3D concrete printing of bioinspired Bouligand structure: A study on impact resistance

For extrusion-based 3D concrete printing, research work on mechanical properties mainly focuses on static behaviour, whereas dynamic performance has been rarely reported. Meanwhile, biomimicry is getting increasing interests in the field of 3D concrete printing, due to its advantage of improving structural properties and optimising material usage by learning from nature. Inspired by the Bouligand structure in the dactyl club of mantis shrimp, this study explored the impact resistance of 3D-printed concrete specimens with and without steel fibres under drop weight impact tests. Four different printing patterns were designed, including the pitch angle of 0˚, 15˚, 30˚ and 45˚. For fibre-reinforced specimens, those with helicoidal patterns performed better than the one with unidirectional pattern (i.e. 0˚) in terms of impact duration, peak impact force and energy absorption. For specimens without fibres, the effect of pitch angle on the impact resistance was insignificant. The influence of pitch angle on impact resistance was more profound when specimens were incorporated with steel fibres during the printing process. Micro-CT images showed the size and geometry of internal pores were influenced by the printing pattern, thus affecting the mechanical response. Meanwhile, fibre-reinforced specimens presented complex cracking mechanisms with mixed modes, including crack deflection, twisting, branching, bridging and micro-cracks. Analysis on fibre orientation revealed the fibre alignment in the direction of the toolpath, leading to effective crack-bridge actions by steel fibres as the crack propagated during the impact process.