# Overview of the Development of 3D-Printing Concrete: A Review
## 7 The Problems and Prospects of 3D-Printing Concrete  
### Existing Problems  
Many challenges and technical problems have always existed in the field of 3D-printing concrete, although much research has been undertaken. A brief list is as follows:  
1. The problem of accurate conversion between software design and real architecture. In contrast to the traditional building structure, 3D-printing construction technology requires the design of the building model on the computer, and then converts it into a physical object through an automated program. The design software has become an important part of the preparation phase of the 3D-printing construction technology, but there are certain errors between the software 3D design and the entity in architectural printing, which lead to construction quality problems and limit the development of 3D-printing concrete technology. How to realize the conversion between software and reality is an indispensable step in the development of printing concrete. 2. The feasibility of complex architectural printing. The mechanical properties of 3D-printing construction technology are still at the stage of research and development. Although it can be applied to the construction of low-rise and large-area buildings, one-time 3D-printing cannot be done for common high-rise buildings. Thus, the feasible method is to print prefabricated ones first and re-assembly of parts, which is similar to prefabricated buildings. Thus, the advantage of rapid prototyping is lost. Difficulties lie in the high-rise buildings of tens of meters or even hundreds of meters. First of all, it requires a printer compatible with the height of the building. Secondly, to obtain the structural strength of the high-rise building and the problem of the steel bar structure in the building structure, a reasonable solution is needed. 3. The requirements of building materials is another problem. Most 3D printed buildings are made of high-strength special concrete materials. Ordinary cement cannot meet the requirements of building performance and printing process. It can be seenthat the requirements of 3D-printing for material performance must be considered. The 3D-printing building mainly uses printer nozzles to spray materials to build walls. This spraying method not only requires certain stress and mechanical molding characteristics, but also has certain requirements for the quality of coarse and fine aggregates. The requirements for the quality of aggregates are very high, and even new crushing processes are needed. The effect of admixtures in ordinary concrete may be due to the change of materials, which makes it play a role in the specific system of 3D-printing buildings, and even its mechanism of action also changes. Thus, to realize the printing of three-dimensional buildings, materials are the first problem to be solved. 4. The problem of molding height. The current 3D-printing concrete technology is still in the stage of plane expansion. It can be applied to the construction of low-rise and large-area buildings. However, it is not possible to print the widely used high-rise buildings. It can only be printed by first printing prefabs and then assembling them. To print dozens of floors of buildings, it is necessary to design a giant 3D printer to solve the problem of structural strength of large buildings and the printing of steel bars in buildings. 5. The problem of anisotropy. This is one of the main challenges to limit the development of 3D printed concrete. The main reason for the anisotropy is that the internal structure of the layers or the internal structure of the material is different due to the layer-by-layer printing, which causes the difference of mechanical properties when the printed components loaded in different directions. It is also related to various factors such as material properties, nozzle types, and steel bar layout besides the impact of the layer-by-layer printing construction process. 6.