Trans-layer and inter-layer fracture behavior of extrusion-based 3D printed concrete under three-point bending

This paper presents a systematic study on the effect of layer-by-layer printing process on the fracture behavior of hardened extrusion-based 3D printed concrete (3DPC). Based on three-point bending tests on center-notched beams, the fracture response of printed specimens with two fracture patterns including crack propagation across layers (trans-layer fracture) and crack propagation along layers (inter-layer fracture) was compared with that of cast specimens. The fracture mechanism of 3DPC was explored using the fracture parameters and fracture process zone (FPZ) characteristics. Experimental phenomena can be explained by the additional interlaminar cracking in FPZ of concrete introduced by the layer-by-layer stacking process. It could produce a toughening effect if cracks propagate through layers, as it is beneficial to reduce stress concentration and improve deformability. In the printing process design of 3DPC, such feature can be rationally utilized to transform the process-induced weak interfaces from inherent defects to toughening means.