# Overview of the Development of 3D-Printing Concrete: A Review
## 7 The Problems and Prospects of 3D-Printing Concrete
### Development Direction and Key Technology  
Now 3D-printing concrete technology is in the initial stage of development. In order to realize the universalization of the application of 3D-printing concrete technology, it is necessary to solve its existing problems with key technologies. The future research and development of 3D-printing concrete technology can be carried out from the following aspects:  
1. Research on concrete materials. Although a lot of research on 3D-printing concrete materials has been carried out, and some properties that 3D-printing concrete needs have been proposed, it is mainly based on the preliminary understanding of 3D-printing concrete technology, and there is a lack of systematic, theoretical, and in-depth research. It is necessary to conduct systematic and in-depth research on concrete raw materials and compounding theory for 3D-printing concrete technology to develop rapidly. Thus, the new concrete mix theory and new raw material requirementsneed to be improved according to performance requirements. This will be the main research topic in the development of 3D-printing concrete technology. 2. Software and hardware collaboration. The 3D printer needs to recognize the given three-dimensional model to print the building based on the model. The modeling and design software of the architectural field and the CNC software of the 3D printer are effectively docked to realize the seamless recognition of information which is the future software development direction. In addition, using the CNC software to control the hardware device precisely also needs further development. 3. Research on printing technology. How to reasonably arrange the printing direction and order, control the all-round climb of the print head, etc., are important factors that determine the printing efficiency, and it is also an aspect that needs attention in future research. The achievable printing height of the current 3D architectural printing process is greatly restricted, but the development of the society has gradually made the concrete buildings develop toward the towering direction. It requires a new printing process to achieve high-rise printing and development to the high-rise to solve the problem including the structural strength, reinforcement, and other issues. 4. Application of micro characterization technology. The current research still focuses on analysis of macroscopic mechanical properties, while the research on micro-scale can provide theoretical support at the specific material level for the macro-performance. The analysis at the micro level will further deepen and improve the understanding of the mechanical properties of 3D printed concrete. 5. Durability of printing materials. The main focus of study is rheology, buildability, anisotropy of mechanical properties, and interlayer adhesion for extrusion-type 3D-printing concrete. It is necessary to conduct a detailed study on the durability of its material structure considering the service time limit and environment of the printing structure and the building. Quantitatively evaluating the durability of 3D printed concrete is necessary in order to compare the durability of different 3D printed concretes, and finally realize the prediction and improvement of the durability of 3D printed concrete. 6. Hardening performance is one of the important indicators of 3D-printing concrete materials. Due to the existence of weak surfaces between layers, 3D-printing concrete materials have obvious anisotropy. Although researchers have conducted a lot of research on the factors that influence the interlayer bonding performance of 3D-printing concrete materials, and also have proposed some effective interface enhancement methods, the current methods lack flexibility and universality. It is necessary to further study flexible and effective interlayer performance enhancement methods, and optimize the design of the printing structure and path. 7. Strengthening and toughening methods are an important guarantee for the safety of 3D printed concrete structures.