Feasibility of Using Ultra-High Ductile Concrete to Print Self-reinforced Hollow Structures

3D concrete printing (3DCP) is facing the challenge of introducing steel reinforcement. Using ultra-high ductile concrete (UHDC) to print self-reinforced structures is a potential method to address the challenge. However, few researches have been conducted in this area. This work aims to demonstrate the feasibility of using UHDC to print self-reinforced structures with hollow sections. 6 different hollow beams without steel reinforcement were printed and tested under four-point loading. The results indicate that the printed beams with hollow sections have multiple cracking, flexural hardening, and ductile failure mode despite the absence of steel reinforcement. The flexural strength of hollow beams ranged from 6.06 MPa to 7.86 MPa. The deflection to span ratio of all printed beams was higher than 1/50 at the ultimate state. The combination of UHDC and hollow structures provides a new concept for 3DCP without steel reinforcement.