> Allium adds a thin protective layer of stainless steel on top of traditional steel rebar to make it more resistant to corrosion
So it's like galvanizing but with stainless steel. Thing is, stainless steel still rusts; just how much depends on a number of factors. And if you slightly nick the stainless coating to expose the iron rebar, now the whole rebar rusts.
Maybe it will reduce the amount of corrosion, and that's great. But I highly doubt it would double the life of bridges.
h4ck_th3_pl4n3t · 2h ago
And the acidic rain is contributing to the problem. The reason infrastructure rusts so quickly in those areas is the pollution through gasoline and diesel based engines. The rain collects the gases and binds them, leading to to an acidic solution that attacks the metal and concrete.
In Europe there is a startup that tries to combat this with embedded bacteria and limestone plates that are put into the concrete. If the concrete gets a crack, the rain gets into the crack and activates the bacteria which is producing limestone to fill in the gaps. [1] [2]
That approach has a much better chance to improve infrastructure lifespan in my opinion, because just putting more steel into it is not something that's affordable. Iron as a resource is way too rare as it is already.
The claim is that it will reduce corrosion by 3x. If corrosion of rebar is the primary bottleneck to bridge longevity, a 3x longer life seems like a reasonable claim.
Of course in practice if this rebar is used in a bridge you might start to discover other things become the bottleneck, but that remains to be seen.
mmooss · 4h ago
The technological innovation is to solve the problem of why this wasn't done previously - preventing corrosion with stainless steel coating seems obvious, so what held people back? Unfortunately, the article doesn't describe the problem or how they solved it - does anyone know?
Glyptodon · 1h ago
Based on the process being roller driven and not involving drawing,I'd infer that it's probably similar to wrapping the bar with another layer at some point in the process and continuing to roll it. I'd also infer that they don't care about having the ends "capped" with stainless since everyone tends to assume that rebar can be cut off when needed. But YMMV, I'm mostly familiar with much smaller scale fabrication.
abakker · 3h ago
this is costly and difficult. The reason they didn't do this before is that it is only necessary in some construction, and because rebar has to be as cheap as possible.
cyberax · 3h ago
Stainless steel is not _completely_ stainless. It corrodes just fine if it doesn't have access to oxygen to form a protective oxide film (crevasse corrosion). But the bigger problem is that stainless steel has significantly worse mechanical characteristics, _and_ it's significantly more expensive.
Regular steel can also be protected from corrosion using paint, zinc coating, cathodic protection, etc.
Engineering is always an exercise in trade-offs. And it's almost always better to build four bridges that can stand for 100 years, instead of one bridge that can stand for 500 years.
londons_explore · 4h ago
When one rolls dissimilar metals together, they tend not to bond.
If the bond breaks in the end product, the building falls down as the carbon steel inner core slides out of the stainless coating.
How is that solved?
idiotsecant · 3h ago
Oh no! Use of dissimilar metals in a load-carrying application is bound to result in structural failure?!?! Quick, someone get started on replacing the gazillion miles of Aluminum Conductor Steel–Reinforced (ACSR) cable that run our power networks!!! While you're at it make sure to get rid of all the Titanium-clad carbon steel pressure vessels used in marine applications,Zinc-Aluminum 'Galfan' rebar, steel-aluminum galvanic isolation ship hull transitions, and any of the other bazillion places we do this!
Quick!!!
londons_explore · 4h ago
5% stainless by weight is going to add quite a decent chunk to the costs...
bagels · 4h ago
I'm sure the governments buying bridges don't care, but 5% increased cost for a multiple in longevity seems like a good investment.
adrianN · 2h ago
At least where I live the government is happy to spend a million euros every year to postpone a five million one time cost.
mjmas · 3h ago
would more probably be around 15-20% extra price because of the relative price of stainless
bell-cot · 2d ago
I might take the article seriously if it openly admitted that anti-rust coatings on rebar have been a thing for a century-ish, then talked honestly about which applications this new tech was actually better for.
One clear downside to stainless-coated rebar: During construction, rebar is very commonly welded. Welding stainless ain't just the same tools & techniques as welding conventional rebar. Plus, welding stainless gets you into chromium hazmat territory.
garbagewoman · 4h ago
Not sure why it would be any different when welding - the stainless coating isn’t the weight bearing part
bagels · 4h ago
Different welding chemistry, different welding requirements (filler, temperature, possibly process).
As the GP points out, the chromium when vaporized is a lot worse for you than what's typically in plain steel.
