In recent years, 3D printing technology, which is the iconic technology of the "third industrial revolution", has led the trend of the times and has rapidly entered various research fields. From the industrial design, aerospace to medical fields, 3D printing footprints have emerged. It will have a huge impact on traditional social production and become a creative technology that will change the future world. Similarly, the 3D printing concrete technology combined with 3D printing technology and concrete technology is a great opportunity for the development of the concrete industry. 3D printing concrete technology will become an important direction for the development of the concrete industry.
Concrete materials are one of the most important civil engineering materials in today's society. They have made invaluable contributions to the development and construction of human society. With the development of social science and technology, high energy consumption and high pollution of concrete in production and application process. Such problems have gradually become prominent, which has become a major obstacle to the development of concrete materials. In order to meet the needs of sustainable development of the society, the performance of concrete itself is gradually developing towards high strength and high performance. At the same time, the emergence of new technologies has also provided a new direction for the sustainable development of concrete.
3D printed concrete technology
3D printing concrete technology is a new technology applied to concrete construction developed on the basis of 3D printing technology. Its main working principle is to pass the configured concrete slurry through the extrusion device under the control of 3D software, according to the preset. A good printing procedure, which is extruded by a nozzle, is printed to finally obtain a designed concrete member. 3D printing concrete technology is the latest concrete moldless molding technology in the printing process, without the need of the traditional concrete molding process. In 2012, researchers at Loughborough University in the UK developed a new type of concrete 3D printing technology. Under the control of computer software, the 3D printing machine uses a cement-based slurry material with highly controllable extrusion properties to accurately position the concrete panels and The printing of the holes in the wall enables the design of ultra-complex large-scale building components, opening a door for a unique concrete building.
1.3D printed concrete
With the advent of 3D printed concrete technology, ordinary concrete can no longer meet the needs of its technology, and further requirements are placed on the performance of concrete, which are reflected in the construction performance of fresh concrete and the mechanical properties and durability of hardened concrete. TTLe et al. at Loughborough University conducted related research. For fresh concrete slabs, specific performance requirements must be met to meet 3D printing requirements. The first is extrudability. In the 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 particles in the slurry is determined by the size of the nozzle opening, and strict control is required to eliminate The appearance of large particle aggregates will not be blocked during the printing process to ensure the smooth extrusion of the slurry.
Secondly, the concrete slurry should have good cohesiveness. On the one hand, better cohesiveness can ensure that the concrete will not break due to the performance of the slurry during the extrusion process through the nozzle, avoiding print omission. On the other hand, 3D printing is a final product obtained by layer-by-layer accumulation. Therefore, the combination between layers is a weak link of 3D printed concrete, which is an important factor affecting hardening performance, and better cohesiveness. The negative impact of the print layer can be minimized. Finally, the extrudability and cohesiveness ensure the performance of the previous printing and hardening, but it is difficult to ensure the smooth printing process. In the process of 3D concrete printing, it is necessary to keep the state of the printed portion intact, and there is no phenomenon that the printing is interrupted due to collapse or tilt, which places demands on the constructability of the concrete slurry.
3D printed concrete technology also has a large impact on the performance of hardened concrete. During the printing process, the concrete is extruded in strips, and the problem of bonding between the strips is an important factor in determining the structure of the hardened printed concrete. Poor cohesiveness can lead to large and large internal printing concrete structures. Porosity will also have a major impact on the durability of concrete; in terms of strength, the use of printing technology will result in the loss of concrete strength, resulting in the strength of printed concrete is lower than that of molded concrete of the same ratio, and printing will also The strength of concrete is characterized by anisotropy. The strength is determined by the direction of printing. In addition, the maintenance of water also has a great influence on the performance of printed concrete. This is also confirmed by other researchers. The reason is that the water conservation will have a certain improvement on the microstructure of the printed concrete, filling the voids caused by the printed concrete during the printing process, thereby improving the performance of the printed concrete.
