In the year of 1984 the American Charles Hull invented the first 3D printer based on a vat photopolymerization technique called ‘stereolithography’ and thereafter he founded the 3D Systems. (24) Since then 3D printing has become one of the fastest growing technologies. Back in time this technology was very expensive. Year after year, 3D printing technology started to be present and more common in everyday life and printers became typically used in all types of industry fields, such as automotive, medicine, manufacturing, aerospace and construction. Because of the open source system, prototyping of new product and innovative applications of 3D printing in numerous fields are accessible for everyone.
In the last decades, there has been significant progress in the 3D printing in construction industry. 3D printing in construction can be mentioned to numerous printing technologies used to manufacture architectural or construction components. Even though the use of 3D printing in concrete is still at an early stage, various projects, conducted by government agencies, industry and academia, although gradually and carefully, have been developed in order to adapt the latest 3D printing technologies worldwide.
An amount of distinct approaches and techniques have been tried as well as off-site and on-site fabrication of construction components making use of gantry systems, industrial robots and tethered autonomous vehicles.
The automation of work in the construction industry looks more feasible and realistic in the very near future, owing to the fact of the technological advancement in nowadays’ world and observable progress in manufacturing techniques, commonly known as 3D printing. Some think that 3D printing in concrete besides being an innovation of advanced technology, it has the potential to alter dramatically the construction industry, in view of the fact that the use of this technology could lead to construction costs reduction, permit construction in more remote locations, more flexible designs and reduction in construction time as well. Furthermore, it provides some new sustainable benefits that a conventional construction method does not offer.
According to studies, in case automated 3D printing technology is further developed to a point where current conventional construction methods are less efficient than the additive manufacturing technology, then manpower requirements and construction materials may be considerably reduced.
Many projects involving 3D printing in construction are applied in the manufacturing of houses, sculptures, small bridges, structural components, artificial reefs, etc. For instance, in the United Kingdom a research team worked on developing computer-controlled 3D concrete printers that would permit curved and geometrically complex concrete designs. They were developed and designed in a way that the concrete could be directly applicable to the building site without any additional formworks. During the experiments driven by Loughborough University, robotic arms were utilized to print concrete structures in different and many curved shapes. Meanwhile, in China, researches are experimenting to build entire structure using 3D printed concrete structural elements.
One interesting point is that 3D printing technologies have advanced more and more, in a way that concrete can be printed around rebar installed prior to printing, this allows the printed concrete to be strengthened with reinforcement, just like it happens in the conventional construction methods.
Many types of 3D printing techniques are used at construction scale, suchlike powder bonding, material extrusion, and additive welding. Contour Crafting is a 3D printing technology which has obtained more popularity in science and engineering communities for the fact that it permits for rapid prototyping, creation of multi-material composites, manufacturing of complex geometries, and product customization as well. Contour Crafting is based in extrusion, and it provided the possibility of having smooth surface finish over accumulated successive thick layers by depositing wet concrete through a nozzle and against a side sharping trowel.
Several engineers anticipate a wonderful future for 3D printing in construction and few industry experts think that this technology may lead to a new industrial revolution.
While the use of Contour crafting and additive manufacturing in earthly applications looks optimistic, there is still a lot more to be explored and other critical challenges for extraterrestrial applications, just like construction in a low atmosphere as well as under reduced gravity. Even though these challenges are still to be beat, it is in fact expected that researches related to it will move forward and it may provide the solution for extraterrestrial shelter and protective hangers for equipment. Furthermore, it is assumed that new possibilities for space mission architectures and space exploration will continue to arise.
Generally, potential advantages of 3D concrete printing involve lower labor costs, better integration of function, faster construction, increased complexity and accuracy, and use of recycled materials, therefore producing less waste. (25)
This paper presents 3D printing techniques applied in the construction industry and its comparison with the conventional construction methods. Furthermore, a SWOT Analysis for both methods were developed in order to better understand their strengths, weaknesses, opportunities and threats. Moreover, main materials used in both methods were described and analyzed along this research paper.
2. 3D printer
2.1. 3DCP (3D Construction Printing)
Additive manufacturing (AM) known as well for different references such as three-dimensional printing (3D printing), rapid prototyping (RP), layered manufacturing (LM), is a different manufacturing process from the traditional methods, which is executed by integrating computer-aided design (CAD), material science and computer programming techniques as well, in order to produce physical prototypes from CAD models layer-by-layer.
Not long-ago AM has become welcome in the construction industry. In fact, there are three major printing ways used in the construction field. They are AM D-shape, concrete printing and contour crafting which will be discussed in more details in this document. (7)
These three major types of additive manufacturing share some sameness. Firstly, contour crafting and concrete printing are both based in material extrusion. In one hand concrete printing is accomplished with the help from cement-based paste, on the other hand contour crafting uses cement mortar.
