Printability and strength of 3D-printed concrete: Role of mix design and printing parameters

This study investigates the properties of 3D printed concrete mixtures, focusing on rheological characteristics, compressive strength, anisotropy, and printing path effects. Two mixtures were compared: M-1 (90% cement, 10% metakaolin) and M-2 (85% cement, 10% metakaolin, 5% silica fume). M-2 demonstrated superior performance in flowability, shape retention, and buildability, allowing for 164% more printed layers than M-1. Compressive strength tests revealed that 3D printed specimens consistently exhibited lower strength compared to cast specimens due to layering effects and anisotropy. M-2 showed higher compressive strength in both cast and printed cubes. Significant anisotropy was observed in mechanical properties, with compressive strength highest in the X direction and lowest in the Y direction. Flexural strength and elastic modulus also varied depending on loading direction. Among printing patterns, the zigzag pattern with 90-degree rotation between layers (P1) exhibited the highest compressive strength, while circular patterns (P2) showed the lowest. These findings emphasize the importance of optimizing mix design, printing parameters, and loading direction considerations for 3D printed concrete structures.