There's nothing wrong with reinforced concrete, but the incentives to produce long lasting buildings are not there. The cheapest bidder will generally win and their building will last the "design life" of the building, but often not much more. The simplest way to change this is to extend the design life, which would result in stainless steels or another more expensive material being used in this application.
Reinforced concrete is much like clothing: a stitch in time saves nine. With regular cleaning and maintenance, it can last much longer than if you just let it deteriorate.
In particular one about epoxy coated rebar that gives interesting notes about why it has its problems: https://youtu.be/xVDy84rR5Z8
I had a great couple of days learning all about the complexities of concrete through his videos.
There are also interesting new methods to monitor corrosion
It is, however, more expensive ...
HD Galvanized is a coating whereas stainless steel is a different material - it is stainless all the way through ...
https://www.ijser.org/researchpaper/Epoxy-Coated-Versus-Galv... has a lot more, but clearly not a panacea...
With that in mind, it makes perfect sense to make an office building out of reinforced concrete.
[0]https://twitter.com/Paul_Denney/status/1397132479144812544
[1]https://www.punchline-gloucester.com/articles/aanews/glouces...
That's a problem in and of itself, IMO. Construction is tremendously resource-intensive. We should not be building "throwaway" buildings.
As an economics exercise, it may also be interesting to price in the cost of dismantling/disposing of construction materials into the initial construction cost. I wonder if doing so will steer materials development away from composites that are difficult to recycle towards something new.
Graphene has its own set of problems. Namely, it can be toxic to humans. [1] And who knows what massive quantities of graphene in concrete will do to an environment 10-20 years after the building's construction. Even demolition with explosives will probably be problematic due to potentially massive clouds of nanoparticles it could create.
Sure, compared to other materials it might not be as: long-lasting, cheap, sustainable, but as in all things it seems one can only pick two.
Even stainless steel rusts, just more slowly. Roughly 10-100x more slowly, judging by https://www.nrc.gov/docs/ML1124/ML112490377.pdf and https://www.mdpi.com/2076-3417/10/23/8705/pdf.
I grew up partly in an 18 story reinforced concrete building built in the 1920s. The apartment I lived in was recently sold for several million dollars.
Once, when there was a leak and the plaster came off, the underlying concrete was exposed and it scraped away like very weak sandstone.
How strong is the building and when will it collapse? Does anyone know? Is anyone testing?
I think the answer to both of those questions is "no". Everyone seems to assume they will stand forever. They won't.
I think buildings that are too regularly under construction should carry some tax penalties, instead renovating non-durable buildings to tastelessness is a way to save on property taxes, get tax deductions and try to pressure tenants out to get the latest upscale rates.
Or if it's made of stone. Stacking giant stones on top of each other is a sure-fire way to make a building outlive you.
After that, the longest-lived buildings that I am aware of are made of wood. The catch is they've been rebuilt 50 times, once per time they burned to the ground.
After those, the longest-lived buildings are made of Roman concrete that we can't reproduce. (To give you an idea how insane Roman concrete was, you can go kayaking north of Naples, and kayak through a concrete Roman building that is sitting on piles in the Mediterranean sea)
B - Construction is resource intensive, no doubt about it. Without this technique the costs and resources would go up, double?, more? Many structures we take for granted, like freeway overpasses, would be impossibly expensive.
Sometimes, building to throw away is the best model. If something is so resource intensive in a way where the externalities are not appropriately mitigated, the right way is to tax the externalities, not to go after specific things.
If these builds were too expensive to build, they wouldn't be built.
Concrete however does an excellent job of externalizing its costs: into the atmosphere, forward through time, and onto other people. So it will remain popular so long as those remain the expressed values of society.
Edit: Awww, boo hoo!
New footings, beams, walls, etc are constructed or installed to replace old ones all the time.
Say you have a bad concrete footing for a post. You use jacks to support the beam on both sides of the post that sits on the footing, remove the post, remove the footing, pour a new footing, and then put a new post in and remove the beam jacks.
Saying we shouldn't have buildings that only last 50 years but rather they should last 500 is like saying they shouldn't last 50 years but instead 5. Maybe. Maybe 5 makes sense.
