Inter-Filaments Pore Features and Tensile Properties of 3D Printed Concrete with Different Overlap (2026-01)¶

3D concrete printing is an emerging technology with great potential. This research investigated the relationship of the inter-filament overlaps, pore features, mechanical properties and the loading direction on the basis of edge contour identification of the printed filaments. Four inter-filament overlap of 0, 5, 10 and 15mm were selected with a step size of ⅓ of the layer height. Pore features of the specimens at different inter-filaments overlap amounts were characterized and analyzed using CT scanning and SEM. Four destructive mechanical tests (tensile, flexural, splitting and compressive) were conducted. Experimental results demonstrate that the mechanical strength of the specimens increases with the increase of overlap. Compared with the overlap of 0mm, the highest tensile bond strength, flexural strength, splitting strength and compressive strength were achieved at a 15 mm overlap, with increases of 300%, 203%, 156% and 48% respectively. As the overlap amount increases, the tension failure mode transforms from purely adhesive spalling to a hybrid pattern incorporating both adhesive and interlocking fracture. These variations result from the change of the interface contact features. The tensile strength of the specimens lowers when loaded perpendicular to the layers than that loaded laterally. The differentiated behavior results from the altered moment of inertia and load transfer mechanism between filaments. Furthermore, the increase in overlap effectively reduces the mechanical anisotropy of the specimen. The results of this study emphasize the need for more considerations in the overlap amount between filaments.