Effect of printing patterns on pore-related microstructural characteristics and properties of materials for 3D concrete printing using in situ and ex situ imaging techniques

3D printed samples have the unique feature of being layered and laminated to form a structure. The pore distribution characteristics around layers and filaments differ from cast specimens and significantly affect the mechanical properties. To produce high-quality 3D printed elements in terms of structural integrity and long-term performance, it is essential to understand their microstructural characteristics both during the printing process and after curing. In this paper, an in situ imaging analysis technique is proposed to examine the effects of printing patterns on pore-related characteristics and their correlation with the mechanical properties of 3D printed concrete. The interfilament voids of fresh 3D printed specimens, one of the most important factors affecting the mechanical properties, are investigated using in situ images obtained during the printing process and through an ex situ image analysis using X-ray micro-computed tomography. Additionally, the spatial distributions of pores in entire printed prisms after one-day curing are obtained by ex situ imaging analysis. Through combining in situ and ex situ analyses, it was found that the changes in pore distribution during hardening are different depending on the printing patterns. The characteristics of interfilament voids significantly impact the performance of the printed sample, resulting from the anisotropy of the pore distributions. The obtained results provide insight into a real-time image-based microstructural monitoring technology for 3D concrete printing, which can be utilized to suggest the optimal printing patterns for the purpose.