Enclosing Reinforcement Structures in Shotcrete 3D Printing

The Effect of Reinforcement Geometry and Accelerator Dosage on the Formation of the Bond Area

Abstract

Integrating reinforcement into existing concrete 3D printing processes represents one of the key challenges in further automating the additive manufacturing of structural concrete components. A number of different approaches are currently being investigated. In this context, the integration of prefabricated reinforcement structures as well as the process-parallel assembly of reinforcement, e.g. by additive metal arc welding or joining of short rebars, are potential strategies. A common feature of both of these reinforcement strategies is that rebars protrude from the concrete surface in variable orientations during the printing process and need to be enclosed in concrete. Due to the spray application, Shotcrete 3D Printing (SC3DP) offers a good basis for realizing such reinforcement enclosures without the use of specially adapted nozzles. However, it is essential to systematically analyze material properties, e.g. accelerator dosage, and process properties, e.g. reinforcement orientation, in order to define limits for the application. For this reason, the present study investigates the influence of accelerator dosage (0 - 4 %) and reinforcement geometry (spacing, inclination, crossings) on the formation of voids. It is observed that with increasing accelerator dosage, the reinforcement structure increasingly acts as a blocking element for material spreading. The adhesion of the concrete to the reinforcement during spraying creates a shielding effect that increasingly leads to void formation. Finally, the potential and limitations of using prefabricated reinforcement structures in SC3DP are discussed.