I have decided to investigate the mix design and structural properties of the various methods of 3D printing concrete. I chose this topic because I was intrigued by the shapes that can be made by this process but wondered if the pieces would have only architectural value. If the printed members can or will be able to in the future be a part of the structural system of a building, the ability to use the process in Intelligent Building practices would expand greatly. If the process can form members of suitable strength, it would be possible to sketch shapes in a BIM program and have them printed. The 3D shapes are simply sliced into layers and the filled area of each layer is communicated to the printer. Spaces could be left open for utilities to pass through, which could prevent further costs for drilling into the members later, etc.
In the past, the systems available for forming concrete are formwork (either cast-in-place or factory fabricated), "self-compacting" (which uses superplasticizers and still requires vibration), and sprayed concrete (which requires a backing material). 3D printed concrete would be able to be made without vibration or any sort of formwork or backing, which could reduce costs. However, this has not necessarily made it immediately the best option.
The major problem with this investigation is that the process still varies quite a bit, with some forms of 3D Printing using direct extrusion and others using sprayed powders. In extrusion, the most important properties for the wet concrete are the "flowability," the ability of the concrete to be pushed through the printer and form consistent filaments, and "buildability," which is required so that the mix will be rigid enough to stay in the planes and not sag while also being able to bond to the layers above.
For the sprayed powder process, the geometry may be better defined, as the layers would be much thinner. It surprised me that this type is so much less explored, but this may be because it can be considered too closely related to shotcrete. In addition, it is difficult to ensure that the water is incorporated in the powder, especially if a low water content mix is wanted.
Another complication is that 3D printed concrete is an anisotropic material because of the way it is made. Bonding between any extruded tubes and between layers has a great effect on the cured properties of the concrete. This bonding variability can increase based on the time required for formation, so larger pieces are very likely to have poor performance in shear along these planes or in tension pulling planes apart.
These points will be the major discussions to be addressed in my paper, along with the results of current testing and the future outlook for when and how 3D printing could form suitable structural concrete members. For example, I have yet to find any references to experimenting with any reinforcement other than small fiber reinforcement, and was wondering if there is any research into how a printer could perhaps print around larger reinforcement.
Sources:
Feng, Peng, Xinmiao Menga, Jian-Fei Chenb, and Lieping Yea. "Mechanical Properties of Structures 3D Printed with Cementitious Powders." Construction and Building Material 93 (2015): 486-97. Science Direct. Web. 28 Jan. 2016. <http://www.sciencedirect.com/science/article/pii/S095006181500690X>.
Le, T. T., S. A. Austin, S. Lim, R. A. Buswell, A. G. F Gibb, and T. Thorpe. "Mix Design and Fresh Properties for High-performance Printing Concrete." Materials and Structures 45.8 (2012): 1221-232. Springer Link. Web. 28 Jan. 2016. <http://link.springer.com/article/10.1617/s11527-012-9828-z>.
Le, T. T., S. A. Austin, S. Lim, R. A. Buswell, R. Law, A. G. F Gibb, and T. Thorpe. "Hardened Properties of High-performance Printing Concrete." Cement and Concrete Research 42.3 (March 2012): 558-66. Science Direct. Web. 28 Jan. 2016. <http://www.sciencedirect.com/science/article/pii/S0008884611003255>.
Williams, Adam. "Berkeley Researchers Pioneer New Powder-based Concrete 3D Printing Technique." Gizmag. Gizmag, 12 Mar. 2015. Web. 29 Jan. 2016. <http://www.gizmag.com/berkeley-researchers-pioneer-powder-based-concrete-3d-printing/36515/>.
Edit:
Comments on Danielle Schroder and Kai Waechter's posts.
In the past, the systems available for forming concrete are formwork (either cast-in-place or factory fabricated), "self-compacting" (which uses superplasticizers and still requires vibration), and sprayed concrete (which requires a backing material). 3D printed concrete would be able to be made without vibration or any sort of formwork or backing, which could reduce costs. However, this has not necessarily made it immediately the best option.
