Large-scale 3D printing concrete technology: Current status and future opportunities

Three-dimensional (3D) printing construction techniques have been increasingly developed in recent years and transferred into practical applications in some instances. However, knowledge of the differences between largescale 3D printing and laboratory 3D printing is still limited. In this review, large-scale extrusion-based 3D printing concrete (3DPC) technologies are subdivided into three categories according to different printed objects and construction processes: 3D printing elements, 3D printing formworks, and monolithic 3DPC on-site. The different printability requirements of large-scale and lab-scale 3DPC are compared in this paper. Then practical problems of large-scale 3DPC are discussed, including economic and environmental optimizations, reinforcement constructions, preparation and remix of concrete, and different large-scale 3D printing systems. The construction details of reinforcements implemented with various 3D printing technologies are reviewed based on several pioneering projects. Finally, some recommendations for future work are provided for facilitating the use of largescale 3DPC technology in practice of construction.