Improving interlayer adhesion of 3D printed concrete by filament interlocking

A pivotal limitation of 3DPC - 3D printed concrete is the weak bond strength between filaments and layers due to the layer-by-layer fabrication process. In this research, the mechanical properties of printing filaments were investigated and developed to enhance bond strength in both the vertical and horizontal directions. Rectangular self-interlocked filaments fabricated by specifically designed nozzles were used to enhance bond strength between vertical layers. The improvement of bond strength between horizontal filaments on the same plane was obtained by controlling printing trajectories. The effectiveness of self-interlocking filaments was evaluated by printing and testing four types of 3DPC specimens: two with flat and straight interlayers, and two with interlocked interlayers. The disc specimens cut from printed beams and blocks were subjected to indirect tensile tests with different angles between loading and printing directions. The present study employed an advanced testing method, AUSBIT - Advanced Universal Snap-Back Indirect Tensile testing method, in conjunction with both AE - Acoustic Emission and DIC - Digital Image Correlation to capture not only the tensile strength but also to investigate the fracture resistance and post-peak behaviour of 3DPC specimens. The results showed that the indirect tensile strength between layers increased by 48.35 % when tested at a loading angle of 0-degree using a rectangular interlocking pattern, while the zigzag interlocking pattern resulted in a 60.26 % improvement in bond strength between horizontal filaments, compared with the control specimens. The use of lateral displacement control in Brazilian disc tests helped stabilise the fracture process and enabled a reliable analysis of the intrinsic mechanism governing the evolution of fracture and its influence on the overall snapback behaviour. The promising results reveal great potential for further investigation in this direction for strengthening 3D-printed structures. • Rectangular interlocking filaments produced by an innovative nozzle led to a 50 % increase in bond strength between layers. • A 56.3 % increase in bond strength between horizontal filaments can be obtained by zigzag printing strategies. • The advanced technique AUSBIT (Advanced Universal Snapback Indirect Tensile testing) effectively helps stabilise the fracture process to obtain a better result on indirect tensile strength.