The major problem with this investigation is that the process still varies quite a bit, with some forms of 3D Printing using direct extrusion and others using sprayed powders. In extrusion, the most important properties for the wet concrete are the "flowability," the ability of the concrete to be pushed through the printer and form consistent filaments, and "buildability," which is required so that the mix will be rigid enough to stay in the planes and not sag while also being able to bond to the layers above.
For the sprayed powder process, the geometry may be better defined, as the layers would be much thinner. It surprised me that this type is so much less explored, but this may be because it can be considered too closely related to shotcrete. In addition, it is difficult to ensure that the water is incorporated in the powder, especially if a low water content mix is wanted.
Another complication is that 3D printed concrete is an anisotropic material because of the way it is made. Bonding between any extruded tubes and between layers has a great effect on the cured properties of the concrete. This bonding variability can increase based on the time required for formation, so larger pieces are very likely to have poor performance in shear along these planes or in tension pulling planes apart.
These points will be the major discussions to be addressed in my paper, along with the results of current testing and the future outlook for when and how 3D printing could form suitable structural concrete members. For example, I have yet to find any references to experimenting with any reinforcement other than small fiber reinforcement, and was wondering if there is any research into how a printer could perhaps print around larger reinforcement.
Sources:
Feng, Peng, Xinmiao Menga, Jian-Fei Chenb, and Lieping Yea. "Mechanical Properties of Structures 3D Printed with Cementitious Powders." Construction and Building Material 93 (2015): 486-97. Science Direct. Web. 28 Jan. 2016. <http://www.sciencedirect.com/science/article/pii/S095006181500690X>.
Le, T. T., S. A. Austin, S. Lim, R. A. Buswell, A. G. F Gibb, and T. Thorpe. "Mix Design and Fresh Properties for High-performance Printing Concrete." Materials and Structures 45.8 (2012): 1221-232. Springer Link. Web. 28 Jan. 2016. <http://link.springer.com/article/10.1617/s11527-012-9828-z>.
Le, T. T., S. A. Austin, S. Lim, R. A. Buswell, R. Law, A. G. F Gibb, and T. Thorpe. "Hardened Properties of High-performance Printing Concrete." Cement and Concrete Research 42.3 (March 2012): 558-66. Science Direct. Web. 28 Jan. 2016. <http://www.sciencedirect.com/science/article/pii/S0008884611003255>.
Williams, Adam. "Berkeley Researchers Pioneer New Powder-based Concrete 3D Printing Technique." Gizmag. Gizmag, 12 Mar. 2015. Web. 29 Jan. 2016. <http://www.gizmag.com/berkeley-researchers-pioneer-powder-based-concrete-3d-printing/36515/>.
Edit:
Comments on Danielle Schroder and Kai Waechter's posts.
Cathlene,
ReplyDeleteVery interesting topic - even though there is still a lot of research and testing to be done, this type of 3D printing could transform building design and construction. I am a bit skeptical that we will see this applied in the near future because of the two issues of buildability and flowability like you mentioned. It is a really interesting concept but there are still huge developments to be made before we see this applied at such a large scale as a building envelope. I think architectural firms will be the most eager to adopt this technology for modeling complex forms and curved facades. This type of advancement will also call for a new skill set in the structural engineering field, since designers will need advanced software to model stresses around the built-in openings for duct mains, conduit, and piping.
Cathlene,
ReplyDelete3D printed structural material is still coming along, so hopefully you'll be able to find enough research about it! I'd be interested in seeing, as you mentioned, the anisotropy of concrete formed in layers, and how significant the effect would be. I'm sure it would have to do with the type of concrete and more importantly the time between pouring layers, and there's probably research already done on this topic since it's integral to the structural performance.
I think this is a very interesting and useful topic, 3D printing technic has been use a lot of area today, and I believe the use area for it in the future will be much more wider, especially in the medical area, I saw a news last month about doctor used 3D printing technic to build a back bone and put into someone's body, I think we will see more and more this kind of case in the future.
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