Influences of Printing Pattern on Mechanical Performance of Three-Dimensional-Printed Fiber-Reinforced Concrete

Underperformed interfacial bond and anisotropic properties are often observed in three-dimensional-printed concrete, where the printing pattern is unidirectional. Such issues could be potentially alleviated by replicating microstructures of natural materials or applying different architectures, where printed layers are arranged into unique and unconventional patterns. Furthermore, the quest to develop printing methods for highly complex or self-support concrete architecture could benefit from these nature-inspired patterns. In this work, the influences of different architectural arrangements of layers on mechanical properties of hardened concrete on compressive and flexural strengths are investigated. Specifically, unidirectional (0°), cross-ply (0°/90°), quasi-isotropic (0°/ ± 45°/90°), and helicoidal patterns (with pitch angles of 10°, 20°, and 30°) are used to create unidirectional, bidirectional, and multidirectional layers in printed objects without and with 0.75% by volume of 6 mm-long steel fibers. The experimental results demonstrate considerable improvements in the flexural strengths of nontraditional specimens without steel fibers over the unidirectional control with a few exceptions. Among investigated patterns, the quasi-isotropic demonstrates significant influences in both compressive and flexural responses of printed concrete samples without steel fibers. The addition of steel fibers leads to noticeable improvement on both compressive and flexural strengths of samples in any pattern compared with their counterparts without fibers. Besides, the inclusion of steel fibers into unconventional layups (cross-ply, quasi-isotropic, and helicoidal patterns) leads to the alleviation of directional dependence of mechanical properties, which is a limitation of the unidirectional samples with fibers. Of all helicoidal patterns, the one with a 10°-angle layup is shown to be more beneficial to the flexural strength enhancement and damage resistance in bending. X-ray microcomputed tomography measurements are performed to visualize the direction and distribution of fibers.