Brief overview on 3D Construction Printing


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Contour Crafting

1. Introduction

Since about 1994, the construction sector generally faces an increasing productivity gap when compared with other classic manufacturing sectors like equipment manufacturing, the automotive or the aerospace industry. This gap has further increased meanwhile and many studies from well-reputed strategy and consultancy firms state this. Not all studies are identical, but the bottom line is.
In the author´s view, the reason for this increasing gap is the successful and ongoing implementation of the principles of standardization, industrialization, automation and – increasingly – digitalization by firms that are active in the sectors of mechanical engineering, automotive and aerospace whereas the overall construction sector has ignored either these developments or simply hasn´t done its share yet. In addition, in current times of many break-throughs, new technologies combined with striking business models increasingly show disruptive effects in their markets. In other words, competitors from unexpected angles and industry newcomers with disruptive ideas now threaten major players in the traditional and monolithic sectors.
Finally, we have arrived at one of these new technologies. It generally can be addressed as 3D Construction Printing. It builds on the idea of layer-by-layer manufacturing, which is the unifying characteristic of all 3D printing technologies, regardless of materials involved. A significant number of reports, pictures, and articles can be found online with respect to construction 3D printing, some of which are very enticing and impressive at the first glance.
It should be mentioned that in this article the discussions are mainly provided from a business standpoint. As such, any new construction technology should be evaluated using current benchmarks in terms of construction time, construction cost, and quality. It is also important to note the total-cost-of-ownership mentality, which is prevailing the real estate and construction industry.
As soon as any “Wow effect” of new, even spectacular things like 3D Construction Printing, have vaporized, things pretty much tend to boil down to this very triangle of competitive time, cost, quality - and applicable building codes. All this can be very sobering. At different points of history, builders have adopted different construction methods, technologies, and materials. Buildings are made of either stones, bricks, timber, steel structures, poured concrete, concrete precast panels, or other materials or by other techniques. each newly emerged construction technique needs to challenge the conventional methods of construction. In other words, only business models are disruptive, technologies alone are never. If there is no economically striking effect, one typically speaks of “happy engineering”.

2. Technological market segmentation

From a general perspective, 3D construction printing has three very striking initial benefits. First, 3D printing is a digital process from the very beginning. No need to digitalize it, it is digital already. Job done. Second, complexity of design, within certain boundaries however, does not involve extra effort and hence it does not impose additional cost. Third, concrete 3D printing could be a fully automated process mainly monitored by one operator per shift. However, the devil is in the detail, and therefore, let´s have a look at these details.
First of all, let us have a look at all currently available technological approaches in this current niche domain and let´s try to derive technological market segments from this. From the author’s perspective, four segments could be identified in this space, which are governed by different and distinct rules. These four segments have been listed below in ascending order of technological complexity:
A. Construction Related Artwork
B. Shell Component Printing
C. Shell Printing
D. Contour Crafting

A. Construction Related Artwork: respective applications deal with either fancy building portals, free form structures, formwork or art objects of different forms and sizes in and around buildings that typically are not part of any load bearing building structure. To print this, the main approach is to use industrial robots from ABB, Kuka or other major players active in this domain. Then hoses and pipes are attached to the robots and customized programming is done for these ends. Printed materials are typically special mortars with no aggregates but chemical additives. Limitations of respective applications can be derived from sizes and dimensions of employed industrial robots, nature and cost of materials and respective product offerings. It is likely that some of these products will find their respective markets or niches to make a sustainable business out of it.

B. 3D Shell Component Printing: respective applications aim at building house shells by printing many individual and hollow wall objects, either on-site or off-site, stack or assemble them and then fill them up with poured concrete and finally finish the shell structure (also refer to chapter 3. Materials). Here again, in most cases industrial robots come into play, and, again special mortars serve as printed materials. Intentionally or unintentionally, this approach mimics the globally existing production of concrete precast panels. The difference, however, is that precast panels are solid functional walls already when they arrive at the jobsite. They consist of standard concrete and contain all required rebar, pipes and electrical pre-installations whereas their mortar printed counterparts lack all of this. Based on the available evidence, this approach cannot compete with well-established pre-fabrication facilities in terms of cost, time, and quality of produced components. In addition, it has to be clearly stated that these concepts only focus on house shells, which typically account for only 25 to 35% of the total construction cost of a building.

C. 3D Shell Printing: this approach aims at manufacturing house shells, rather than complete houses. Respective applications aim at printing house shells directly at the jobsite. Some intend to print the shell in one shot, so no repositioning of the printer is required. Some need repositioning of the printer in order to complete the printed shell structure. In other words, in this approach complete shell structures are printed, unlike the previous approach (B) in which only segments of the shell are printed. Companies that have adopted this approach either develop and use customized equipment, or they rely on a configuration of the off-the-shelf OEM products, which have been originally designed for other applications. To determine competitiveness, further key questions are:

  • What material is printed?
  • How quickly and easily can a printer be positioned or re- positioned by operators?
  • What is the system weight, handling time and effort?
  • How much personnel is required?
  • What is the time, cost and quality relation vs. local competition?

