Influence of Inter-Filament Voids on the Failure Mechanism and Compressive Strength of 3D Printed Concrete (2026-01)¶

Material that has been manufactured using extrusion-based 3D Concrete Printing (3DCP) exhibits anisotropy and larger variability in its mechanical properties. These effects are influenced by the agglomeration of extruded filaments, which presents greater opportunity for air entrapment within the printed volume, as well as creating a network of inter-filament material with different properties. Manufacturing ‘defect free’ is challenging and hence understanding the impact of these defects on mechanical performance is critical, however, there is no published work to date. This reports on an empirical investigation of 155 samples with and without inter-filament void defects. It is demonstrated the presence of the inter-filament voids does influence the failure characteristics: defect free samples exhibit shear failure in all three anisotropic loading directions, whereas the samples containing inter-filament voids predominantly exhibited shear failure in the u-direction (parallel to the filament direction), with a greater occurrence of mixed shear–splitting failures in the v (perpendicular to the filament direction in horizontal plane) and w-directions (layer build-up direction), especially in the w-direction. Inter-filament void size had little effect on the compressive strength in the u and w-direction, while a clear reduction trend in the compressive strength was observed in the v-direction. Therefore, these findings reveal that inter-filament voids introduce direction-dependent failure modes and strength penalties that cannot be captured by design values calibrated for cast concrete. By quantifying the mechanical tolerance envelope of void populations, the study demonstrates the need for recalibrating partial safety factors and acceptance criteria in emerging 3D printed concrete design codes.