My assumption would be - shocker - it's probably a complicated trade off that's best adjudicated by the people with the most skin in the particular game.
Simple, for externalities, you directly charge for the externality.
All these stop-gap "it costs carbon, so we must make it last 50 years" is like placing massive `if-then-else` statements throughout your codebase and then being surprised when the emergent behaviour of your program somehow results in uglier, more carbon polluting, sicker buildings that are now 100 years old and imposing massive costs on society around them.
My understanding that the economics have already really pushed us massively forwards in the past decade or two, that we are far more aggressive about recycling construction aggregate[1].
The article has a nod midway through to these concerns,
> The many alternative materials for concrete reinforcement – such as stainless steel, aluminium bronze and fibre-polymer composites – are not yet widely used. The affordability of plain steel reinforcement is attractive to developers. But many planners and developers fail to consider the extended costs of maintenance, repair or replacement.
This definitely seems like a huge societal blind-side to me. As much as it's an issue of planners and developers, I feel like there's a consumer lack of understanding. The invisible hand can't push effectively here, can't reward the builders doing it right adequately. In part because society is not aware, doesn't know what to ask for, doesn't have standards, doesn't view & comprehend the role of maintenance & ultimately recycling. These are far off things.
As my generation starts to see the limits of sustainability, see where so very many many creations begin to become risks & hazards & losses rather than values, we may develop some sense, but switching over into a fear-based emotional reaction isn't necessarily a great fix. Trying to give us all a picture of the life-cycle, the costs, the trade-offs; that seems like the necessary task. Regulating our ability to see & ascertain.
Hopefully we just get better & better about recycling. It'd be so interesting to see how reinforcements are extracted from construction aggregate today. Stainless steel reinforcement isn't expensive... if you can safely view it not as a sunk construction cost, but as a semi-long term loan for a building. Where-as more advanced materials like fiber-polymer, I tend to imagine, may have wonderful characteristics in use, I also tend to imagine them as likely having less recoverability. Steel: material we know how to re-cast.
None of the owners want to know that their investments are worthless. So nothing will be checked unless its required by law.
Just FYI, on a ‘plan and spec’ construction project, all material is specified by the architect and engineers. If the project specs say you have to use stainless steel rebar, then even the low bidder will have it included.
What hubris for a landowner to assume there will be a need for a building 1000 years hence.
Buildings aren’t usually demolished and replaced because they are dilapidated; rather, it’s because the new owner has a different need (and a different aesthetic.)
A building that takes 1000 to crumble is just as a much a blight — maybe more — as a plastic bottle that takes 10,000 years to crumble.
If population levels change, up or down, we are going to have to be continually adjusting our usage of space to account for this. Making it easier to modify and/or tear-down-and-rebuild would make things a lot more efficient there. You'd need some policy changes too to fix the problems of, say, homeless people sleeping outside empty office buildings, but getting construction costs down would be a huge part of this.
We shouldn't be so arrogant to assume we are planning the right construction to serve us well for hundreds of years.
The materials are important, but they can be misused, and master craftsmen can use them far better than I ever will, So the methods matter as well.
_edit_
I looked it up, hoover dam used steel pipes, not solid bars, so there's room for the corrosion to expand into the void created by the pipes.
Master craftsmen I tell ya, they think hard about that kind of stuff.
Concrete not starting to decay until 50 years has passed is the exception, not the rule.
Until there's apparently "no money" to replace the structure after its design life time. Thinking in decades of life span for many of these structures is very short sighted. I think the article mostly gets that across i.e. re-enforced concrete is hard to recycle and their life span is often within that of a human life. We should be able to do better and create large scale structures that can not only serve a purpose over several life times, but can be added to or enhanced rather than demolished.
The only reason we keep building these time limited structures is because building codes still allow this, which leads to easy short term profits, and it's "someone else's problem in 50-60 years time". There's no incentives.
It's not clear to me that the Romans knew that, or that it informed their choice of that building material. I suspect it's more that they built with what they had, and got lucky that it turns out to be incredibly durable stuff.