2.3D printing concrete construction
As 3D printed concrete appears in the researcher's field of vision, 3D printed buildings are also produced. Italian researcher Enrico Dini invented the world's first large-scale 3D printer. The printer has hundreds of nozzles on the bottom that sprays magnesium paste. The sand is sprayed onto the adhesive to form a stone solid. The layers of the ground bond combine with the sand to form a stone building and successfully use the building materials to print a building 4 meters high. On this basis, he worked with Dutch architect Janjaap Ruijssenaars to print a “Mobius ringâ€-like building for the 3D printing competition in Europe, which is a 3D printed concrete technology. Bold practice in the construction industry. Recently, a group of 3D printed houses appeared in Qingpu, Shanghai. The developer, Ma Yi, used recycled construction waste and fiberglass as printing materials, and completed 10 200-square-meter buildings in 24 hours using self-designed assembly printing machinery. Printing, but the material and structural strength and durability of the materials used are still worth considering.
A former Dutch construction company has also started printing a building, which is mainly done by printing the prefabricated parts printed on the 3D printer like building blocks. In the printing process of 3D printed concrete, it is the process of stacking layers of concrete strips. Inevitably, step effects appear on the surface of the printing member, and the surface is rough and uneven, which not only affects the appearance, but also may lead to errors in accuracy. It can be clearly seen in Fig. 6 that there are lateral stripes on the surface of the printed component, the level is relatively obvious, and the surface flatness needs to be beautified. In order to deal with such problems, two methods are generally used: one is to reduce the diameter of the printing nozzle and reduce the height of the step. This method will reduce the printing speed, affect the construction efficiency, and can not guarantee the ideal flatness of the surface; The second is to carry out subsequent screeding after molding, which requires repeated work, which is time consuming and laborious. In order to solve these problems in the construction of 3D printed buildings, Professor Behrokh Khoshnevis of the University of Southern California proposed ContourCrafting. The contour building process is a process of building construction using 3D printing technology, including the contour printing system (Extrusionsystem) and the internal filling system (Fillingsystem). The principle is to print the outer contour first, then fill the interior with the material to form Concrete member.
The biggest feature of the contour building process is that a trowel is added to the nozzle. The trowel ensures that the surface of the building can be flattened while the building is being printed, which is a good solution to the problem of uneven surface of the 3D printing surface. In addition, the contour building process can realize the reinforcement of concrete members while 3D printing the building, and further try the printing construction of high-rise buildings. Based on 3D printing technology, the contour building process with trowel has many advantages. On the one hand, the surface of the building is flattened while printing, which improves the smoothness and precision of the printed building surface and avoids repeated construction. It is also possible to increase the thickness of each layer of printing and improve the building efficiency of the building. It can print a 2,500 square foot house within 24 hours. In addition, the presence of a filling system in the print design allows for the filling of internal materials as needed, which greatly improves the structural performance of the printed building.
3.3D printing concrete problems
The current 3D printed concrete technology is in the stage of research and development, and its performance and application are in the exploration stage. Therefore, there will inevitably be some problems.
(1) Problems with raw materials. 3D printed concrete is more demanding than conventional molded concrete. The ordinary cement may not meet the requirements of building performance and printing technology at the same time. The quality requirements of coarse and fine aggregates will be higher, and even a new crushing process system should be adopted. However, the role and mechanism of action of the admixture in the concrete system may also change.
(2) The problem of the ratio theory. 3D printing concrete technology puts special requirements on the new mixing properties such as cohesiveness, extrudability and buildability of concrete. At the same time, the printing process will have a great influence on the post-hardening performance of concrete. This is not simply It can be satisfied according to the adjustment of parameters such as water-cement ratio and sand ratio. Whether the concrete prepared according to the existing concrete mix ratio theory can satisfactorily meet the working requirements of 3D printing, and the requirements for the mechanical properties and durability indexes after printing hardening have yet to be determined, which requires a new perspective to propose new ones. Theory to better adapt to 3D printed concrete technology.
(3) Problems with the software. Different from traditional concrete construction, 3D printed concrete needs to complete the construction of the model on the computer and then convert it into physical objects through the automatic program. Therefore, the design software becomes an important part of the preparation stage of 3D printed concrete technology, and how to implement the software. The transition between reality and reality becomes an indispensable step in the development of printed concrete.
(4) The problem of molding height. The current mechanical capabilities of 3D printed concrete technology are still in the stage of flat expansion, which can be applied to the construction of low-rise large-area buildings. For high-rise buildings that are widely used, printing is not possible. Only by printing pre-forms and then assembling them. The way to achieve this, at the same time, to print out dozens of buildings, you need to design a huge 3D printer to solve the structural problems of large buildings, as well as the printing problems of steel bars in buildings. In addition, 3D printed concrete will have great changes in production processes and safety measures, which will cause more or less problems, which are subject to further research and discovery.
