Design and Experimental Investigation of a 3D Printing Nozzle for Rapid-Hardening Concrete Based on Fluent-EDEM

To address the clogging issue commonly encountered with rapid-setting and hardening concrete, a liquid–solid separation 3D printing nozzle was proposed based on coupled EDEM–Fluent simulations, and its printing performance was verified. First, finite element models of different nozzle types were established, and Fluent simulations were conducted to analyze the slurry flow velocity and turbulence intensity inside the nozzle, from which the optimal outlet shape was determined. Next, the mixing effectiveness of stirring blades with various structural configurations was evaluated using EDEM, and the optimum combination of blade inclination angle, blade number, and stirring speed was identified through orthogonal experiments. Finally, the liquid–solid separation nozzle was designed, and its printing performance was experimentally validated. The results show that the conical nozzle achieves an outlet velocity standard deviation of 0.0144, indicating favorable velocity uniformity. Using the coefficient of variation as the evaluation index, the lowest value is obtained at a blade inclination angle of 40°, with three blades and a stirring speed of 120 rpm, representing the best mixing performance. In a 1 h continuous printing test, the newly developed nozzle operated without clogging, demonstrating the feasibility of the proposed design for short-duration printing tasks. Moreover, the compressive strength of the printed rapid-setting and hardening specimen (A2) was 14.3% higher than that of the conventionally cast specimen (A1), whereas the flexural strength did not exhibit a significant advantage.