Also, buildings don't fall all of sudden. You would get a lot of cracks and problems before your building collapses
https://www.concretenetwork.com/concrete/demolition/urbanite...
It's definitely a case of downcycling, though: there's a lot less we can do with urbanite than with cement and aggregate in their original forms.
https://onlinelibrary.wiley.com/doi/pdf/10.1002/suco.2017001...
Some German researchers seem to think that carbon fiber-reinforced polymer "rebar" could be more durable than steel bars with similar cost and lower weight:
https://www.aboutcivil.org/carbon-reinforced-concrete-buildi...
Unfortunately, the terminology is not well standardized, and when you look up "carbon fiber reinforced concrete", you never know if you're going to get a fiber-reinforced cement composite (incorporating carbon fibers directly into the cement matrix) or a CFRP rebar system. Regardless, there do seem to be some improvements on the horizon.
Unreinforced concrete can and does last for many hundred years. Reinforced concrete, not so much.
FTA:
“Early 20th-century engineers thought reinforced concrete structures would last a very long time – perhaps 1,000 years. In reality, their life span is more like 50-100 years, and sometimes less. Building codes and policies generally require buildings to survive for several decades, but deterioration can begin in as little as 10 years.”
In first-world countries/states with earthquakes, the answer to this is often yes and yes.
A good article from 2000 in Christchurch discusses the issues: https://www.canterbury.ac.nz/media/documents/event/Hopkins-L...
The article is relevant because Christchurch had a major earthquake in 2011. I know of quite a few older buildings that were retrofitted that did not even need to be demolished (most buildings are designed to just survive a major earthquake, but often they need to be demolished due to damage, similar to writing off cars after accidents).
Christchurch did have regulatory failures because many older buildings were known to be unsafe (e.g. only meeting 10% of current code/regulations), but owners could defer fixing them up to code almost indefinitely. But that regulatory failure is being addressed in other parts of the country e.g. Wellington.
The South Island of New Zealand is overdue for a magnitude 8.2 Earthquake which will devastate many towns on the West Coast, and will affect the whole country indirectly. https://www.stuff.co.nz/the-press/news/90364889/magnitude82-...
You can sometimes see where concrete of a building has been tested for example a circular hole about 10cm across is left where a sample was taken.
If interested, next time you meet a civil engineer or someone working in the relevant department that deals with the building codes will often know relevant details about your location.
You want a flimsy shell and to externalise the environmental impact? Sure thing, whatever the market will bear and is legal.
I think it is fair enough for people to put pressure on current practices. Zara and H&M will persist, but their customers should be and, thanks to outside voices, are now aware that social and environmental factors are involved in fast fashion.
Sure, it's arbitrary. But we still have alternatives. All else being equal, less entropy is better than more.
The kind of concrete they use in buildings is not the same as the concrete they use in sidewalks.
Moreover, back in Roman times, Roman concrete was not as strong back as it is today. As the article you linked points out, "Because both minerals take centuries to strengthen concrete, modern scientists are still working on recreating a modern version of Roman cement."
A flat roof, for example, is very prone to leaking, which when not constantly taken care of will wreck the building. Another is if the roof keeps water off of the walls (how big the overhang is). Many buildings have eaves that are an inch or two. The exterior walls of these buildings won't last.
Any building on a flat area near a river is going to flood. Any building without proper drainage around it is going to rot away.
Wood shingles need constant maintenance or goodbye to the building.
The concrete and steel have different thermal expansion meaning that, over time, the concrete is bound to develop cracks if there are any changes in temperature.
Another reason why modern structures crack and disintegrate is because they tend to be built from rather large blocks. Whereas old structures were composed from single bricks or stones. The way these were built meant that the structure would crack in multiple places in a way that would allow the movement to be absorbed and distributed throughout the structure and be more easily repaired. See this guy explain it much better than I could: https://www.youtube.com/watch?v=p5qVxAoKwbE
Uhhhh the rest of the stuff in Concrete isn't great for human health, either, or as my cousin likes to say, "it sure ain't vitamins."
Quartz dust and silica sand are really bad for the lungs, likely carcinogens. Lime is caustic. Dust in general is bad to breathe.
