Dec 4, 2017 | By David

As concrete 3D printing continues to revolutionize construction projects all over the world and change the way people think about architecture, many companies and research institutions are putting a lot of effort into continuing research in this field, hoping to advance the technology and discover new ways that it can be implemented. The most recent developments have come from the Technical University of Munich, where researchers have been experimenting with a number of different concrete AM processes, the most promising of which is the relatively new '‘selective binding'’ approach.

These research activities are being conducted in a collaborative effort between the TUM’s Chair of Timber Stuctures and Building Construction and the Centre for Building Materials. The German Research Foundation (DFG), along with the German Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) research initiative "Zukunft Bau", provided the funding to support these ongoing research projects, some of which have just recently been launched.

The main advantage that 3D printing offers for construction is improved freedom of design, as well as the increased ease and speed with which prototypes can be put together. As opposed to using formworks and molds, 3D printing processes can create concrete structures by selectively depositing material exactly where it needs to go, which then will solidify in place. This allows for much more complex shapes to be made, which would be impossible with conventional techniques, and these more intricate structures allows for improved properties. For example, a concrete pipe could be made with much thinner walls due to its being supported by an elaborate internal bracing structure, which saves on materials as well as reducing weight without sacrificing strength.

The most common concrete AM technique used has been the standard extrusion method, which extrudes pre-made concrete from a nozzle, similar to how FDM 3D printing creates structures from thermoplastics. Selective binding is a newer method, which extrudes a mixture of water and cement instead of concrete. The build area is primed with layers of sand, and they will gradually set to form concrete shapes after being doused with the extruded material. The excess sand is then removed.

The TUM team had to build a selective binding unit in order to test out this latter concrete additive manufacturing process, which took around three years to perfect. Their over-dimensioned 3D printer fills an entire laboratory room in the basement at their premises. Before initiating the 3D printer, sand is first distributed using an automatic scattering system. A three-dimensional system of tracks moves the print head around, allowing it to be positioned at any specific point in the working space, as required by the project. The nozzle can then apply fluid exactly where it needs to go.

Successful printing depended on getting the right thickness of the layers, the right grain size of the sand, an appropriate speed for the print head to move at, and the right type of nozzle, amongst other things. Engineers from the TUM Centre for Building Materials helped out with optimizing the printing parameters. The team is now developing a 3D printer whose print head will be equipped with several thousand nozzles. which will make it possible to manufacture components with volumes of approximately ten cubic meters, the height of a storey in a building. This will be the first time parts of this size have been made using this selective binding technique, and tests should start next year.

The team also made some advances with the more common extrusion 3D printing method, in terms of the materials used and the system adopted to process them. One project saw wood chips being added to the standard concrete mix, which can provide integrated thermal insulation due to the extra air in the material, protecting buildings from undercooling in the winter or overheating in the summer. This lightweight wood-concrete is just as resilient and insulating as conventional gas-aerated concrete, but its printability means that it can be made into much more elaborate structures. A newly designed computer-controlled robotic arm was used to move the print head and extrude this new material more efficiently, precisely placing the concrete strands on top of one another in order to form the desired structure.

According to Dr. Klaudius Henke of the TUM Chair of Timber Structures and Building Construction,  "Additive manufacturing is extremely attractive for construction: It enables a wide range of shapes at high levels of cost-efficiency, even in small batch sizes... (It) will change architecture. The technology not only allows more versatile shaping, but also more variety, since each component can be individually designed without incurring any additional costs."

 

 

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Nissim Hasson M. S., M. ASCE, Civil Engineer wrote at 12/6/2017 12:56:58 AM:

It is a great innovation to use these 3D printers to make suchs a beautiful concrete work. Plese, receive my congratulations.

Salvatore J. Monte wrote at 12/5/2017 9:08:34 PM:

Read your 3-D concrete article with interest. We can surface modify the Portland cement surface with 1.5-nanometer organometallics by a patent-filed process to increase the Portland cement reaction with water and reduce the water to cement ratio by one-third or increase the flow (decrease the slump) by making the mortar "more wettable", thus facilitating 3-D processing. The surface modification also makes the mortar more compatible with polymerics and improves bonding and anti-corrosion performance to steel reinforcements. Salvatore J. Monte P.E., B.C.E., M.S.-Polymeric Materials, Fellow (SPE) BOG PIA President Kenrich Petrochemicals, Inc.



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