The development of 3D printing concrete technology


3D printing technology is a major opportunity for the development of concrete industry, 3D printing concrete technology has become an important direction for the development of concrete industry. And China has a great advantage in this regard, the network before the construction of 3D printers have been a substantial coverage, such as Shanghai Ying Chuang, Beijing Tongzhou Beijing Chinese business Tengda Industry and Trade Co., Ltd., as well as Gansu farmers uncle also own Made a building 3D printer. Next, Xiaobian briefly introduced the current situation and the latest development of 3D printing concrete technology and its materials, construction and the technical problems of 3D printing concrete technology, and prospects the future of 3D printing concrete technology, and put forward possible research direction.

In recent years, as the "third industrial revolution" iconic technology, 3D printing technology to lead the trend of the times, quickly into the various research areas, from industrial design, aerospace to medical and other fields have appeared 3D print footprint, which The traditional social production will have a huge impact, to change the future of the world is creative technology. Similarly, 3D printing technology and concrete technology combined with 3D printing concrete technology, will be the concrete development process on a major turning point. Xiaobian will use 3D printing technology as the starting point to introduce the development status of 3D printing concrete technology and the contribution to the construction industry, combined with the understanding and existing problems of 3D printing concrete technology, the future of 3D printing concrete technology and research trends The

Concrete material is one of the most important civil engineering materials in today is society, making an invaluable contribution to the development and construction of human society. With the development of social science and technology, the high energy consumption and high pollution of concrete in the process of production and application And other issues gradually highlighted, as a constraint on the development of concrete materials, a major resistance. In order to meet the needs of sustainable development of society, the performance of concrete itself gradually to high strength, high performance and other direction, at the same time, the emergence of new technologies for the sustainable development of concrete provides a new direction.

3D printing concrete technology

3D printing technology is based on the development of 3D printing technology used in the construction of concrete technology, its main working principle is to configure the concrete slurry through the extrusion device, under the control of three-dimensional software, in accordance with the pre-set Good print program, extruded by the nozzle to print, and finally get the design of concrete components (Figure 2 (a) shown). 3D printing concrete technology in the printing process, without the traditional concrete molding process in the process of supporting the mold, is a new concrete moldless molding technology. In 2012, researchers at the University of Loughborough in the United Kingdom developed a new type of concrete 3D printing technology, as shown in Figure 2 (b), under the control of computer software, using a highly controllable extruded cement Slurry material, the completion of the precise positioning of concrete panels and walls of the hole in the print, to achieve a super complex large-size building components designed for the appearance of a unique concrete building opened a door.

1.3D print concrete

With the advent of 3D printing concrete technology, ordinary concrete has been unable to meet the needs of its technology, the concrete performance of the further requirements, respectively, reflected in the construction of fresh concrete and hardened concrete mechanical properties and durability, the United Kingdom Loughborough University is TTLe et al. Conducted a related study. For the new concrete slurry, in order to meet the requirements of 3D printing, must meet the specific performance requirements. First, it is extrudable. In 3D printing concrete technology, the concrete slurry is extruded through the nozzle at the front end of the extrusion device. Therefore, the size of the slurry in the slurry is determined by the size of the nozzle, and it is necessary to strictly control and eliminate The emergence of large aggregates, in the printing process will not be blocked to ensure smooth extrusion of the slurry.

Second, the concrete slurry to have a good cohesion, on the one hand, better cohesion can ensure that the concrete through the nozzle in the process of extrusion, the slurry will not be due to the performance of their own reasons, to avoid missing ; On the other hand, 3D printing is the accumulation of layers to get the final product, therefore, the combination between layers and layers of 3D printing concrete is a weak link, is an important factor affecting the hardening performance, and good cohesion Can minimize the negative impact of the print layer. Finally, the extrudability and cohesion can ensure that the pre-printing and hardening of the performance, but it is difficult to ensure that the printing process can be carried out smoothly. In the process of 3D concrete printing, it is necessary to require the printed part of the state to maintain a good, there will be no collapse, tilt and other interruption of the construction of the phenomenon, which made the construction of the concrete slurry requirements (Figure 3 Show).

