Mechanical properties of 3DPC-NC structural system based on wavy printing path

Concrete 3D printing technology has shown significant advantages in prefabricated buildings due to its non-molded characteristics, and its demolition-free model points are incomparable with traditional processes. However, the technology's unique layer-by-layer stacking process creates weak zones between layers and strips of 3D printed concrete (3DPC). When a large number of weak areas are located in the same cross-section, it is easy to cause concentrated damage, which poses a hidden danger to the overall safety of the component. Different printing paths can effectively control the distribution characteristics of weak areas between strips. In this study, a wavy printing path is innovatively proposed, which aims to disperse the interface weak areas between the printing strips of each layer and avoid the upper and lower layers from aligning with the same cross-section. By adjusting the wave twist amplitude (with the curvature angle of the printing path as the variable), the effects of the path on the compressive performance, anisotropy, interlayer adhesion and inter-strip adhesion properties of 3DPC were systematically evaluated, and the feasibility of improving the mechanical properties of 3DPC without additional cost was verified. At the same time, the mechanism of printing path on interface performance is explored. The results show that the overall performance of 3DPC with wavy path (especially in terms of anisotropy and tensile strength between strips) is significantly better than that of traditional straight path. The inter-strip tensile strength increases exponentially with the increase of curvature angle. When the curvature angle is 90°, the inter-strip interface bonding strength reaches 2.48 MPa, which is 52.34% higher than that of the traditional path. The tensile strength of the interface is 2.82 MPa at the curvature angle of 70°, which is 36.89% higher than that of the traditional path. Based on the experimental data, a prediction model for the tensile bond strength of the 3DPC interstrip interface and the tensile bond strength of the 3DPC-NC interface was established, which had good prediction accuracy and provided a valuable theoretical reference for the development of concrete 3D printing technology.