D. Contour Crafting: published in 1996 by Prof. Berok Khoshnevis, the concept of Contour Crafting aims at manufacturing of close to turnkey houses through a combination of 3D construction printing and automation. While the concrete shell is printed bottom up, all other building components like rebar, piping, wiring, electrical installations, tiles, floors, etc. except for doors and windows are automatically inserted or installed as the whole structure rises. Contour Crafting Corporation, headquartered in Los Angeles, headed by CEO Berok Khoshnevis, realizes the concept of Contour Crafting via two development steps: the first generation fully covers the first robotic function which is printing concrete house shells of up to 200 [m2] floorplan in one shot. The second generation will provide the full set of robotic functions. The first generation has been introduced at Bauma 2019 in Munich. The dynamically exhibited CC-108 proprietary gantry printer is light; the whole robot including delivery system weighs less than 1,000 [kg], and is easily positioned or repositioned by only two persons. In terms of iP, the company holds over 100 national and international patents and has won two prestigious NASA awards.

3. Materials

For 3D construction printing applications aiming at printing load bearing structures (buildings), one first key matter is materials. The printed materials, to be precise. In the internet, 3D construction printing seems to be synonymous with concrete 3D printing. Almost everyone on the net claims to print concrete.
Why? Because everybody, including authorities, knows and trusts concrete. Concrete is everywhere. It is a technically proven, lasting, globally available and relatively inexpensive material. These three factors matter a lot in a high volume business like construction. However, in most cases, the reality is that printed materials are rather expensive toothpaste-like cementitious materials and not standard concretes. Special mixtures with either no aggregates or aggregates smaller than 4 mm in grain size. Why is this important? Four reasons: first, there is the price component as already mentioned above. A high volume business like construction cannot afford using materials that are more expensive as a substitute for an inexpensive and proven material. Second, the effect of adding gravel makes it possible to reduce the cement content, which improves dimensional stability of the printed material and all this reduces the risk of shrinkage cracking. If there are no aggregates, there is no such effect. Third, these special mixtures have different material and elastic properties than standard concretes. As in many cases, the printed wall parts are intended to serve as lost formwork, the wall cores are then filled up with standard concretes.
Due to the significantly different material properties, these two materials do not form a monolithic structure and hence the structural performance of the final structure is affected. Therefore, the printed special mixture structures are typically statically, economically as well as ecologically lost. So why print with mortars in the first place? I assume it´s not primarily an intended ingenuity to do so but it´s simply the easiest way as it is extremely difficult to print with standard concretes. The first main obstacle is sound processing of concrete with regular aggregate sizes in combination with a highly precise digital layer printing process vs. a splish-splash concrete pump being in use to fill up formwork. The challenges are beyond any comparison. Therefore, there is not a single off-the-shelf component available for such a 3D printing process that has intentionally been designed for such ends and hence it´s a time-consuming, demanding and costly R&D process for any 3D Construction Printing firm to design, test and approve of such mechanical components for such very applications. Naturally, it is much faster, easier and cheaper to use available industrial robots, special mortars and a tube as "nozzle" to deposit the material but this approach has its limitations.

4. Productivity

The second key matter is productivity of the printing process. This is related to the printing speed and dimensions as well as characteristics of printed layers. Low-tech solutions show printing materials exiting from a simple tube or hose. The result is a very high number of relatively narrow and wide layers following a given path. Also, there is a certain finishing effort to be performed. High-tech solutions show sophisticated and often proprietary printing nozzles, which not only master a ratio of layer height to width close to 1 but also print a given wall type in one path. Such wall types are typically either solid walls, hollow walls or connected inner and other wall parts which can be filled with concrete of the same type, insulation materials or other matching materials. Apart from the productivity of the printing process itself, it is equally important for overall productivity whether components or whole structures are printed and whether this is done on-site or off-site.

5. Regulatory obstacles

Globally, building authorities rely on regional or national building codes in their permitting process for constructions. As of now, 3D construction printing generally is not part of any regular building code as it is a recent technological concept. Therefore, objects or structures that have been printed in the public so far, needed to have some relation to a university project or have another kind of preliminary or experimental status. What complicates things further is that there are many different technological approaches in this domain and different groups for different applications have used many different proven and unproven materials. As long as a 3D construction printing firm is unable to get a permit in a regular permitting process, there won´t be a market and hence the foundation for any regular business is missing. In order to resolve this crucial issue, the Contour Crafting Corporation (USA) has started a cooperation with the International Code Council (ICC) in January 2019. This collaboration resulted in preparation of a document on acceptance criteria for 3D construction printing using Contour Crafting technology (AC509). On June 4th 2019, a committee of building officials reviewed AC509 and unanimously approved this new acceptance criteria document. AC509 will be followed by an Evaluation Report (ESR) that will serve as a basis for establishing an internationally recognized permitting process for automated construction using Contour Crafting technology.

6. General outlook

In summary, the author believes that only some of the current ongoing approaches with respect to construction 3D printing will survive and will be adopted as economically viable construction methods. In general, however, the author anticipates that the construction 3D printing market share will considerably grow in the near future. The adoption of construction 3D printing will mainly be in the residential and commercial building sectors.

Published in The Indian Concrete Journal,
Volume 94, Number 8, August 2020

Werner Heinz Bittner

Werner Heinz Bittner

Master of Mechanical and Industrial Engineering, Technical University of Vienna, is a Chief Executive Officer of Umdasch Group Ventures GmbH (Austria) and Chairman of the Board of Directors of Contour Crafting Corporation (USA). He has held senior leadership positions
in various organisations in different industries like surface engineering, graphic arts and pharmaceutical manufacturing.

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