Encasement of Pre-Placed Reinforcement in Injection 3D Concrete Printing (2025-12)¶

Injection 3D Concrete Printing (I3DCP) is a new additive manufacturing technique, where material is robotically injected into a carrier liquid where it remains suspended. The injection of concrete into a non-hardening carrier liquid, has proven to be successful at producing complex and filigree concrete structures. I3DCP is capable of overcoming the directional limitations faced by other additive fabrication methods as it is possible to print in 3-dimensional space. However, this technology has been limited to producing compression-only structures, as its thin concrete strands are incapable of withstanding significant tensile loads. A potential solution is the introduction of reinforcement into the concrete structures. This study focuses on the injection of a fine grain concrete into well-characterized carrier liquids where spatially fixed rebars are placed to be fully encased. The effect of material- and process related parameters on the encasement quality are studied. The rheological parameters of the carrier liquid are varied by solid volume fraction (ranging from 33.3 vol.-% to 44.4 vol.-%). The shape of the nozzle (straight tube/ U-slot) and the nozzle traverse speed (ranging from 40 mm/s to 100 mm/s) are systematically studied as part of the process parameters. The quality of the encasement is evaluated by image analysis. It is observed that with increasing yield stress of the carrier liquid the reinforcement is less encapsulated while carrier liquids with a low yield stress are incapable of supporting the injected concrete. These effects can be counteracted by changing the nozzle shape and/or print speed. Finally, the potential and limitations of using reinforcement bars in I3DCP are discussed.