Integrated non-destructive assessment of 3D printed UHPC microstructure using X-ray computed tomography and ultrasonic waves

3D printed ultra-high performance concrete (3DP-UHPC) has gained significant attention for its unique fiber distribution and superior mechanical performance characteristics. This study employed X-ray computed tomography (X-CT) imaging and ultrasonic techniques to quantitatively analyze the internal pore structure and fiber distribution of 3DP-UHPC. The findings revealed that the compressive strength of 3DP-UHPC exhibited anisotropy, following the order Z > X > Y. The pore volume distribution showed substantial variability, with the projected pore lengths along the X, Y and Z axes following the trend X > Y > Z. This uneven distribution contributed to reduced mechanical performance. Steel fibers exhibited a distinct 'cross-like' alignment within the 3D printed plane. Additionally, variations in amplitude, compressive strength, and average wave velocity showed consistent trends, all of which were positively correlated with wave velocity. These insights provide a theoretical foundation for improving non-destructive evaluation techniques and optimizing the performance of 3DP-UHPC.