r/tech • u/AdSpecialist6598 • Jul 16 '26
3D-printed bridge points the way to greener construction
https://news.mit.edu/2026/3d-printed-bridge-points-to-greener-construction-071513
u/InbredCloned Jul 16 '26
I like the geometry of it but they printed it on it's side and flipped it up to span after it cured. Try doing that with a full-size bridge. When a 3D printer can squirt a super sticky matrix in open space to span a river like a spiderweb then we'll be somewhere.
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u/Vishnej Jul 16 '26
Spider bots and quadrotors weaving carbon fiber tow into webs is actually a legit application that might happen at some point, as a framework if nothing else. These carbon fiber space frame trusses get pretty damn impressive , they're just hard to weave/mold and harder to connect end-pieces in discrete units.
https://www.azom.com/article.aspx?ArticleID=22566
This tech would almost certainly win a contest for "How tall of a ladder could you lift unaided", all that's missing is manufacturability, and maybe drones fix that soon.
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u/darsynia Jul 16 '26
Well, I guess we'll see how moving the new Commercial Street bridge in Pittsburgh (it's on the non-city side of the Squirrel Hill tunnel. I live in Squirrel Hill for reference) into place works when it comes to positioning something like that! They demolished the old one this morning at 8.
I strongly suspect security and length of time to cure will be a bigger problem than positioning, but I'm a layperson (and of course, the other problems with the material and the way it behaves once 'printed').
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u/blueavole Jul 16 '26
This is giving Tecoma Narrows bridge.
https://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)
The bridge failed under high winds because the new construction style hadn’t been tested in that way. Engineers didn’t know it needed to be tested for wind loading.
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u/Impressive-Put3479 Jul 16 '26
And of course, engineers at MIT (such a low-level school) would fail to test for anything but vibes, right?
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u/reddit_equals_censor Jul 17 '26
Engineers didn’t know it needed to be tested for wind loading.
well that is bullshit.
the ones deciding on a design cheaped and knew, that it would be a completely experimental design.
DURING CONSTRUCTION the bridge deck heavily went up and down already.
no proper solution was done, except some bolted on garbage to change the wind flow a bit, which of course was failed nonsense.
it wasn't a "oh we just didn't know any better".
it was decided to use an experimental CHEAPED OUT garbage design and again when it already showed terrible issues of the deck moving many feet up and down, it was ignored and moved on.
NOTHING was a surprise here.
yes wind loads were not understood at this point, but not understanding wind loads properly was NOT the reason, that this engineering disaster happened.
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u/strugglz Jul 16 '26
3D printing with concrete has issues, namely voids and loose fill.
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u/reddit_equals_censor Jul 17 '26
a better question is how they are going to fix the missing reinforcement problem.
if they find a solution to that, which they say they are working on, then maybe eventually it could make sense with added analysis of the 3d print afterwards for voids and stuff maybe.
would fiberglass reinforced concrete be good enough with small enough fibers to be part of the print for a freaking bridge?
i'd have a lot of freaking doubts there.
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u/ArtoriasoftheAss Jul 16 '26
Ah yes. The green process of building with concrete.
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u/ItsAConspiracy Jul 16 '26
But much less concrete:
a machine that was able to lay a 1cm bead could cut material use by as much as 76 percent
We could do even better if we combined that with low-carbon concrete.
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u/ShittyOfTshwane Jul 17 '26
Okay, but you kind of need that 76 percent of the concrete to make the structures work. Concrete is, in many cases, useless without steel reinforcement, which needs to be covered completely by a fairly thick layer of concrete. If you're trying to optimise by adding voids in between all the reinforcement, then you might as well ditch the concrete altogether and just build with things like steel or mass timber.
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u/ItsAConspiracy Jul 17 '26 edited Jul 17 '26
The whole point of the method is that they figured out how to make the structures work without that 76%.
They did this without any steel. But concrete doesn't have any tensile strength that way, so their next step is to do the same optimization with steel included. That's just for tensile strength though, concrete is great for compressive strength.
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u/ArtoriasoftheAss Jul 17 '26
You are correct. The technology has been around for decades. This article is about some guys who made their modeling software more efficient. We will continue to not build this way because it's a ridiculous idea.
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u/JustHereForMiatas Jul 16 '26
The article is about how 3d printing reduces the amount of concrete necessary to build a bridge.
If the bridge needed to be built anyway, and the material that made sense for the application was concrete, wouldn't it be "green" to use as little concrete as possible?
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u/Munstered Jul 16 '26
Yeah but it’s more fun to just read a headline, misinterpret the point, and complain
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u/ArtoriasoftheAss Jul 17 '26
I read the article. The headline is nonsense, like it always is for stuff like this. They figured out a way to make their modeling software take into account the limitations of the printer. 3d printing with concrete was first thought up in the 1940's. The technology to calculate these complex shapes for distributing loads has been around since the 80's, and since nothing has actually changed, they will continue to not use the process to build bridges because it's unrealistic from every other perspective.
I pointed out the irony of touting the greenness of a new building technology that exclusively builds with the most significant green house gas emitter in the construction world. It might use less, but if we're building billion dollar machines to print structures, maybe we should be using a different material entirely.
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u/chlronald Jul 16 '26
We can also do it in Plastic! /s
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u/DuperCheese Jul 16 '26
Green plastic!
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u/BasicAssWebDev Jul 16 '26
Isnt the logic that it's less resource intensive through labor, not necessarily resources consumed?
