Two-scale 3D printed steel fiber reinforcements strategy for concrete structures

Fibre-reinforced concrete is crucial for civil and structural applications. This paper introduces a novel two-scale strategy that utilizes 3D concrete printing (3DCP) to produce reinforcement infills and control fibre orientation for cementitious composite. In comparison with traditional mold-casting methods, the proposed strategy is proven to improve the flexural strength, toughness and stiffness of mortar beams by incorporating a 3DCP reinforcement infill. Furthermore, steel fiber reinforced 3DCP infills with three patterns: rectangle, triangle, and Hilbert curve, were fabricated and cast into mortar beams according to the proposed strategy. According to the results of four-point bending tests, arranging steel fibers in a rectangular pattern can improve the flexural strength and toughness by more than 100 % compared to randomly distributing steel fibers in the beams. Additionally, a triangular truss-like arrangement of steel fibers increased the flexural stiffness by 59 % compared to mold-cast beams with the same reinforcement ratio. While Micro-CT and Digital Image Correlation analysis demonstrate the performance of the composite beams can be further improved by reducing the interfacial porosities, the proposed two-scale strategy successfully demonstrates the ability to fabricate material-efficient structures with designed internal architectures.