In-process reinforcing method: dual 3D printing procedure for ultra-high performance concrete reinforced cementitious composites

The general application of 3D printed concrete (3DP-C) in practical engineering is significantly hindered by the lack of adequate reinforcement procedures, which is an intrinsic limitation of the 3D printing process. To address this limitation, this study proposes an in-process dual-printing reinforcement method, which concurrently and continuously prints ultra-high performance concrete (UHPC) and ordinary 3DP-C. The UHPC, as an integral part of the printed structure, serves as reinforcement for the overall concrete composite. Printing equipment for these dual concrete materials is developed to realize the coordination of the dual-material deposition process. Significant improvement of mechanical properties of 3D printing UHPC (3DP-UHPC) reinforced 3DP-C, which is then abbreviated as 3DP-UHPCRC, is demonstrated through four points bending tests of thin plate specimens. In comparison to plain 3DP-C, the reinforced concrete possesses an 160.5% increase in ultimate bending strength as well as a brittle to ductile bending failure mode transition, thus demonstrating the effectiveness of the proposed reinforcement method.