Comparative Analysis of Polypropylene, Basalt, and Steel Fibers in 3D Printed Concrete (2025-01)¶

This study conducts a comprehensive analysis of the effects of polypropylene (PP), basalt, and steel fibers on the workability, printability, rheological, and mechanical properties of 3D printed concrete (3DPC) with varying fiber contents and lengths. Tests include jump table, concrete strip extrusion (φ20 ×500 mm), thin-walled square tube buildability (200 ×200 ×280 mm), and strength evaluations, along with SEM analysis of the fiber-matrix interface. Results show that fiber content and length affect flow spread: PP fibers reduce flow due to higher cement paste consumption, basalt fibers reduce it due to water absorption, and steel fibers cause the most reduction due to density and interlocking. When material flowability is between 170 and 195 mm, the extrusion strip width is uniform, with strong height retention, especially with steel fibers. All fibers increase yield stresses, with steel fibers having the most impact. Optimal mechanical properties occur at fiber contents of 0.5 % for PP, 0.3 % for basalt, and 0.7 % for steel. Compressive strength in the Z-direction increases by 11.5 %, 4.7 %, and 22.5 %, and flexural strength in the Zx-direction increases by 26.4 %, 12.1 %, and 71.1 %, compared to un-reinforced concrete. Steel fibers are the most effective at enhancing strength due to their stiffness and matrix interlocking. SEM analysis shows that PP fibers are mostly vertically oriented in print strips, with interlayer fibers parallel to the cross-section. Failure modes include pull-out and rupture. Basalt fibers are more disordered and fail mainly through rupture. Steel fibers align well, with pull-out as the main failure mode, providing strong interlocking with the cement matrix for better energy absorption.