Experimental Study on the Role of Defect-Driven Interfaces and Porosity in Governing the Mechanical Behavior of 3D-Printed Concrete (2026-03)¶

Additive manufacturing of cementitious materials, particularly three-dimensional concrete printing, has emerged as a transformative approach for sustainable and efficient construction. However, the anisotropy and porosity inherent to the printing process remain critical barriers to structural reliability. This study presents a comprehensive experimental program to evaluate the mechanical behavior of 3D-printed concrete (3DPC) under compression, flexure, pull-out, and double shear loading scenarios, supplemented with X-ray micro-computed tomography-based porosity analysis. An optimized ultra-high-performance concrete-based printable concrete tailored for extrusion was prepared, and mechanical responses of printed specimens were benchmarked against mold-cast counterparts. The results reveal that 3DPC exhibits direction-dependent behavior, with compressive and flexural strengths reduced by 25.6% and 22.5%, respectively, compared with cast concrete. Pull-out tests indicated lower initial stiffness in printed specimens, with failure modes dominated by interlayer and interstrip debonding rather than steel–concrete adhesion.