3D printed concrete outlook
With the development of science and technology, fewer and fewer people are willing to engage in front-line manual labor. As a labor-intensive concrete construction industry, there will be a huge challenge. The emergence of 3D printing concrete technology combined with 3D printing technology is undoubtedly one. The great gospel has a very broad prospect for development. The 3D printing concrete technology eliminates the cumbersome procedure of demoulding demoulding during the construction process, which greatly simplifies the construction process, so that the construction rate can be increased by more than 10 times, and the concrete can be fully utilized to reduce the cement. The use of the building can improve the service life of the building, reduce the generation of construction waste, and reduce the redundant construction. At the same time, the 3D printing machine only needs the control of several technicians, which reduces the number of construction workers and is in line with the development of today's society. trend. In addition, 3D printed concrete technology can realize the printing of various shapes of buildings, and has less requirements on the environment. It can be applied to the exploration of outer space and quickly complete the construction of space base.
At present, 3D printing concrete technology is in the initial stage of development. In order to realize the universal application of 3D printing concrete technology, it is necessary to solve key problems for its existing problems. The research and development of future 3D printed concrete technology can be carried out as follows:
(1) Research on concrete materials. Although TTLe et al. of Loughborough University in the United Kingdom conducted a partial study on 3D printed concrete, it proposed some performances required for 3D printed concrete, but mainly based on the preliminary understanding of 3D printed concrete technology at the present stage, lacking relatively systematic, Theory, in-depth research. In order to make 3D printing concrete technology develop rapidly, it is necessary to carry out systematic and in-depth study on the raw material and preparation theory of concrete. Therefore, the new concrete mix ratio theory and new raw material requirements need to be improved according to performance requirements. It will be the main research topic in the development of 3D printed concrete technology.
(2) Research on supporting hardware and software. 3D printing concrete technology is a process of cooperation between computer software and printing machinery. How to transform the 3D model in the computer into a physical object through a software-controlled printing device, better combine with the automation process and achieve the best results. This will be a long-term process.
(3) Research on printing process. How to reasonably arrange the order of printing and control the all-round climb of the print head are important factors in determining printing efficiency, and also need to pay attention to in future research. At the same time, the current printing height of the 3D architectural printing process is greatly limited, and the development of society has gradually led to the development of concrete buildings. This requires a new printing process to achieve high-level printing and high-level development. Structural strength.
Comprehensive analysis of 3D printed concrete technology will become a new direction for the development of the industry
Concrete materials are one of the most important civil engineering materials in today's society. They have made invaluable contributions to the development and construction of human society. With the development of social science and technology, high energy consumption and high pollution of concrete in production and application process. Such problems have gradually become prominent, which has become a major obstacle to the development of concrete materials. In order to meet the needs of sustainable development of the society, the performance of concrete itself is gradually developing towards high strength and high performance. At the same time, the emergence of new technologies has also provided a new direction for the sustainable development of concrete.
3D printed concrete technology
3D printing concrete technology is a new technology applied to concrete construction developed on the basis of 3D printing technology. Its main working principle is to pass the configured concrete slurry through the extrusion device under the control of 3D software, according to the preset. A good printing procedure, which is extruded by a nozzle, is printed to finally obtain a designed concrete member. 3D printing concrete technology is the latest concrete moldless molding technology in the printing process, without the need of the traditional concrete molding process. In 2012, researchers at Loughborough University in the UK developed a new type of concrete 3D printing technology. Under the control of computer software, the 3D printing machine uses a cement-based slurry material with highly controllable extrusion properties to accurately position the concrete panels and The printing of the holes in the wall enables the design of ultra-complex large-scale building components, opening a door for a unique concrete building.
1.3D printed concrete
With the advent of 3D printed concrete technology, ordinary concrete can no longer meet the needs of its technology, and further requirements are placed on the performance of concrete, which are reflected in the construction performance of fresh concrete and the mechanical properties and durability of hardened concrete. TTLe et al. at Loughborough University conducted related research. For fresh concrete slabs, specific performance requirements must be met to meet 3D printing requirements. The first is extrudability. In the 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 particles in the slurry is determined by the size of the nozzle opening, and strict control is required to eliminate The appearance of large particle aggregates will not be blocked during the printing process to ensure the smooth extrusion of the slurry.
