Flexural performance of concrete beams via 3D printing stay-in-place formwork followed by casting of normal concrete

In traditional mold-casting for concrete, the process of assembling and demolding formwork is both costly and time-intensive, limiting the design possibilities of complicated shaped and composite applications. Autonomous or semi-autonomous 3D concrete printing presents an innovative solution, allowing for the customization of intricate formwork shapes and facilitating the creation of composite structures. This study develops and manufactures a novel concrete beam that incorporates 3D-printed (3DP) ultra-high performance strain-hardening cementitious composites (UHP-SHCC) U-shaped jackets used as stay-in-place formwork, with normal concrete (NC) as filled concrete. To evaluate the flexural performance of the proposed beam, composite beams with cast-in-place formwork and post-cast NC, fully cast NC beams and fully cast UHP-SHCC beams are also tested. The flexural performance of these beams is assessed through four-point bending tests, including failure modes, load–displacement response, and cracking behavior. Results indicate that concrete beams utilizing 3DP UHP-SHCC stay-in-place formwork demonstrate superior flexural performance, characterized by deflection-hardening behavior, outperforming the other tested configurations.