3D printing concrete technology will also have a greater impact on the performance of hardened concrete. During the printing process, the concrete is extruded in strip shape. The bond between the strip and the strip is an important factor in determining the pore structure of the hardened concrete. Poor cohesion will lead to large and large inside of the printed concrete structure Porosity (as shown in Figure 4), will also have a significant impact on the durability of concrete; for strength, the use of printing technology will cause the loss of concrete strength, resulting in the strength of printed concrete is lower than the same ratio Of the molding concrete, at the same time, the printing will also make the strength of the concrete characteristics of the opposite sex, the strength of the level determined by the printing direction; In addition, the water conservation of the performance of printing concrete also have a greater impact, The researchers i research has also been confirmed [7], mainly because the conservation of water will have a certain effect on the microstructure of the printed concrete, filling the concrete produced during the printing process to improve the performance of the printed concrete.

2.3D Print concrete construction

As 3D printing concrete appears in the researcher is field of view, 3D print buildings are also produced. Italian researcher EnricoDini invented the world is first large-scale building 3D printer, the bottom of the printer there are hundreds of nozzles, can be ejected magnesia adhesive, sprayed on the adhesive sand can be gradually cast stone solid, through a Layers of adhesives and sand combine to form stone buildings, and the successful use of building materials to print out the building 4 meters high (as shown in Figure 5). On this basis, he and the Dutch architect JanjaapRuijssenaars work together to use this 3D building printer to print a building "Mobius ring" -like building, to participate in the European 3D print competition [8], which is 3D Print concrete technology in the construction industry bold practice. Recently, Shanghai Qingpu appeared a number of 3D printing houses, the development of Ma Yi and the use of recycled construction waste and glass fiber as a printing material, the use of self-designed assembly printing machinery in 24 hours to complete the 10 200 square meters of building " Print ", but its use of materials and structure of the bearing capacity, durability is still worth considering.

Before a Dutch construction company has also started a building to print, the construction is mainly through the 3D printer to print out the prefabricated pieces like building blocks, in order to complete the print. In the printing process of 3D printing concrete, the process of accumulation of concrete layers, inevitably in the printing components on the surface of the step effect, the surface roughness, not only affect the appearance, but also may lead to accuracy error, from the figure 6 can be clearly seen, the printed component surface there are horizontal stripes, the level is more obvious, the surface flatness to be beautified. In order to deal with such problems, usually using two methods: First, reduce the caliber of the print nozzle, reduce the height of the steps, this method will reduce the printing speed, affecting the construction efficiency, and can not guarantee the surface to achieve the desired flatness; Second, after the follow-up in the formation of smooth processing, this method need to repeat the work, time-consuming and laborious. In order to solve these problems in the process of 3D print construction, Professor Behrokh Khoshnevis of the University of Southern California presented ContourCrafting. Contour building technology is a process of building construction using 3D printing technology, including the Extrusionsystem and the Fillingsystem (Figure 7 (left)), the principle is to first external contour Of the printing, and then fill the material to the inside, the formation of concrete components.

The biggest feature of the contour building process is: the mud on the nozzle (as shown in Figure 7 (right)), mud knife to ensure that the building can be printed at the same time the surface can be a good solution to the problem of uneven 3D printing surface The In addition, the outline of the building process can be in the 3D printing at the same time, to achieve reinforcement of concrete components, you can also further try high-rise building print construction. Based on the 3D printing technology, the silhouette of the silo is more advantageous. On the one hand, the surface of the building is smooth and the smoothness and accuracy of the surface of the building are improved, and the construction is avoided. , You can also increase the thickness of each layer of printing, improve the building construction efficiency, can be printed within 24 hours to complete a 2500 square feet of the house. In addition, the presence of the filling system in the print design can be filled with internal materials as needed to greatly improve the structural performance of the printed building.

3.3D print concrete problems

The current 3D printing technology is in the development phase of the trial, for its performance and application are in the exploratory stage, therefore, inevitably there will be some problems.

