This study systematically investigates the hardened properties, durability and void distribution of large-scale 3D printed cement-based materials (3DPC). Experimental results indicate that 3DPC has higher compressive and flexural strengths, lower drying shrinkage, better resistance against sulfate attack and carbonation than mold-cast cement-based materials, but lower resistance to frost damage and chloride ion penetration. Computed tomography scanning reveals that voids in 3DPC are strongly oriented along the printing direction. Furthermore, the voids are much more inter-connected and even continuous among the printed filaments. This unique void distribution is the origin of anisotropy for 3DPC and can explain the determined directional dependency of mechanical strengths and durability performance. Along the printing direction, the more connected voids render more channels for gas and liquid to penetrate into 3DPC.