Effect of waste plastic fibers on the printability and mechanical properties of 3D-printed cement mortar

Extensive use and disposal of waste plastic bags have caused significant environmental issues. However, waste plastic bags can be used as fibers to enforce the mechanical properties of cementitious materials. Therefore, the effect of waste plastic fibers on the printability and mechanical properties of 3D-printed cement mortar was investigated in this work. The experiment mainly studied how the parameters of waste-plastic-fiber contents, fiber widths, and printing spacing affected the flowability, buildability, compressive strength, and flexural strength of 3D-printed cement mortar. Additionally, the microstructure of the printed specimens was analyzed by X-ray computed tomography (CT) and scanning electron microscope (SEM). Results showed that the addition of waste plastic fibers improved the flexural strength of 3D-printed mortar to a certain extent, with the maximum value achieved at the fiber content of 0.3%, for the same fiber width and printing spacing. However, as the fiber content increased, the X-CT scan showed that the porosity of the cement mortar gradually increased, resulting in a decrease in its compressive strength. Varying fiber widths had little effect on the mechanical properties of the printed specimens, whereas the spacing between the printing filaments had a significant influence on it. Larger printing spacing lowered the bonding performance between the printing filaments, thereby weakening the mechanical properties of the cement mortar. SEM images revealed that more pores were generated in the printed mortar than in the cast, resulting in the compressive strength of the cast higher than that of the printed. However, the extrusion of the mortar through the nozzle during printing improved the bond strength between the filaments, so the flexural strength of the printed specimens was significantly higher than that of the cast. This study may provide knowledge on recycling waste plastic bags as building materials to alleviate environmental pollution and also reserve resources.