(1) raw material problems. 3D printing of concrete relative to the traditional mold-forming concrete on the raw material requirements are more stringent, ordinary cement may not be able to meet the requirements of building performance and printing technology, the quality of coarse aggregate requirements will be higher, or even to adopt a new crushing system , And for the admixture in the concrete system to play the role and mechanism of action may also change.

(2) the theory of mix theory. 3D printing concrete technology put forward special requirements for the new properties of concrete such as cohesion, extrusion and buildability. At the same time, the printing process has a great influence on the later hardening performance of concrete, which is not simple According to the water-cement ratio, sand rate and other parameters can be adjusted to meet. Whether the concrete prepared according to the existing concrete mix ratio theory can meet the working requirements of 3D printing well, the requirements of the mechanical properties and durability index after printing hardening are still to be determined, which requires a new angle Theory to better adapt to 3D printing concrete technology.

(3) software problems. Unlike traditional concrete construction, 3D printing concrete needs to complete the construction of the model on the computer, and then through the automation process to convert it into physical, so the design software to become a 3D printing technology, an important part of the preparatory stage, and how to achieve software The transformation between reality and the reality of the development of concrete indispensable steps.

(4) forming height problem. The current capacity of the 3D printing technology used in the technology is still in the plane expansion stage, can be applied to the construction of low-rise large-scale buildings, and for the widely used high-rise buildings can not be printed, only by printing pre-pieces, and then assembled Way to achieve, at the same time, to dozens of layers of the building to print out, you need to design a giant 3D printer to solve the problem of structural strength of large buildings, as well as building steel bar printing problems. In addition, 3D printing concrete in the production process, security measures, etc. will have a greater change, will cause more or less problems, which are to be further research and discovery of the researchers.

3D printing concrete outlook

With the development of science and technology, willing to engage in first-line manual labor less and less, as a labor-intensive concrete construction industry will usher in a huge challenge, combined with 3D printing technology, the emergence of 3D printing technology, is undoubtedly a The great gospel, has a very broad development prospects. 3D printing concrete technology in the construction process to eliminate the mold demolition of the cumbersome process, to a large extent simplify the construction process, making the construction rate can be increased to 10 times more, but also can achieve the full use of concrete, reduce the cement The use of the building, but also can improve the service life of the building, reduce the production of construction waste, reduce duplication, at the same time, 3D printing machinery requires only a few technical staff control, reducing the number of construction workers, is in line with the development of today is society trend. In addition, 3D printing concrete technology can achieve a variety of shapes of building printing, less demanding on the environment, can be applied to the exploration of outer space, the rapid completion of space base construction.

At present, 3D printing concrete technology is in the development stage, in order to realize the universalization of 3D printing concrete technology application, need to solve the problem of its key technology. Future 3D printing concrete technology research and development can be carried out from the following aspects:

(1) Study on concrete materials. Although the University of Loughborough is TTLe and others on the 3D printing concrete part of the study, put forward some of the 3D printing concrete needs to have the performance, but mainly based on the current stage of 3D printing concrete technology preliminary understanding, the lack of more systematic Theory, in-depth study. In order to make 3D printing concrete technology can be developed rapidly, it is necessary to systematically study the raw materials and preparation theory of concrete. Therefore, the new concrete mix ratio theory and new raw material requirements need to be improved according to the performance requirements. Will be the main research topic in the development of 3D printing concrete technology.

(2) supporting hardware and software research. 3D printing concrete technology is the computer software and printing machinery in collaboration with the process, how to computer three-dimensional model through the software control of the printing device to become a kind, better combined with the automation process, and to achieve the best results , It will be a long process.

(3) the printing process research. How to arrange the order of printing in a reasonable way, control the print head of the full range of climbing are all important factors to determine the efficiency of printing, but also in the future study of the need to pay attention to. At the same time, the current 3D building printing process can be achieved by the height of the print is subject to greater restrictions, and social development has made concrete construction gradually to the high direction, which requires a new printing process to achieve high-level printing and high-level development to be resolved The structural strength, reinforcement and other issues.

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