Secondly, concrete printing needs to use another second material in order to support the created overhangs and other freeform features as well. The D-shape and contour crafting use single material but apply dissimilar methods to build different products. Thirdly, these three types of AM share a same characteristic, which is all of them are layered process that build the product layer upon layer. (7)
The research on printing methods for construction has recently increased and the reason for that is the opportunities which AM offers, suchlike the chance of producing geometrically complex structures, the variance in materials according to the need and its functions, and from a digital model, automate the construction process. Once all AM processes are modeled adequately during the planning phase, then those opportunities mentioned above can be exploited. (8)
For the construction scale, there are many types of 3D printing methods, which includes: extrusion (concrete/cement, foam, wax and polymers), additive welding, powder bonding (reactive bond, sintering, polymer bond). The application of 3D printing in construction will be seen in commercial, private and public sectors, by the reason of providing low labor costs, faster construction, less waste produced, more accuracy in complex designs and greater integration of functions. (14)
The fabrication of buildings and construction components (structural panels, columns and cladding) can occur either on-site and/or off-site, utilizing gantry systems and industrial robots. Heretofore, civil infrastructures, bridges, construction components and sculptures have been printed by use of 3D printing technology. (14)
The Fig. 2 shows the first 3D printed bridge in Madrid, Spain. The bridge spans 12 m and measures 1.75 m wide. It was made of fused concrete powder micro-reinforced with thermoplastic polypropylene. (15)
In the following picture Fig. 3, it is the first on-site 3D printed house made of concrete in Russia. It is a 38 square meters house, made of concrete and one single floor with an atypical design, exactly to show the flexibility of the building process. The building was totally printed on-site, rather than assembled from reprinted panels. The printer for this house could only print the self-supporting walls of the house, no floors, no windows and no roofs. The costs to print the house was 275 dollar per square meter, totalizing in an amount of 10.134 dollars. (16)
There was a discussion about not being feasible to build medium or large-scale models or high buildings by using 3D printing technologies, because of the size of 3D printers. Nevertheless, many significant improvements in developing large-scale 3D printers in order to meet the needs of industrial scale 3D printing, has occurred. One of the major developments on the utilization of 3D printing for printing an entire building, was developed in China. (9) A construction company called WinSun Decoration Design Engineering Co from Shanghai built in 2014 the highest 3D printed building. To make this possible they used a 6.6 meters tall, 10 meters wide and around 40 meters long 3D printer. The machine used for this construction, prints layer by layer making use of an “ink” made from a mixture of steel, cement, fiberglass, hardening agents and recycled construction materials. According to the company, even though their 3D-printed walls are greatly lighter than normal concrete walls, their walls still have much higher strength and toughness. They also assure that the walls won’t crack, they have strong water-proofing and better air permeability and heat retention when compared with conventional concrete walls. (10)
Besides the size of the printer, the material was also a very important topic in 3D printing because the material should have basic attributes suchlike quick hardening so that it could be used in 3D printing. After many studies, it was found that the stability and strength of the printed products by using the current printing materials (like plaster) would not allow the construction of buildings and large-scale models. Despite that recently, many materials have been modified and demonstrated to be potent as high-strength printing materials. In case of considering using concrete as a printing material, it would need to have an admissible degree of extrudability in order to be extruded from the nozzle of the printer. Furthermore, the concrete should fasten together to build each layer and have enough buildability property to permit it to lay down properly, stay in position and be sufficiently rigid to hold up further layers without caving in. By altering bind quantities and the proportion of other admixtures in the mix design, they finally reached to the ideal concrete, strong enough to be used in high-rise residential or other large-scale building projects. (9)
The “Office of the Future” is a fantastic 3D printed building. It is the first one totally functional, inhabited and it was inaugurated on May 23, 2016. This 250 square meters building was printed offsite in a factory, shipped and subsequently assembled onsite. Merely 18 workers were part of the crew and surprisingly the total project period, from beginning of printing until the finished assemble took only 17 days for a total of $140,000 in construction and labor costs. (11)
It is important to mention that normally these homes are not totally printed on site, but indeed prefabricated in a factory and afterwards delivered on site where walls are settled onto pre poured slab foundations and strengthened with traditional steel reinforcement. Moreover, roofs, windows and doors are not printed, that means each wall is printed keeping the space where windows and doors will later be placed. (11)
Besides all of that, there is many advantages offered by using 3D printing technology to the construction industry. Labor efficiency, cost saving, time, design complexity and environmental/economic impacts, are the four main areas in which 3D printing can have the most notable effect. As an example, the graph below (Fig. 7), shows clearly the difference of costs of labor and the costs of raw material between the 3D printing technology and the conventional construction method.
As a matter of fact, the implementation of 3D printing in construction may improve the productivity. It has the possibility to decrease the number of workers on site, speed up the construction process and reduce risks during construction. (12)
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