Research on the Workability of 3D Printed Fiber-Reinforced Concrete Materials

This paper investigates the fundamental workability of 3D printed concrete materials incorporating different fiber types. Fluidity, extrudability, and buildability were proposed as key indicators for assessing printability, evaluated through corresponding test methods, including fluidity tests, filament extrusion tests, and slump tests. The results demonstrate that the optimal ranges for printability are superplasticizer content between 0.35% and 0.45%, accelerator content between 0.60% and 0.85%, and silica fume replacement level between 7.5% and 10%. The incorporation of copper-coated steel fibers led to deteriorated workability, manifested as reduced fluidity, increased fluidity loss over time, poor pumpability, discontinuous extrusion, and low slump, although buildability remained satisfactory. Polypropylene fibers increased the air content in concrete, thereby improving workability; they exhibited good extrusion continuity, appropriate slump and filament width, and favorable buildability. Basalt fibers significantly enhanced air content and workability. However, due to the high stiffness of the fibers, extrusion continuity was only moderate. While the slump and filament width were suitable, the presence of minor voids in the printed filaments resulted in average buildability.