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posted by martyb on Friday June 23 2017, @11:53AM   Printer-friendly
from the concrete-plans dept.

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.


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  • (Score: 2) by butthurt on Friday June 23 2017, @05:48PM (3 children)

    by butthurt (6141) on Friday June 23 2017, @05:48PM (#530113) Journal

    > No one is claiming otherwise.

    The summary could be read that way.

    Basically they've figured out a way to incorporate one of the major concrete-strengthening technologies with the convenience and flexibility of 3D printing.

    They haven't. The phys.org page says:

    When laying a strip of concrete the concrete printer adds a steel cable so that the bridge is 'pre-stressed' so that no tensile stress can occur in the concrete, because this is something that concrete is not able to cope with adequately.

    I found the original press release (no thanks to phys.org) at

    https://www.tue.nl/en/university/news-and-press/news/16-06-2017-the-worlds-first-3d-printed-reinforced-concrete-bridge-starts-to-take-shape/ [www.tue.nl]

    and it says exactly the same thing; phys.org simply reprinted the press release verbatim (including the "ne" typo).

    However, I also found another report, which has a cut-away illustration of the bridge:

    http://www.3ders.org/articles/20170619-dutch-cyclists-to-enjoy-benefits-of-3d-printed-concrete-bridge-following-tu-eindhoven-bam-collaboration.html [3ders.org]

    You can see in that illustration that the steel cables are not incorporated within the printed form; rather, the printed part is sandwiched between two abutments (which don't appear to have been printed) to which the cables are attached. The accompanying video is narrated in Dutch, which I don't speak, but it shows workers manually adding the cabling.

    http://www.youtube.com/watch?v=NrDjDcETbls [youtube.com]

    It appears to me that the printer creates an unreinforced piece. The reinforcement is added externally by human workers. If you look at the photo on the phys.org page you can see that the printed form has a curlicue/arabesque shape. If a cable were dispensed from the print head as the shape were being printed, it would not be possible to stretch the cable before the concrete hardened, because the cable would straighten out from the tension.

    A bridge in Shanghai was built with Styrofoam blocks inside it, to reduce the amount of concrete needed.

    https://www.weirdasianews.com/2010/02/05/shanghai-wonderbridge-trash-collapses/ [weirdasianews.com]

    There also exists foamed concrete, which can include "up to 80% air" according to one purveyor.

    http://www.cemex.co.uk/porofoam-lightweight-foamed-concrete-for-voidfill.aspx [cemex.co.uk]

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  • (Score: 2) by Osamabobama on Friday June 23 2017, @07:17PM

    by Osamabobama (5842) on Friday June 23 2017, @07:17PM (#530191)

    Furthermore, this implementation is actually called post-tensioned concrete, as the tension is added after assembling the bridge.

    Wikipedia article [wikipedia.org]

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  • (Score: 3, Interesting) by Dr Spin on Saturday June 24 2017, @09:05AM

    by Dr Spin (5239) on Saturday June 24 2017, @09:05AM (#530512)

    A bridge in Shanghai was built with Styrofoam blocks inside it, to reduce the amount of concrete needed.

    Many buildings in the ancient Roman world (ie from centuries before the time of Christ) used concrete with tiny clay
    vessels embedded to keep the weight down in large dome structures. This is not a new technique, and people who
    study construction engineering at reputable universities (or Google), should be fully aware of this technique, as well
    as the one of embedding cables or wires and tensioning after the concrete sets, which I saw being done in the 1950's.

    It remains the case that 3D printing in concrete gives you abilities never seen before, but these are mostly because
    of the combination of speed and complexity of shape. In some cases, clearly, also because "trendiness" means more
    effort goes in at the design stage. You can pour a lot of concrete for the cost of a highly skilled design engineer.

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  • (Score: 2) by Immerman on Saturday June 24 2017, @02:58PM

    by Immerman (3985) on Saturday June 24 2017, @02:58PM (#530570)

    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.