Not just that, but, if you weld it, now you have exposed the plain steel and have invited rust inside the coating.
garbagewoman · 2h ago
You wouldn’t be welding the stainless
dylan604 · 3h ago
if you're only welding the stainless coating, i doubt that would be as strong as if you were to weld the inner rebar directly. do you expect them to re-coat with stainless after these welds?
garbagewoman · 2h ago
That’s my point, you would not be welding the stainless part
brendoelfrendo · 2h ago
If your welding disturbs the coating and leaves gaps or cracks in the stainless coating, it will allow air and moisture to contact and corrode the carbon steel core. And once the core corrodes, the stainless coating becomes the weight bearing part, and you have a massive problem. Assembling this would presumably require some care and expertise beyond normal rebar.
garbagewoman · 2h ago
Ok sure yes that does sound bad, so any welded parts would need to be protected
entangledqubit · 5h ago
Still waiting for basalt rebar to become more of a thing. This version plays to the steel industry at least?
telotortium · 3h ago
Can someone tell me why rebar isn’t more often cathodically protected with electric current? I don’t think much power is required to resist corrosion, and it shouldn’t be too hard to test for electric continuity in the field.
ta988 · 3h ago
How do you do it at scale and without major transformations of the production lines.
Now you need to handle liquids and electricity and your process is not as continuous.
conradev · 2h ago
Can you do it with magnets?
brudgers · 13h ago
Stainless steel rebar is uncommon for the same reasons galvanized rebar and epoxy coated rebar are not common.
As materials they are massively more expensive than carbon steel and first cost matters because public infrastructure is financed with bonds and financial markets dictate bond terms of 30-40 years.
To put it another way, any belief that construction markets are inefficient is statistically a dunning-kruger to too many sigmas. Construction goes back at least as far as anything we call as civilization.
jefftk · 4h ago
This isn't stainless rebar, it's stainless-coated rebar. Perhaps still to expensive to end up widely used, but it should be a lot cheaper than pure stainless.
brudgers · 3h ago
Galvanized rebar and epoxy coated rebar have been available for many decades.
They are so much more expensive than ordinary carbon steel rebar to be unicorn poop rare.
If there is a break in the finish, it is as susceptible to corrosion as carbon steel. This means every step requires special handling and rigorous inspection. It cannot be field fabricated with a hand bender if a stirrup is missing or damaged. Tying and placement has to be done with unusual care to avoid damage (and again non-standard level of inspection).
Galvanizing and epoxy coating are long lead time and require prefabrication (bending). So you are shipping, handling and receiving bespoke space filling shapes instead of commodity straight bars to specialty job shops with limited capacity and well booked dance cards.
At every step, everyone has to price their work against all that complexity, uncertainty and potential for delays.
jpgvm · 3h ago
Galvanized rebar is about 20% more expensive and is actually widely used in highway construction, particularly when salt is a major concern.
Epoxy coated rebar turned out to have much poorer efficacy than originally expected as you noted but the same is not true of galvanizing which is a much more durable coating.
nullc · 3h ago
Galvanizing still works if there are scratches in the finish because there is a radius of protection from the galvanization.
burnt-resistor · 3h ago
Wasn't it found that epoxy-coated rebar actually doesn't help that much because it rubs off during construction?
meroes · 4h ago
What about for private construction?
brudgers · 3h ago
You can get anything you are willing to pay for.
Talk to your architect…if I were still practicing and cost was no object, I would probably recommend epoxy coated and 6kpsi concrete and a specialty contractor [1]. I would not recommend someone’s theory over technologies with track records.
[1] And require a percentage of construction cost contract.
chongli · 5h ago
There is a big inefficiency in construction markets but it's not in materials, it's in labour. Immigration laws starve construction companies of workers. With unfettered immigration it would be much easier to build simply due to a large availability of unskilled labour. The other side of the coin is of course planning, zoning approval, codes, bylaws, and other regulations that slow down construction projects and discourage development.
We've made it very hard to build because we really don't want to build. Homeowners are mostly interested in protecting their investment which means keeping housing demand high.
brudgers · 4h ago
it would be much easier to build simply due to a large availability of unskilled labour
Money makes construction easier. For example it facilitates hiring skilled labor (or pays for stainless steel rebar).
The US housing market is shaped by two facts.
1. Housing is just about the “lowest and worst” [1] way to realize returns on real-estate.
2. It is about as hard (and often harder) to build inexpensive housing as expensive housing.
> With unfettered immigration it would be much easier to build simply due to a large availability of unskilled labour.
Isn't that ultimately an economic question - increase the supply and the cost drops, increasing the number of projects where the labor cost effective but driving down wages?
If the US did have much more immigration of unskilled contruction labor, but they unionized, keeping their wages higher, would that have the same result? That is, is your argument more than, effectively, exploiting labor?
burnt-resistor · 3h ago
There are a couple of ways to prevent corrosion of bare metal even in the absence corrosion inhibitors: keep the humidity low and the Ph high.
