Nozzle Criteria for Enhancing Extrudability, Buildability and Inter-Layer Bonding in 3D Printing Concrete (2022-12)¶

The technology supporting 3D Printing Concrete (3DPC) has developed rapidly in recent years. However, inadequate understanding of nozzle-related parameters and a lack of standards for fresh and hardened property testing methods are key challenges to addressing, or rethinking, how to improve printability. To explore how nozzle design and relevant parameters impact upon printability and delineate nozzle operability criteria, this paper conducts a systematic content review of 70 research papers on nozzle design that were published over the past decade (2012 to 2022), focusing on notable gaps in prevailing literature in terms of: current design practices of a nozzle; correlations between nozzle and printability; and current advances in testing methods. Emergent findings suggest that four nozzle-design parameters have the highest potential impacts on printability, viz.: nozzle travel speed; nozzle size; nozzle shape; and distance of the nozzle to the build. Subsequently, the research proposes operability criteria for these four parameters to assist researchers and practitioners set appropriate nozzle-related parameters during printing. Finally, sustainability challenges (such as reduced printing productivity, the blocking problem and limited utilization of waste recycling) in nozzle-adopting are further elucidated upon and recommendations for future work are given. Overall, the findings presented provide both theoretical and practical contributions for nozzle development and open a new horizon in optimization for 3DPC performance.