Fiber Orientation Control in Spray-Based 3D Printed Steel Fiber Reinforced Concrete (2025-11)¶

This study investigates the effects of steel fiber contents (0–3.0 vol% at 0.5 vol% increments) on fiber orientation control and mechanical enhancement in spray-based 3D (S-3D) printed steel fiber reinforced concrete. Fiber orientation distribution, orientation ratio, pore structure, and fiber–matrix interfacial morphology are characterized using X-ray computed tomography (X-CT) and scanning electron microscopy (SEM). Based on flexural stress field distribution of beam, an optimized S-3D printing path is designed to maximize fiber alignment effect. The test results show that the S-3D printing process effectively orients steel fibers in printed concrete, achieving a maximum orientation ratio of 65.88 % at 2 vol% fiber content (P2). Meanwhile, this process effectively optimizes the microstructure of the concrete. As revealed by SEM observations, the porosity is reduced to as low as 1.41 %, and the fibers exhibit strong interfacial bonding with the matrix. The fiber orientation effect can effectively enhance the strength and toughness of concrete. In the Y direction, the 28-day compressive and flexural strengths of printed P2 maximumly reach 87.5 MPa and 22.0 MPa, representing increasement of 16.48 % and 10.78 % over cast specimen with identical fiber content (C0), and 23.15 % and 87.23 % than that of printed fiber-free specimen (P0), respectively. The optimized printing path enhances fiber alignment, yielding 49.34 % higher flexural strength and 14.12 % greater deformation capacity compared to cast beam. These findings demonstrate that S-3D printing facilitates precise fiber orientation control, unlocking the high-strength and -toughness potential of steel fibers and providing a viable approach for structural-scale concrete for additive manufacturing.