Two-Dimensional Magnetic Orientation of Steel Fibers in Large Slab Elements Made of HPFRC Using an Industrial Robot

Steel fiber-reinforced concrete (SFRC) can exhibit markedly improved mechanical performance when the fibers are preferentially aligned along the principal tensile stress directions. One method of aligning steel fibers is using magnetic methods. However, most existing magnetic alignment techniques rely on solenoids and are restricted to one-dimensional alignment and relatively small specimen sizes. This paper presents a novel planar magnetic orientation device capable of producing arbitrary two-dimensional fiber layouts and demonstrates its applicability from laboratory-scale proof-of-concept tests to large high-performance fiber-reinforced concrete (HPFRC) structural elements. The concept is first verified on transparent ultrasound gel specimens, where image analysis confirms fiber orientation in the prescribed angles. The method is then applied to small prismatic HPFRC specimens (40 mm × 40 mm × 160 mm) with fiber contents of 0.5%, 1.0%, and 1.5%, exposed to different magnetic field intensities (80 mT-140 mT). Flexural tests show increases in average flexural strength compared to non-oriented reference specimens, with 100 mT providing the most efficient alignment for the investigated mixture. A non-destructive electromagnetic method based on the measurement of the quality factor Q of a coil correlates well with flexural strength. Finally, the device is integrated with an industrial robot and used to orient fibers in large HPFRC slabs (1000 mm × 410 mm), achieving an average increase in flexural tensile strength of about 64% relative to non-oriented slabs. The results demonstrate that planar magnetic orientation is a promising approach for tailoring fiber layouts in SFRC structural elements and for enabling automated, programmable manufacturing.