Pore Morphology and Orientation-Induced Mechanical Orthotropic Behavior of 3D-Printed Concrete Filament

The mechanical anisotropy of three-dimensional–printed concrete (3DPC) has recently raised significant concerns. This research focuses on the impact of pore morphology and orientation on the mechanical properties of individual filaments. X-ray computed tomography is employed to analysis pore structures of 3DPC filaments and mold-cast concrete, including the porosity, shape, size and orientation of randomly distributed pores. The primary difference in porosity between 3DPC and mold-cast concrete lies in the contribution of large pores. The principal component analysis method is used to characterize the irregular pore shapes and orientation of pores. The results indicate that the ratio of equivalent semiaxis lengths in 3DPC varies significantly with increasing pore volume and is accompanied by pronounced orientation characteristics. A directional ellipsoidal model is established based on the experimental results. The orthotropic elastic properties of the directional ellipsoidal model are calculated using the Mori-Tanaka method and verified by experimental validation. The anisotropic analysis suggests that increasing elongated pores while reducing flattened pores can effectively decrease the degree of elastic anisotropy. Meanwhile, finite-element simulation is used to examine stress distribution around the ellipsoidal pore, and the simulation results indicate that the directional ellipsoidal model reasonably explains the orthotropic strength behavior of 3DPC. However, improving the prediction accuracy continues to be a significant area for advancement, particularly by considering the differences in ellipsoidal pores at the mesoscale.