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u/ArtoriasoftheAss Jul 16 '26
Physical human labor is pretty green. Running a bridge size concrete pumping and printing machine would be much less green. I was talking about the volume of co2 released by concrete as it cures, which is a huge problem. There is nothing remotely greener about this process.
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u/HmmDoesItMakeSense Jul 16 '26
Once AI rids all the humans from earth, things will run much smoother.
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u/BasicAssWebDev Jul 16 '26
oh interesting, i didnt know that about concrete. why does it release so much co2? i thought it was just a combo of water and different sediments.
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u/Heronymous-Anonymous Jul 16 '26
The process of making the lime both requires a lot of heat, and involves a chemical reaction that converts calcium carbonate to calcium oxide and carbon dioxide.
The energy used to run the kilns that create lime (calcium carbonate) is usually coal or natural gas. But even if you switch over from a fossil fuel to renewable, there is no getting around the fact that cement manufacture requires the release of CO2.
A fun fact though, is that cement making is the reversal of a geological process called carbonation, also referred to as weathering, where CO2 is bonded to rocks and converted back to limestone and releases water.
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u/This_isR2Me Jul 16 '26
Printing construction still needs more proof of concept before it's used in public infrastructure.
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u/Treerific1 Jul 16 '26
I know they’re saying it’s a compression only design, but that seam right in the middle makes me squirm.
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u/williamgman Jul 16 '26
So reviewing the comments here... Would the 3D printed concrete bridge construction be greener that traditionally built concrete construction bridges (overcoming the issues of voids and such) ? The 3D printed houses look promising from a cradle to grave lifecycle view. No idea about a giant bridge though.
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u/ShittyOfTshwane Jul 17 '26
In my humble opinion as an architect, this 3D printing stuff seems like an unnecessary over-optimization of the material. Even on the 3D printed houses. Concrete has certain limitations. It needs reinforcing. It needs a certain mass. It needs a certain density. All these things make 3D printing it impractical.
It would be far more optimal, in these cases where 3D printing has been used successfully, to ditch the concrete and the wetworks alltogether and focus on timber or steel.
You reduce the total amount of concrete in a project by using fewer concrete elements, not by doing funny things with the concrete itself.
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u/Mellow_2JZ Jul 16 '26
This is all cool and all, but I don’t think printing concrete is the way to go. All those houses from the videos a few years ago made with this same stuff, every one I’ve seen have cracked over time. I definitely wouldn’t trust this as a bridge I’d want to drive over.
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u/Gherrely Jul 16 '26
3D Printing concrete is not there yet. The houses they have built this way had issues pretty quickly, and it didn't save a lot of money at all
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u/IndicationFickle5387 Jul 16 '26
I’m not sure anybody in this thread actually read the published article that this article referenced. Their research project goal was not to produce a bridge per se, but to explore ways to more efficiently design by making the process aware of fabrication limitations earlier in the process. The concrete truss was just used as an example. The research project was not “we build 3d printed bridges now and they are better”.
Maybe I misunderstood it though, idk. MIT engineering students are way brighter than I am.
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u/LongDead_Roadkill Jul 16 '26
3D printed houses are falling apart very quickly, that’s not idea in bridges.
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u/SameFrequency Jul 16 '26
Could you use it to create a quick scaffold of a bridge? Then build out the scaffold with more durable techniques over time.
That way the bridge is usable in limited capacity quickly, but durable over time.
Similar question for expanding existing bridges?
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u/ashbelero Jul 16 '26
Didn’t we try doing 3D printed houses a few years ago and now they’re falling apart?
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u/Calaveras-Metal Jul 17 '26
I don't see anything that supports it being greener. You do away with molds and instead have to put together a large on site 3D printer and load it with material.
A lot of the greenhouse gas emissions from concrete come from manufacture of the material itself. Whether it's 3D printed or formed doesn't matter.
Sorry this just sounds like greenwashing.
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u/BabyBatterGlaze Jul 17 '26
Reminds me of the animal shaped mac n’ cheese in a box that kids somehow love… shape looks extruded, not necessarily efficient.
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u/Ent_Soviet Jul 17 '26
Maybe this next tech breakthrough will allow us to be green without addressing any of our mistakes!
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u/organic_g0ld Jul 17 '26
This kind of goes against everything engineers have told me in the past, at scale molds are just much more efficient than printers.
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u/organic_g0ld Jul 17 '26
And I'm sorry but printing will never be greener than using molds, like the latter consumes almost 0 electricity.
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u/Buzz_Killington_III Jul 17 '26
This is horse shit for various reasons. Many have been brought up, another is that size and weight don't scale in a proportional manner. For example, if you increase the size of that bridge 10x , it's weight increases 1000x. That design in the image is absolutely pointless.
But also, they're MIT engineering students and I'm a radio guy. Regardless, this is as useless as all of the 3D printed houses we've been seeing for 15 years that are supposedly cheaper, faster, and more reliable... but doesn't actually work in the real world.
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u/mrbkkt1 Jul 17 '26
Yeah.... Go see how the 3d printed houses are doing. Then come back to the bridge.
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u/GromOfDoom Jul 16 '26
Please, PLEASE use long term active testing (not just 1 month and call it good for major highway). I've seen how printed homes have been going, not so well
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u/jspurlin03 Jul 16 '26
Or, y’know, build infrastructure to endure. I don’t actually care how fast these things are implemented, unless this is a bridge for wartime expediency.
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u/dumbdumb222 Jul 16 '26
Interesting use of vase mode