A novel in-process rebar integration method for 3D printing reinforced concrete beams and performance evaluation

3D concrete printing technology (3DCP) offers unprecedented automation and customisation efficiencies for the construction industry, but the limitation of in-process reinforcement integration hinders its application scenarios and development. This study proposes an assembled reinforcement cage (ASC) system that innovatively decomposes conventional stirrups into mechanically interlocking segments with mortise-and-tenon connections, eliminating the fundamental conflict between layer-by-layer printing and cross-layer reinforcement requirements. Spatial reinforcement integration in 3D-printed concrete with coarse aggregate (3DPCA) beams was achieved using ASC, which leveraged the wider strips and longer travel distances of 3DPCA. Experimental tests and numerical simulations were conducted on four beam configurations. Results show that the ASC-reinforced 3D-printed beam outperformed the 3D-printed beam without stirrups, achieving a 127% improvement in first cracking load and a 20% increase in peak load, attaining 86% and 93% of the conventional beam and ASC-reinforced cast beam peak loads, respectively. Strain analyses confirmed effective load transfer and synchronised deformation between the 3D-printed concrete and ASC reinforcement through joint mechanical engagement. Finite element modelling incorporating the interlayer traction-separation law accurately predicted different failure mechanisms for 3D-printed beams and cast beams, with an accuracy of 94.9-98.6% for peak loads. The ASC system offers a transformative solution for automated, structurally sound 3DCP.