Design and Function Classification Study of Multi-Bin 3D Printing Nozzle for Foam Concrete with Enhanced Performance

In response to the urgent demand for lightweight and thermal insulation building materials in remote island and reef infrastructure under harsh marine environments, this paper designs a new multi-bin functional graded 3D printing nozzle and relies on the optimal base material to prepare functionally graded foam concrete. The mechanical and impact resistance properties of the layered gradient foam concrete are systematically explored. The developed nozzle consists of 4 independent auxiliary bins and 1 main bin and is equipped with a blade-type spiral structure and conical nozzle. The parameters are optimized through CFD flow field simulation, and the pitch of the auxiliary screw is set at 15 mm, the pitch of the main screw at 30 mm, and the main shaft speed at 40 r/min. This structure can achieve independent transportation of multi-component slurries and avoid material mixing. Three base materials with fiber reinforcement, high-density aggregates, and porous insulation are formulated, and the O1-O2-O3 three-layer gradient arrangement scheme can simultaneously achieve the synergistic improvement of mechanical properties and pore-structure-based thermal insulation potential. Compared with homogeneous foam concrete, the optimal graded specimen has a 60% increase in compressive strength, a 100% increase in flexural strength, and, in the specific H1-H2 comparison for which quantitative drop-hammer data were obtained, the graded specimen required more repeated impacts to first cracking and to failure than the homogeneous control, indicating improved resistance to repeated impact loading. The complete set of printing equipment and gradient composite materials can provide a preliminary technical basis for further development of intelligent on-site construction on islands.