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3D concrete printing took the construction industry by storm, when it first arrived at the scene more than a decade ago. Back then, Dr. Behrokh Khoshnevis of the University of Southern California came up with contour crafting; a layered fabrication technology. It uses a computer-controlled gantry to support the automated extrusion of a cement-based material to build structures. It is referred to as the first-generation of 3D printing methods. Ever since, there has been a rise in the number of businesses that offer 3d printing as additive manufacturing, while expanding the scope of the process.
Powder 3D printing became a popular technology. Under this, powdered materials are melted and sintered together through laser exposure to form a layer. Once this layer has solidified, another layer is similarly created above it and the process continues till the desired 3D model is fabricated. The powder bed fusion is where a thermal energy is used to sinter powdered particles to create the desired structure. It comes particularly handy for ducting and complex pipe assemblies. Alternatively, there is binder jetting, a process which uses a liquid bonding agent instead, to agglutinate the specified regions of a powder bed. It is commonly used to fabricate sand casting and functional metal parts. However, the latter inspired the pioneering D-Shape technology. D-Shape, invented by Italian Architect Enrico Dini, is a particle bed process, that alternates a layer of granular material with a suitable ‘ink binder’, which coagulates into the preferred shape. It is best suited for off-site prefabrications, especially for complex construction elements.
With the progress of such automated construction machinery, many benefits were said to be realized; the first being resource optimization. With traditional construction, there is a dual downside of ordering concrete in excess quantities and building the supporting formwork to bear the load during casting. 3D printing technologies can overcome these, by replacing cement which a great deal of energy to more sustainable alternatives. Additionally, it nurtures architectural creativity. Without the need for costly customized formwork, designs can take a free form and even mimic organic geometries. 3D concrete printing can significantly shrink project timelines along with error reduction. Such automation developments can reduce fatalities on job site, while ensuring reduced carbon footprint of the project. Take for instance, the Striatus Bridge established by ETH Zurich, in collaboration with Zaha Hadid Architects and Incremental3D, among others. This arched bridge was installed in Venice for the International Architecture Exhibition. A new printing process was employed wherein instead horizontal concrete layers, the concrete ink (developed by Holcim) was applied in a direction orthogonal to the flow of compression forces. This pedestrian bridge is composed of blocks which can be assembled to form the mobile structure. And should the bridge not be required, it can be recycled.
Despite all the buzz around printing, there has been considerable debate on whether this is a technology to stay or a trend to shrivel. This segment of additive manufacturing is yet to build a fully functional building. Take for instance one of the most famous 3D printed spaces - the Office of the Future in Dubai. Designed by the architectural firm Gensler, this office building was printed by the Chinese company Winsun, using a special cement mixture. The 17-day turnaround project may have required only one personnel to monitor the printing process at any given time, however it was supplemented by the workforce required for installing building components. Additional advanced computers were also used in order to conducted quality checks. It appears that 3D printing in construction manifests more as a decorative technique, that can offer shelter with minimal functionality.
The fundamental process of concrete printing involves extrusion of a composition, layer by layer. This is achieved through a printhead, supported on a construction frame or with delta devices (where the printhead suspended upon levers which are attached to vertical guides). Even so, the composition used is not standardized. Each business prepares their own mixture based on their printer and its nozzle, as well as the requirements of the finished product, in terms of durability, and ductility.
3D printing is yet to address quality control concerns, efficiently. This presents two cases. Firstly, let’s look at the procedure, say powder bed fusion technologies. Laser-based additive manufacturing workflow can affect the configuration of 3D printed parts. Since there are many variables affecting the final outcome; a trial and error method can eliminate unwanted deviations, which is not an efficient process.
While 3D printing claims to require a smaller pool of labor, this is not an accurate picture. In the construction industry, labor shortages arise on account of demand for skilled personnel. Considering this existing problem, with 3D printing, finding qualified workers becomes a more difficult task.
Perhaps one way to inspire collective effort to address the above three, is through drafting coherent rules and regulation. After all, considering how different business approach this niche market, there need to be proper guidelines, especially in terms of liability. Ascertaining whether the accountability for a defect in the structure falls on the developers using the technology or the contractors owning the printing machines. Ambiguity hinders adoption, and this hold true for any innovation, particularly with respect to the construction industry.
While there is much left to be strategically aligned for the successful implementation of 3D printing in construction, its value addition in terms of cost savings, and shorter project schedules to the industry cannot be denied. Overall, research would need to investigate how the different elements which cannot printed, can be incorporated into a building project.