These are well-known hazards in demolition and mitigation techniques already exist.
I've noticed manufacturing companies like big auto will try to solve for this by creating more specs for parts provided by suppliers but that's a losing battle as its always a race to the bottom. Plus now you need large testing teams to verify parts meet all these different specs. Maybe some percentage of the parts do - what do you in that case? The whole process can be a mess.
(That, BTW, is from a channel devoted to concrete made by a civil-engineering academic who specialises in the stuff https://www.youtube.com/channel/UCrvfiHNDS_QI-FgKQSmTITQ )
That claim seems to date to a particular article written in 2017 that wasn't well sourced. Roman concrete is interesting stuff and has useful properties, but humans have since created concrete mixtures that are far superior. But they're expensive, so it's not too surprising we don't see them getting used in buildings that compare less than favorably to a temple built a couple thousand years ago. Survivorship bias taken to the extreme.
I see two arguments against:
1. Future buildings will be so much better for the environment that increasing costs today for long lasting buildings or having to wait longer for environmentally better buildings is a net negative
2. Old buildings are typically not useful and so we shouldn’t encourage a future full of them (examples: smaller houses in city centres function ok but aren’t well insulated and could reduce total environmental costs of the city if they were replaced with more dense accommodation; many old churches see little use; many old buildings or rooms of them are no longer fit for any efficient purpose and so are wasting resources, eg banks with lots of space for tellers/vaults/deposit boxes or stock exchanges with big trading pits or warehouses which cannot be converted or even the rooms above shops which often seem to be disused. I have also seen other places where good use is still made of old buildings (typically long lived institutions like schools or societies or universities) though perhaps not as efficient use as might be possible. Obviously there are other cultural arguments for keeping old buildings around (but sometimes I worry regulations enforcing this can be too prohibitive, eg freezing an old building that has been changing slowly over many years at the point it becomes protected).
In a few minutes searching I didn't find any reference to required testing of old buildings for structural or materials integrity.
Construction specs often include “Allowed manufacturers” to limit your choices to certain vendors, which theoretically means you get quality material. For stainless steel, sometimes they’ll specify which alloy you need to use (304L and 316L are the most common) You certainly could submit the specified manufacturer’s product and then switch it out for a cheaper option, but if you’re caught, you could be forced to correct the work with the right material or be financially on the hook for another contractor performing the work. It would be up to someone else to notice that the steel contractor isn’t using the specified material, which may never happen.
The ‘use less of it than needed’ problem would ideally be caught by an inspector, but they certainly aren’t perfect.
Here’s a link to Cleveland Clinic’s electrical spec, if you’re curious how detailed they get: http://portals.clevelandclinic.org/Portals/57/2012_Elec%20Sp...
Japanese loathe “second hand” stuff if they can avoid it. This includes property. The service life for buildings is 47 to 50 years or so, for depreciation purposes.
Totally unrelated, but I love that 1000 year old wooden temples get rebuilt every 20 years or so[2] because of the religious idea of renewal.
[1] https://japanpropertycentral.com/2012/06/what-is-the-lifespa...
I think a good analogy world be eating healthy, you'll probably live longer then soon-to-be who doesn't eat healthy but in the end both will die and seize to exist.
Material science is incredibly interesting field and I think it will play a huge role in the future. It already does.
That doesn't tell you much: in the US the lifetime of a residential rental building is 27.5 years for depreciation purposes, and 39 for non-residential: https://www.irs.gov/publications/p946
That makes no sense. If I am buying property, it is in my best interest to make sure it isn't going to fall apart. Especially since if something happened due to my negligence, I would be responsible.
If you have no idea of whether or not the building is being inspected, why would you make the assumption it's not?
They certainly do in earthquakes. Even in areas that nominally don’t have earthquakes, some parts of the building code will surely be about ability to withstand a rare earthquake.
Their are two reasons for steel reinforcing. The steel can withstand tension and concrete can’t. Even worse concrete in tension fails catastrophically, the steel insures it fails ductally.
Masonry had exactly the same problems and all modern masonry structures are reinforced masonry...reinforced with steel, Just like concrete.
