> 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.
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.
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 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?
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.
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.
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.
> But the bigger problem is that stainless steel has significantly worse mechanical characteristics
This is a common claim, but I’m not sure I really believe it. Even for applications that require especially good mechanical characteristics, e.g. tool steels, good stainless alloys can be very good.
I would believe that the stainless alloys that are widely available in large quantities at somewhat reasonable prices for structural use (e.g. 304 and 316 stainless steel) have mediocre mechanical properties.
They somehow made stainless steel _coating_. So theoretically you should be able to get the mechanical benefits of high-carbon steel, and corrosion resistance of stainless steel.
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!
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.
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?
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.
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.
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.
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.
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.
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.
If you’re building a house: waterproof the structure correctly. This will protect most of your rebar, and it will protect your walls, your finishes, and keep mold from growing.
The lifespan of ordinary rebar in competently cast concrete that is kept dry is very, very long. Maybe if you live right next to the ocean you will have somewhat different considerations, but a quality waterproofing membrane on the outside of your foundation is worthwhile anyway and will help control salt spray as a side benefit.
If you visit, say, an 20 year old, incompetently built structure in a place with real weather (ski lodges are often like this), you can see that the concrete will be in perfectly fine condition, but the structure may smell moldy and interior finishes will be failing.
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.
Construction sites need unskilled labour to haul things around, clean up the jobsite, hold heavy objects in place until they’re fastened, and the like. There aren’t any construction site robots that I know of which can replace all the jobs an untrained but otherwise strong and healthy human can do.
A strong trained human can do all the things you mention with less supervision and in less time.
In other words if there is a lot of work for untrained workers, it is a poorly run construction site. In a well run construction project, trained workers clean up after themselves and installers don’t need additional people holding up heavy objects during placement because they bring proper tools, staff, and falsework with them.
> 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?
Unionization only works if the union has the power to exclude replacement labour from the jobsite. “Exploiting” labour is a meaningless value judgement. There’s no scientific definition of what is exploitation and what isn’t.
Back in the late 19th / early 20th century we had no restrictions on immigration, minimal state welfare programs, and no minimum wage laws. Huge numbers of people migrated to the US for work, they rapidly built infrastructure and buildings in cities like New York and Chicago. There was high upward social mobility.
All the problems started with minimum wage laws and the welfare state. You can’t have a functioning welfare state with unrestricted immigration. When you restrict immigration you essentially create a black market for below-minimum wage labour. That’s why the US has such a huge number of illegal immigrants: to do the jobs that nobody else wants in construction and agriculture.
Before all this (effectively) regulation and restriction of the labour market, you had the ability for people to learn skilled trades on the job. That was a form of non-monetary compensation that is no longer economically viable due to minimum wage laws. Minimum wage laws set a floor on the amount of productivity a worker must supply before you can hire him.
The other problem we’ve caused with these laws is inflation. The cost of living has skyrocketed. People on minimum wage today are in many ways economically worse off than the migrant workers arriving in droves before minimum wage laws existed!
> “Exploiting” labour is a meaningless value judgement. There’s no scientific definition of what is exploitation and what isn’t.
Values are our goals, the most important things we have. The world certainly isn't limited to things with a scientific definition. (Also, I expect there are plenty of legal and related definitions of labor exploitation.)
> There was high upward social mobility.
You'll need to document some of these claims. Unions started because working conditions and pay were awful; people were widely exploited - including injured, cheated, etc. - due to their fundamentally weak marketplace position: the owner controls all the jobs, the worker only controls one.
Since unionization, the economy, pay, and working conditions have all boomed. It's hard to argue with the results - the greatest economic performance in history.
Yes, the wealthy and powerful don't get as much of the pie, but the pie is much larger.
> The other problem we’ve caused with these laws is inflation. The cost of living has skyrocketed. People on minimum wage today are in many ways economically worse off than the migrant workers arriving in droves before minimum wage laws existed!
That is a complete falsehood.
> unrestricted immigration
When and where has that happened? Who supports that? It's quite a strawperson.
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.
Rebar is often part of a structure’s electrical ground. Any protective current supplied might end up exiting through other connected grounds and doing little good.
How do you do this on a bridge? The rebar is one electrode. Where’s the other?
Even if you get it working, I would be a bit nervous about the reaction products. If there’s any current flow, then something is being reduced. If the medium is moist concrete, then it might well be water that gets reduced to hydrogen gas and hydroxide ions. The hydroxide ions may be harmless, but the hydrogen could be problematic.
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
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
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)
> 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.
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.
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.
[1] https://www.epo.org/en/news-events/european-inventor-award/m...
[2] https://en.m.wikipedia.org/wiki/Bacillus_pseudofirmus
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?
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.
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.
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.
> But the bigger problem is that stainless steel has significantly worse mechanical characteristics
This is a common claim, but I’m not sure I really believe it. Even for applications that require especially good mechanical characteristics, e.g. tool steels, good stainless alloys can be very good.
I would believe that the stainless alloys that are widely available in large quantities at somewhat reasonable prices for structural use (e.g. 304 and 316 stainless steel) have mediocre mechanical properties.
???
Tool steels are not stainless, as anyone who forgot to stow away tools properly can confirm.
So what changed that allowed this innovation and made it attractive, at least to some extent?
