Optimization of 3D Printing Nozzle Structure and the Influence of Process Parameters on the Forming Performance of Underwater Concrete

Underwater concrete 3D printing (3DPC) technology, as a pioneering construction process, has demonstrated significant potential in various fields, such as marine engineering, underwater restoration projects, and ecological construction. However, the complexity and variability of the underwater environment pose stricter quality standards for the printed structures. To address this, this study employed a self-developed framed concrete 3D printer and utilized response surface methodology to optimize the structural dimensions of the printing nozzle. Through in-depth analysis of the internal flow field of printing nozzles with various size combinations using ANSYS Fluent 2022R1 software, an optimal parameter configuration was determined, including a nozzle diameter (<i>D</i>) of 55 mm, an inclination angle (<i>θ</i>) of 20°, and a length (<i>L</i>) of 34 mm, ensuring uniform extrusion of the concrete material. Furthermore, this study applied an orthogonal experimental design to systematically investigate the combined effects of screw speed, printing speed, and nozzle height on the print quality and mechanical properties (compressive strength and flexural strength) of underwater concrete 3D printing. The experimental results, presented based on direct observation and analysis, identified the optimal combination of process parameters: a printing speed of 16 mm/s, a nozzle height of 10 mm, and a screw speed of 50 r/min. This combination ensures efficient printing while maintaining the mechanical properties of the printed samples. This study not only provides solid scientific and practical guidance for optimizing the nozzle structure and process parameters of underwater concrete 3D printing technology but also offers innovative solutions to underwater construction challenges in the field of marine resource development and utilization.