Spray-based 3D concrete printing parameter design model: Actionable insight for high printing quality

A spray-based 3D concrete printing parameter design model to design and optimize printable concrete is proposed. The effects of different relatable printing parameters, such as nozzle travel speed (V), spray nozzle diameter (A), and spray standoff distance (D) on spray-based 3D printability and printing quality are investigated systematically. The hydration mechanism of spray-based 3D printed concrete is then explored in terms of mechanical performance, layer moisture content, micromorphology, and pore structure. The experimental results show that the printing quality of the printed concrete can be effectively improved by optimizing the relatable printing parameters. Based on the three key printing performance indexes of layer thickness, surface flatness, and rebound rate, the spray-based 3D concrete printing parameters design model beta = f(V,A,D) is proposed. In the high-precision zone of beta [0.7,1], the printing parameter V70A8D60 (beta = 0.71) is selected to further verify the effectiveness of the model. It shows that the spray-based 3D printing process with appropriate printing parameters ensures the excellent hydration process of the printed concrete. Compared with those of the cast counterpart, the flexural, compressive, and splitting strengths of spray-based 3D printed V70A8D60 specimens increase by 5.67-14.48 %, 15.79-29.79 %, and 19.95-37.27 %, respectively. Further, high-pressure spraying in the spraybased 3D printing process optimizes the pore structure of the printed concrete with a 69.4 % decrease in total porosity. An "Olympic rings" convex structure with different accuracy grade parameters in the beta model is designed and fabricated to demonstrate the feasibility and practical applicability of the currently proposed parametric design model.