Low-velocity impact performance of biomimetic 3D printed engineered cementitious composites beams

3D printed engineered cementitious composites (ECC) exhibit remarkable ductility and superior crack control that enhances the load-bearing capacity and toughness of 3D printed structures. Optimising the printing paths across various orientations can effectively reduce the anisotropy in mechanical behaviour of 3D printed concrete. To date, a comprehensive study on energy dissipation in 3D printed ECC under low-velocity impact is still lacking. This paper presents a systematic investigation into both cast and 3D printed polyethylene (PE) fibrereinforced Bouligand ECC beams using three-point bending and low-velocity impact tests. Results show that the extrusion-based 3D concrete printing (3DCP) process, combined with varying pitch angles in the printing path, significantly enhances quasi-static and low-velocity impact bending performance, particularly in terms of peak load and energy absorption. Energy dissipation under low-velocity impacts was quantified using digital image correlation, with the ranking: 3DP-15 > 3DP-90 > 3DP-0 > 3DP-45 > 3DP-30 > Cast. The enhanced energy dissipation capacity of 3D printed ECC beams under low-velocity impact, compared to cast ECC beams, is primarily attributed to improved fibre bridging from the extrusion-based 3DCP process, crack deflection/twisting energy consumption at interfaces, mechanical interlocking, and sliding friction due to the unique rough surface of printed ECC. Additionally, variations in the energy dissipation capacity of 3D printed ECC beams with different pitch angles under low-velocity impacts may result from a competitive hybrid fracture mode, combining crack deflection/twisting and crack bridging along interfaces. These insights contribute to improved multidirectional low-velocity impact resistance in 3D printed ECC and promote broader applications of 3DCP technology in structural engineering.