Anisotropic behavior in bending of 3D printed concrete reinforced with fibers

The incorporation of fibers is an effective way for the reinforcement of 3D printing concrete. However, researches referring to effect of fibers on the anisotropy properties were limited. Therefore, the anisotropic behavior of fiber reinforced cement-based material for 3D printing under bending were carefully examined. With the addition of polyethylene (PE) fibers, the specimen failure was no longer dominated by the weak interface and the flexural strengths in all of the three directions were significantly improved. The post-peak performance was directly related to the content of fibers and a suitable fiber length should be selected. Microstructure analysis showed that the uniform and aligned orientation fibers were key factors leading to the increase of ultimate strength and post-peak behavior. However, 3D printed specimens still demonstrated obvious anisotropic behavior. The flexural strengths in the directions parallel and perpendicular to the printing element within the printing plane were highest and performed similarly, while the strength in the direction orthogonal to the printing plane (across the layers) was the lowest. It is believed the findings can provide help for understanding the role of PE fibers in extrusion-based 3D printing concrete.