Studies on the mechanical properties of interlayer interlocking 3D printed concrete based on a novel nozzle

The interlocking can effectively improve the mechanical properties of concrete. However, the strength of 3D printed concrete with interlocking interfaces, fabricated using non-automated methods, is reduced due to the time-consuming interface processing. Additionally, studies on the effects of interlocking on the mechanical properties, failure modes, and anisotropic behavior of 3D printed concrete are not yet systematic. In order to address these issues, a printing forming scheme and nozzles were designed for interlayer interlocking 3D printing, and the mechanical properties of interlayer interlocking 3D printed concrete were tested. Firstly, the forming scheme and nozzles are specifically designed for the preparation of 3D printed concrete with interlocking interfaces between the layers. Furthermore, extrudability tests are carried out to determine the appropriate printing parameters for interlayer interlocking 3D printed concrete. Finally, specimens were printed, and interfacial splitting tests, interlayer interfacial shear tests, and compression tests were conducted. The results reveal that: (1) by utilizing the appropriate extrusion rate of the rotating shaft and nozzle travel speed, better-formed interlayer interlocking concrete filaments can be obtained. (2) the interlayer interlocking 3D printed specimens exhibit higher strength. The interfacial splitting tensile strength is increased by about 14.5–30.7 %, and the interlayer interfacial shear strength is increased by about 7.8–18.0 % compared to those with smooth interlayer interfaces. (3) the interlayer interlocking 3D printed concrete exhibits a reduction in the anisotropic coefficient of about 13.7–25.5 %, and the anisotropy is significantly weakened.