Secondly, the concrete slurry should have good cohesiveness. On the one hand, better cohesiveness can ensure that the concrete will not break due to the performance of the slurry during the extrusion process through the nozzle, avoiding print omission. On the other hand, 3D printing is a final product obtained by layer-by-layer accumulation. Therefore, the combination between layers is a weak link of 3D printed concrete, which is an important factor affecting hardening performance, and better cohesiveness. The negative impact of the print layer can be minimized. Finally, the extrudability and cohesiveness ensure the performance of the previous printing and hardening, but it is difficult to ensure the smooth printing process. In the process of 3D concrete printing, it is necessary to keep the state of the printed portion intact, and there is no phenomenon that the printing is interrupted due to collapse or tilt, which places demands on the constructability of the concrete slurry.
3D printed concrete technology also has a large impact on the performance of hardened concrete. During the printing process, the concrete is extruded in strips, and the problem of bonding between the strips is an important factor in determining the structure of the hardened printed concrete. Poor cohesiveness can lead to large and large internal printing concrete structures. Porosity will also have a major impact on the durability of concrete; in terms of strength, the use of printing technology will result in the loss of concrete strength, resulting in the strength of printed concrete is lower than that of molded concrete of the same ratio, and printing will also The strength of concrete is characterized by anisotropy. The strength is determined by the direction of printing. In addition, the maintenance of water also has a great influence on the performance of printed concrete. This is also confirmed by other researchers. The reason is that the water conservation will have a certain improvement on the microstructure of the printed concrete, filling the voids caused by the printed concrete during the printing process, thereby improving the performance of the printed concrete.
2.3D printing concrete construction
As 3D printed concrete appears in the researcher's field of vision, 3D printed buildings are also produced. Italian researcher Enrico Dini invented the world's first large-scale 3D printer. The printer has hundreds of nozzles on the bottom that sprays magnesium paste. The sand is sprayed onto the adhesive to form a stone solid. The layers of the ground bond combine with the sand to form a stone building and successfully use the building materials to print a building 4 meters high. On this basis, he worked with Dutch architect Janjaap Ruijssenaars to print a “Mobius ringâ€-like building for the 3D printing competition in Europe, which is a 3D printed concrete technology. Bold practice in the construction industry. Recently, a group of 3D printed houses appeared in Qingpu, Shanghai. The developer, Ma Yi, used recycled construction waste and fiberglass as printing materials, and completed 10 200-square-meter buildings in 24 hours using self-designed assembly printing machinery. Printing, but the material and structural strength and durability of the materials used are still worth considering.
A former Dutch construction company has also started printing a building, which is mainly done by printing the prefabricated parts printed on the 3D printer like building blocks. In the printing process of 3D printed concrete, it is the process of stacking layers of concrete strips. Inevitably, step effects appear on the surface of the printing member, and the surface is rough and uneven, which not only affects the appearance, but also may lead to errors in accuracy. It can be clearly seen in Fig. 6 that there are lateral stripes on the surface of the printed component, the level is relatively obvious, and the surface flatness needs to be beautified. In order to deal with such problems, two methods are generally used: one is to reduce the diameter of the printing nozzle and reduce the height of the step. This method will reduce the printing speed, affect the construction efficiency, and can not guarantee the ideal flatness of the surface; The second is to carry out subsequent screeding after molding, which requires repeated work, which is time consuming and laborious. In order to solve these problems in the construction of 3D printed buildings, Professor Behrokh Khoshnevis of the University of Southern California proposed ContourCrafting. The contour building process is a process of building construction using 3D printing technology, including the contour printing system (Extrusionsystem) and the internal filling system (Fillingsystem). The principle is to print the outer contour first, then fill the interior with the material to form Concrete member.
The biggest feature of the contour building process is that a trowel is added to the nozzle. The trowel ensures that the surface of the building can be flattened while the building is being printed, which is a good solution to the problem of uneven surface of the 3D printing surface. In addition, the contour building process can realize the reinforcement of concrete members while 3D printing the building, and further try the printing construction of high-rise buildings. Based on 3D printing technology, the contour building process with trowel has many advantages. On the one hand, the surface of the building is flattened while printing, which improves the smoothness and precision of the printed building surface and avoids repeated construction. It is also possible to increase the thickness of each layer of printing and improve the building efficiency of the building. It can print a 2,500 square foot house within 24 hours. In addition, the presence of a filling system in the print design allows for the filling of internal materials as needed, which greatly improves the structural performance of the printed building.
