Comparison of printability and mechanical properties of rigid and flexible fiber-reinforced 3D printed cement-based materials

Since eco-friendly, labor-saving construction technologies are urgently needed than ever, concrete 3D printing technology has gained increasing attention. However, there are still limited studies focusing on reinforcement techniques for 3D printed cement-based materials (3DPCM) which restrict their applications. Herein, we revealed the differences between the influence of typical rigid and flexible fibers on the printability and mechanical properties of 3DPCM. Printability, including buildability and extrudability, was evaluated via fluidity and shape stability tests and verified by printing experiments. The anisotropy ratio was proposed to assess the anisotropic mechanical properties. Furthermore, the fracture energy and bend-press ratio were adopted to assess the toughness. Results indicate that steel, polypropylene (PP) and polyvinyl alcohol (PVA) fibers all increase the buildability but decrease the extrudability of 3DPCM. Compared to steel fibers, PP and PVA fibers have a greater impact on the printability owing to their entanglement. The alignment and wall effect of steel fiber drastically increase the anisotropy in the compressive strength of 3DPCM. PP fibers also intensify the anisotropy in the compressive strength due to their filling effect. Low content of steel fibers and PP fibers both have limited impacts on the toughness and the anisotropy in flexural strength of 3DPCM. The fracture energy of 3DPCM for the loading direction perpendicular to the interface is higher than that for the direction parallel to the interface. Contrary to PP fibers, samples with steel fibers have higher bend-press ratios once the loading direction is parallel to the interface