Coatings, inhibitors, and additional barriers to water/moisture intrusion help too.
pmarreck · 3h ago
Instead of stainless steel coated rebar, someone needs to start a startup that rediscovers the Roman "self-healing cement" formula that uses lime or something
guywithahat · 3h ago
I’m pretty sure the secret to that was not inventing 4-ton vehicles. Plus there were some benefits to saltwater for construction near the ocean and some of the local soil/volcanic ash had beneficial properties, but vehicle weight was the biggest factor as far as I’m aware
0xbadcafebee · 3h ago
They already did. It's just a more expensive formulation of concrete. In general you use a mix of concrete that's as cheap as you can afford, and tuned to the specific engineering requirements of that concrete structure. (We mostly use concrete because it's cheaper than alternatives)
So it's like galvanizing but with stainless steel. Thing is, stainless steel still rusts; just how much depends on a number of factors. And if you slightly nick the stainless coating to expose the iron rebar, now the whole rebar rusts.
Maybe it will reduce the amount of corrosion, and that's great. But I highly doubt it would double the life of bridges.
In Europe there is a startup that tries to combat this with embedded bacteria and limestone plates that are put into the concrete. If the concrete gets a crack, the rain gets into the crack and activates the bacteria which is producing limestone to fill in the gaps. [1] [2]
That approach has a much better chance to improve infrastructure lifespan in my opinion, because just putting more steel into it is not something that's affordable. Iron as a resource is way too rare as it is already.
[1] https://www.epo.org/en/news-events/european-inventor-award/m...
[2] https://en.m.wikipedia.org/wiki/Bacillus_pseudofirmus
Of course in practice if this rebar is used in a bridge you might start to discover other things become the bottleneck, but that remains to be seen.
Regular steel can also be protected from corrosion using paint, zinc coating, cathodic protection, etc.
Engineering is always an exercise in trade-offs. And it's almost always better to build four bridges that can stand for 100 years, instead of one bridge that can stand for 500 years.
If the bond breaks in the end product, the building falls down as the carbon steel inner core slides out of the stainless coating.
How is that solved?
Quick!!!
One clear downside to stainless-coated rebar: During construction, rebar is very commonly welded. Welding stainless ain't just the same tools & techniques as welding conventional rebar. Plus, welding stainless gets you into chromium hazmat territory.
As the GP points out, the chromium when vaporized is a lot worse for you than what's typically in plain steel.
Not just that, but, if you weld it, now you have exposed the plain steel and have invited rust inside the coating.
Now you need to handle liquids and electricity and your process is not as continuous.
As materials they are massively more expensive than carbon steel and first cost matters because public infrastructure is financed with bonds and financial markets dictate bond terms of 30-40 years.
To put it another way, any belief that construction markets are inefficient is statistically a dunning-kruger to too many sigmas. Construction goes back at least as far as anything we call as civilization.
They are so much more expensive than ordinary carbon steel rebar to be unicorn poop rare.
If there is a break in the finish, it is as susceptible to corrosion as carbon steel. This means every step requires special handling and rigorous inspection. It cannot be field fabricated with a hand bender if a stirrup is missing or damaged. Tying and placement has to be done with unusual care to avoid damage (and again non-standard level of inspection).
Galvanizing and epoxy coating are long lead time and require prefabrication (bending). So you are shipping, handling and receiving bespoke space filling shapes instead of commodity straight bars to specialty job shops with limited capacity and well booked dance cards.
At every step, everyone has to price their work against all that complexity, uncertainty and potential for delays.
Epoxy coated rebar turned out to have much poorer efficacy than originally expected as you noted but the same is not true of galvanizing which is a much more durable coating.
Talk to your architect…if I were still practicing and cost was no object, I would probably recommend epoxy coated and 6kpsi concrete and a specialty contractor [1]. I would not recommend someone’s theory over technologies with track records.
[1] And require a percentage of construction cost contract.
We've made it very hard to build because we really don't want to build. Homeowners are mostly interested in protecting their investment which means keeping housing demand high.
Money makes construction easier. For example it facilitates hiring skilled labor (or pays for stainless steel rebar).
The US housing market is shaped by two facts.
1. Housing is just about the “lowest and worst” [1] way to realize returns on real-estate.
2. It is about as hard (and often harder) to build inexpensive housing as expensive housing.
[1] https://en.m.wikipedia.org/wiki/Highest_and_best_use
Or use well paid skilled labor and machines?
Isn't that ultimately an economic question - increase the supply and the cost drops, increasing the number of projects where the labor cost effective but driving down wages?
If the US did have much more immigration of unskilled contruction labor, but they unionized, keeping their wages higher, would that have the same result? That is, is your argument more than, effectively, exploiting labor?
Coatings, inhibitors, and additional barriers to water/moisture intrusion help too.