3.3D printing concrete problems
The current 3D printed concrete technology is in the stage of research and development, and its performance and application are in the exploration stage. Therefore, there will inevitably be some problems.
(1) Problems with raw materials. 3D printed concrete is more demanding than conventional molded concrete. The ordinary cement may not meet the requirements of building performance and printing technology at the same time. The quality requirements of coarse and fine aggregates will be higher, and even a new crushing process system should be adopted. However, the role and mechanism of action of the admixture in the concrete system may also change.
(2) The problem of the ratio theory. 3D printing concrete technology puts special requirements on the new mixing properties such as cohesiveness, extrudability and buildability of concrete. At the same time, the printing process will have a great influence on the post-hardening performance of concrete. This is not simply It can be satisfied according to the adjustment of parameters such as water-cement ratio and sand ratio. Whether the concrete prepared according to the existing concrete mix ratio theory can satisfactorily meet the working requirements of 3D printing, and the requirements for the mechanical properties and durability indexes after printing hardening have yet to be determined, which requires a new perspective to propose new ones. Theory to better adapt to 3D printed concrete technology.
(3) Problems with the software. Different from traditional concrete construction, 3D printed concrete needs to complete the construction of the model on the computer and then convert it into physical objects through the automatic program. Therefore, the design software becomes an important part of the preparation stage of 3D printed concrete technology, and how to implement the software. The transition between reality and reality becomes an indispensable step in the development of printed concrete.
(4) The problem of molding height. The current mechanical capabilities of 3D printed concrete technology are still in the stage of flat expansion, which can be applied to the construction of low-rise large-area buildings. For high-rise buildings that are widely used, printing is not possible. Only by printing pre-forms and then assembling them. The way to achieve this, at the same time, to print out dozens of buildings, you need to design a huge 3D printer to solve the structural problems of large buildings, as well as the printing problems of steel bars in buildings. In addition, 3D printed concrete will have great changes in production processes and safety measures, which will cause more or less problems, which are subject to further research and discovery.
3D printed concrete outlook
With the development of science and technology, fewer and fewer people are willing to engage in front-line manual labor. As a labor-intensive concrete construction industry, there will be a huge challenge. The emergence of 3D printing concrete technology combined with 3D printing technology is undoubtedly one. The great gospel has a very broad prospect for development. The 3D printing concrete technology eliminates the cumbersome procedure of demoulding demoulding during the construction process, which greatly simplifies the construction process, so that the construction rate can be increased by more than 10 times, and the concrete can be fully utilized to reduce the cement. The use of the building can improve the service life of the building, reduce the generation of construction waste, and reduce the redundant construction. At the same time, the 3D printing machine only needs the control of several technicians, which reduces the number of construction workers and is in line with the development of today's society. trend. In addition, 3D printed concrete technology can realize the printing of various shapes of buildings, and has less requirements on the environment. It can be applied to the exploration of outer space and quickly complete the construction of space base.
At present, 3D printing concrete technology is in the initial stage of development. In order to realize the universal application of 3D printing concrete technology, it is necessary to solve key problems for its existing problems. The research and development of future 3D printed concrete technology can be carried out as follows:
(1) Research on concrete materials. Although TTLe et al. of Loughborough University in the United Kingdom conducted a partial study on 3D printed concrete, it proposed some performances required for 3D printed concrete, but mainly based on the preliminary understanding of 3D printed concrete technology at the present stage, lacking relatively systematic, Theory, in-depth research. In order to make 3D printing concrete technology develop rapidly, it is necessary to carry out systematic and in-depth study on the raw material and preparation theory of concrete. Therefore, the new concrete mix ratio theory and new raw material requirements need to be improved according to performance requirements. It will be the main research topic in the development of 3D printed concrete technology.
(2) Research on supporting hardware and software. 3D printing concrete technology is a process of cooperation between computer software and printing machinery. How to transform the 3D model in the computer into a physical object through a software-controlled printing device, better combine with the automation process and achieve the best results. This will be a long-term process.
(3) Research on printing process. How to reasonably arrange the order of printing and control the all-round climb of the print head are important factors in determining printing efficiency, and also need to pay attention to in future research. At the same time, the current printing height of the 3D architectural printing process is greatly limited, and the development of society has gradually led to the development of concrete buildings. This requires a new printing process to achieve high-level printing and high-level development. Structural strength.
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