Today the Built Environment department's concrete printer starts printing the world's first 3-D printed reinforced, pre-stressed concrete bridge. The cycle bridge will be part of a new section of ring road around Gemert [Netherlands] in which the BAM Infra construction company is using innovative techniques.
[O]ne of the advantages of printing a bridge is that much less concrete is needed than in the conventional technique in which a mold is filled. By contrast, a printer deposits only the concrete where it is needed. This has benefits since in the production of cement a lot of CO2 is released and much less of this is needed for printed concrete. Another benefit lies in freedom of form: the printer can make any desired shape, and no wooden molding frames are needed.
They have managed to not only 3-D print concrete, they have also developed a technique to lay down a cable within the concrete so that it can be 'pre-stressed' — avoiding tensil stress.
The researchers successfully tested a 1:2 scale model under a 2000kg load.
(Score: 2) by Immerman on Saturday June 24 2017, @02:58PM
The only "First" I see is
> the world's first 3-D printed reinforced, pre-stressed concrete bridge
Wherein the "3-D printed" part is clearly mentioned first. You've got to have some pretty dodgy comprehension skills to convert that to a claim of the first pre-stressed concrete structure of any type. May as well interpret "Genetic engineers create world's first glowing rabbit" is a claim to have created the first rabbit.
Excellent in-depth information though, thank you. Even though it is very disappointing. I mean post-stressed concrete is definitely a step in the right direction, but it's not exactly new technology, and using it with printed concrete components verges on the blindingly obvious.
If they had prestressed the concrete, I would certainly not expect the cable to be fed from the print head, for exactly the reasons you mention. Instead, I would expect a second system to place and hold the cables so that they maintain tension along useful directions - potentially parallel to the printing, but not necessarily.
As for filling cast concrete with styrofoam or other filler, that's certainly old news (and foamed concrete is extremely interesting, there's even some promising cheap and low-tech DIY options out there that I'd love to try if I ever have the excuse) . What 3D printing offers though is well-ordered structure within the mostly-hollowed space in order to maximize the strength supplied by a given amount of concrete honeycomb, based on the specific loading requirements of the application. You could theoretically get comparable results by prebuilding a styrofoam-and-rod structure within your forms to create the desired hollows, in fact that might be much superior since you can avoid the inter-layer bonding issues, but that's going to be *extremely* labor-intensive in comparison.