Enclosing Reinforcement Structures in Shotcrete 3D Printing (2023-10)¶

Integrating reinforcement into existing concrete 3D printing processes represents one of the key challenges in further automating the additive manufacturing of structural concrete components. Several different reinforcing approaches are currently being investigated. In this context, the Short Rebar Insertion (SRI), as well as the use of prefabricated reinforcement structures, are potential strategies. A common feature of both methods is that rebars protrude from the already printed concrete in different orientations during the printing process and must be embedded in the subsequent concrete layers. Due to the spray application, Shotcrete 3D Printing (SC3DP) offers a good basis for realizing such reinforcement enclosures without the need for specially adapted nozzles, as often used in material extrusion. However, it is essential to systematically analyze the effect of reinforcement properties, such as reinforcement orientation, and material properties, such as accelerator dosage, to define the application boundaries. For this reason, the present study investigates the enclosing of different reinforcement geometries (spacing, inclination, crossings) with unaccelerated and accelerated fine-grained concrete to evaluate the enclosing process. It is shown that all centrally positioned reinforcement structures could be homogeneously enclosed in the SC3DP process. However, for a small rebar spacing and for accelerated material, the eccentric reinforcement structures increasingly act as a blocking element for material spreading. Furthermore, the accumulation of concrete on the top of the reinforcement during spraying creates a shielding effect that increasingly leads to void formation. Finally, recommendations are made for the enclosure of protruding reinforcement structures in SC3DP.