Recent articles on 3D printing in construction have sparked heated debate. This conversation was sparked by an article about the potential benefits of concrete 3D printing. The co-author of this article is Mustafa Batikha, assistant professor at Heriot-Watt University.
Published last year, the study found that if a two-story structure built of precast concrete in the United Arab Emirates had been 3D printed using a three-sheet printed cavity wall, the material costs of the entrepreneurs would have actually increased by 44%.
This was mainly due to the expensive concrete needed for construction, as it was felt that the proposed 3D printing method would be cheaper to implement. Contrary to the oft-cited green benefits of the technology, the paper also showed that its adoption would yield only marginal sustainability gains.
Since then, companies like COBOD, Apis Cor, and Black Buffalo 3D have challenged concrete 3D printing paper, particularly the practicality of the simulated construction on which its findings are based. However, Batikha has now reached out to the 3D printing industry with the following article, to explain how he came to his conclusions, and his intention not to suggest that “academia and industry are moving in any directions different”.
“I prefer not to respond directly to every review, but I have made recommendations for the industry. If they don’t take them, I don’t think concrete 3D printing will catch on in the future,” begins Batikha “I sincerely believe that academia and industry must work together to support the benefits of 3DCP technology.”
Concrete 3D Printing: Recommendations for the 3D Printing Industry
By Mustafa Batikha, Assistant Professor, Heriot-Watt University.
3D concrete printing (3DCP) has attracted considerable attention in the construction industry due to its ability to shape concrete in a way that allows it to meet architectural geometric requirements without formwork. As a result, some countries, such as the United Arab Emirates, have placed 3DCP at the heart of their strategic plan for future construction. However, the implementation of 3DCP in buildings is still modest.
Our research, conducted by Heriot-Watt University, B3G Engineering, and Equipment Boni, resulted in an article that shows how 3DCP offers advantages such as low cost, durability, and time savings over four other techniques. of current construction (as can be seen below). This is in addition to the great health and safety improvements that 3DCP could also bring to the construction site.
However, 3DCP also faces many challenges. In terms of material formulation, concrete mixes must meet certain criteria for fluidity, extrudability, buildability and compressive strength, as well as stability in the fresh concrete stage. In addition, the type of printer, whether it is a gantry beam or a robotic arm, plays a vital role in choosing the ingredients of the expanded concrete mix.
Printing speed is also a key parameter when designing a concrete mix, whereas off-site printing requires a mix that is not the same as in-site printing cases. This results in noticeable variability in mixes used in both research and practical applications, but the proportion of cement in stamped concrete is still high, hampering sustainability efforts.
Although the use of supplemental cementitious materials (SCMs) to replace this cement may be a solution, this procedure will no longer be viable for widespread use, as expected for 3DCP, due to the sheer limitation of SCMs compared to the industry demand. Research also suggests the need to start investing in calcined clay and limestone powder filler to replace cement as they are widely available.
System and normalization issues
Currently, adding steel reinforcement to printed structural elements is common practice, as building authorities do not have specific standards to validate the design of an unreinforced 3DCP structure. Additionally, when steel rebars are used, it ruins the advantages of 3DCP as a cheaper, faster, safer and more durable construction technique.
In a practical example, BESIX successfully printed an unreinforced halfway house in Abu Dhabi, but building authorities still refuse to encourage this practice, until a design standard has been put in place.
Another aspect of this is the configuration of the walls, as their printed shape must be optimized to reduce material waste and moderate the temperature inside the building. The use of a two-sheet cavity wall is a common practice in the printing market, which results in reduced use of printed concrete and several advantages for 3DCP, as shown in one of our studies .
During another study, we discovered that it was possible to integrate a printed cavity wall with three leaves in a building to maintain its internal temperature, at a monetary cost and CO2 emission similar to prefabricated construction. , but with a delay reduced by 34%. Going forward, the role of the geometric shape of a wall in ensuring the benefits of 3DCP should be an area of great interest for researchers.
Although off-site printing is the preferred choice for 3DCP companies to ensure print quality, the time and cost invested in transporting, mounting and assembling printed items on-site is considerable. On-site printing is ideal for mass deployment of 3DCP in buildings. This brings us back to the first question about the design of the material and the type of printer needed to do the construction on site.
System format plays a crucial role in build quality and mix design. A robotic arm printer may be more suitable for obtaining a precise architectural shape, such as a facade or a small building. In contrast, in large built-up areas, a gantry beam printer may be more efficient, as its system has lower operating and maintenance costs and is easier to use. Using a robotic arm is estimated to double the construction cost, so future building 3D printers could be in gantry beam machines.
Advancing 3D printing in construction
Going forward, the challenge is how to print parts under flex (e.g. slabs) with minimal steel reinforcement. As for multi-story buildings, even though companies like Winsun have already announced 3D printing of a five-story building, most printed houses are still one or two-story buildings. I think the future of 3DCP will focus on being able to build them in different loading scenarios, for example under gravity, wind or seismic conditions.
The researchers’ findings are detailed in their articles. The first was called “3D Printing of Concrete for Building Sustainable and Affordable Housing – Comparative Study», and co-written by Mustafa Batikha and Moiz Ul Fazal.
The second was titled “3D Printing in Concrete for Sustainable and Economical Construction: A Comparative Study”, and co-authored by Mustafa Batikha, Rahul Jotangia, Mohamad Yasser Baaj and Ibrahim Mousleh.
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Featured image shows COBOD’s BOD2 3D printer creating the world’s “first” 3D printed home extension. Photo via PERI AG.