Studying the Bond Properties of Vertical Integrated Short Reinforcement in the Shotcrete 3D Printing Process

Additive manufacturing techniques in construction open up new possibilities with regard to geometric complexity as well as structural and material efficiency. However, at this point in time the integration of reinforcement is still subject of research. In the presented experiments, an integration of short reinforcement bars perpendicular to Shotcrete 3D printed layers is investigated. The focus of this study is on the bond quality and the mechanical characterization of the bond behavior between reinforcement and surrounding material for different vertical integration techniques. In this context, three methods are investigated: (1) direct insertion into the printed concrete, (2) insertion into a grouting mortar and (3) screwing the bar into the printed concrete. Steel and carbon reinforcement bars with a diameter of 12 mm are surveyed. The bond of the inserted reinforcement bars is analyzed mechanically by using standardized pull-out tests. Additional micro level analysis of the bond is performed by evaluation of computer tomography images. Directly inserted reinforcement bars show a reduced bonding compared to the other techniques due to a process-related cavity between the reinforcement and the surrounding material. By using the grouting mortar as well as by screwing the reinforcement, a significant increase of bond is achievable.