Enhancing the flexural performance of concrete beams with 3D-printed UHP-SHCC permanent formwork via graded fiber volume fraction

Conventional concrete structures often rely on labor-intensive and wasteful formwork systems. In contrast, 3D concrete printing (3DCP) technology offers a more efficient alternative for fabricating complex-shaped permanent formwork. This study fabricates innovative composite beams using 3D-printed ultra-high-performance strain-hardening cementitious composites (UHP-SHCC) as permanent formwork, followed by casting infill materials. The spatially tailored fiber dosage distribution in the 3D-printed UHP-SHCC permanent formwork enables the performance optimization of the composite beam. The flexural behavior of three such formed composite beams is evaluated using four-point bending tests. A reference beam with homogeneous fiber distribution in the UHP-SHCC formwork is also tested for comparison. The failure mode, overall load–displacement response, and cracking performance of four beams are comprehensively characterized and compared. The results reveal that employing graded fiber dosages in UHP-SHCC formwork enhances fiber efficiency and structural performance while reducing fiber usage and material costs. The use of 3D-printed UHP-SHCC formwork with graded fiber distribution, despite using 25% less fibers and reducing the material cost by 12.8%, leads to a 65.6% increase in strength and over 50% increase in energy absorption, or a 77.4% increase in ultimate displacement with comparable peak load to the reference beam with homogeneous fiber distribution. © 2024 Elsevier Ltd