They somehow made stainless steel _coating_. So theoretically you should be able to get the mechanical benefits of high-carbon steel, and corrosion resistance of stainless steel.
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?
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!!!
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.
Not sure why it would be any different when welding - the stainless coating isn’t the weight bearing part
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.
You wouldn’t be welding the stainless
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?
That’s my point, you would not be welding the stainless part
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.
Ok sure yes that does sound bad, so any welded parts would need to be protected
5% stainless by weight is going to add quite a decent chunk to the costs...
I'm sure the governments buying bridges don't care, but 5% increased cost for a multiple in longevity seems like a good investment.
At least where I live the government is happy to spend a million euros every year to postpone a five million one time cost.
would more probably be around 15-20% extra price because of the relative price of stainless
Still waiting for basalt rebar to become more of a thing. This version plays to the steel industry at least?
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.
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.
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.
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.
Galvanizing still works if there are scratches in the finish because there is a radius of protection from the galvanization.
Wasn't it found that epoxy-coated rebar actually doesn't help that much because it rubs off during construction?
What about for private construction?
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.
If you’re building a house: waterproof the structure correctly. This will protect most of your rebar, and it will protect your walls, your finishes, and keep mold from growing.
The lifespan of ordinary rebar in competently cast concrete that is kept dry is very, very long. Maybe if you live right next to the ocean you will have somewhat different considerations, but a quality waterproofing membrane on the outside of your foundation is worthwhile anyway and will help control salt spray as a side benefit.
If you visit, say, an 20 year old, incompetently built structure in a place with real weather (ski lodges are often like this), you can see that the concrete will be in perfectly fine condition, but the structure may smell moldy and interior finishes will be failing.
If you live near the ocean, usually chloride ion gets on the rebar during construction.
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.
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.
[1] https://en.m.wikipedia.org/wiki/Highest_and_best_use
“With unfettered immigration...”
Or use well paid skilled labor and machines?
Construction sites need unskilled labour to haul things around, clean up the jobsite, hold heavy objects in place until they’re fastened, and the like. There aren’t any construction site robots that I know of which can replace all the jobs an untrained but otherwise strong and healthy human can do.
A strong trained human can do all the things you mention with less supervision and in less time.
In other words if there is a lot of work for untrained workers, it is a poorly run construction site. In a well run construction project, trained workers clean up after themselves and installers don’t need additional people holding up heavy objects during placement because they bring proper tools, staff, and falsework with them.
> 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?
Unionization only works if the union has the power to exclude replacement labour from the jobsite. “Exploiting” labour is a meaningless value judgement. There’s no scientific definition of what is exploitation and what isn’t.
Back in the late 19th / early 20th century we had no restrictions on immigration, minimal state welfare programs, and no minimum wage laws. Huge numbers of people migrated to the US for work, they rapidly built infrastructure and buildings in cities like New York and Chicago. There was high upward social mobility.
All the problems started with minimum wage laws and the welfare state. You can’t have a functioning welfare state with unrestricted immigration. When you restrict immigration you essentially create a black market for below-minimum wage labour. That’s why the US has such a huge number of illegal immigrants: to do the jobs that nobody else wants in construction and agriculture.
Before all this (effectively) regulation and restriction of the labour market, you had the ability for people to learn skilled trades on the job. That was a form of non-monetary compensation that is no longer economically viable due to minimum wage laws. Minimum wage laws set a floor on the amount of productivity a worker must supply before you can hire him.
The other problem we’ve caused with these laws is inflation. The cost of living has skyrocketed. People on minimum wage today are in many ways economically worse off than the migrant workers arriving in droves before minimum wage laws existed!
> “Exploiting” labour is a meaningless value judgement. There’s no scientific definition of what is exploitation and what isn’t.
Values are our goals, the most important things we have. The world certainly isn't limited to things with a scientific definition. (Also, I expect there are plenty of legal and related definitions of labor exploitation.)
> There was high upward social mobility.
You'll need to document some of these claims. Unions started because working conditions and pay were awful; people were widely exploited - including injured, cheated, etc. - due to their fundamentally weak marketplace position: the owner controls all the jobs, the worker only controls one.
Since unionization, the economy, pay, and working conditions have all boomed. It's hard to argue with the results - the greatest economic performance in history.
Yes, the wealthy and powerful don't get as much of the pie, but the pie is much larger.
> The other problem we’ve caused with these laws is inflation. The cost of living has skyrocketed. People on minimum wage today are in many ways economically worse off than the migrant workers arriving in droves before minimum wage laws existed!
That is a complete falsehood.
> unrestricted immigration
When and where has that happened? Who supports that? It's quite a strawperson.
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.
I can guess a few reasons:
Cost. This may not be cheap.
Rebar is often part of a structure’s electrical ground. Any protective current supplied might end up exiting through other connected grounds and doing little good.
How do you do this on a bridge? The rebar is one electrode. Where’s the other?
Even if you get it working, I would be a bit nervous about the reaction products. If there’s any current flow, then something is being reduced. If the medium is moist concrete, then it might well be water that gets reduced to hydrogen gas and hydroxide ions. The hydroxide ions may be harmless, but the hydrogen could be problematic.
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.
Can you do it with magnets?
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.
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
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
I doubt that the magical Roman concrete has any appreciable tensile strength. Sometimes reinforcement is not optional.
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)
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