Aluminum and other potential reinforcement materials are less suited than steel because steel and concrete have similar coefficients of thermal expansion. Yes steel can corrode and expand and spall concrete. Other materials will spall concrete simply from seasonal and diurnal changes in temperature.
Concrete designs are engineered and like all engineered systems, there are trade offs between cost and performance. And like any design, use may exceed or deviate from specified design parameters.
Unless you’re talking about a very old house, this depends a lot on the local climate, construction materials, and design.
You can pretty successfully mitigate water entry with a dimple membrane and a gutter on an exposed wall, for example, and obviously this is a minimal concern if your house is in a desert.
(I’m not a trained architect, just someone interested in building science.)
My house has eaves that stick out about 2 feet. It added nothing significant to the cost, but boy what a difference it makes. The exterior walls almost never get wet. The windows and their frames stay dry and free of rot. No mildew. Haven't even needed to repaint.
There are a lot of things one can do with a house that, at trivial expense, will dramatically improve its life and lower maintenance costs.
Here's another one. Run the plumbing up interior walls. Then it won't freeze.
https://knifesteelnerds.com/2019/09/23/nitro-v-its-propertie...
But they all corrode, eventually. If you want a true corrosion-resistant metal that stays (kinda) sharp, look at one of the cobalt alloys like Stellite.
One of the reasons unreinforced concrete may last a lot longer is because its only going to exist in places that don't subject it to tensile stresses. That being said, changes like differential settling can create these stresses after construction.
'Deterioration' can mean many things in terms of concrete.
As for decay, IIUC, it loses pH gradually, from the time you mix it, and that pH is the most important protecting factor that stops the steel from rusting.
Obviously though, a lot of factors have a huge factor on lifetime, including composition, construction, environmental conditions ...
There are trade offs to everything. Build something much more durable, pay twice as much, do half the work in a season and get more complaints. We already aim to build infrastructure based on estimates of future loading - how much traffic, what kind of trucks at what weight, etc.
We'd all be much better off increasing maintenance budgets to extend the lifespan of existing structures without completely re-doing them at multiples of the current price.
All it takes is for architects and engineers to get their heads around new technologies and start specifying better materials. This wouldn't fully solve the CO2 problem of concrete, but it would reduce it by making each ton of concrete last a lot longer.
[1] https://www.owenscorning.com/en-us/composites/pinkbar-vs-ste...
[2] https://www.tuf-bar.com/5-reasons-why-you-should-use-fibergl...
[3] https://www.globalspec.com/learnmore/building_construction/b...
[4] https://www.forconstructionpros.com/concrete/equipment-produ...
If you have a two-storey house in a wet area that gets a lot of storm activity coming from the northeast, for example, and you have an exposed northeast-facing wall, the eaves aren't going to do much to shield that wall from driving rain. You'd have to make sure it's dealt with in other ways.
> Here's another one. Run the plumbing up interior walls. Then it won't freeze.
Same with this - it might be good advice in Seattle, but if I told a local builder to worry about frost mitigation where I live now (Singapore) they'd probably question my sanity.
There's epoxy-coated rebar, but that's on the way out. Quebec has already banned it. One scratch, water gets in, and corrosion starts. Also, the epoxy can be damaged by UV, like when there's a stack of rebar out in the sun.
[1] https://www.outokumpu.com/en/products/long-products/rebar
And ‘trust but verify’ is important - there are a lot of assumptions people make about what is actually checked or verified that are, well, just wrong. About a lot of things. And if you can’t find anyone saying it is happening, it very well might not be.
To the prior poster - call the NYC building department. Here is a link to their FAQ/index page and it should be straightforward to find from there. They are the ones responsible for making sure buildings don’t randomly collapse in NYC.
https://www1.nyc.gov/site/buildings/business/inspections.pag...
My 95 year old brick house would beg to differ on utility of old buildings. My prior house was over 230 years old and provided 14 years of excellent utility to me.
It’s rarely physics, almost always economics.
Texas felt the same way until February!
I work right next to a seven-storey office building in Sydney, that's built almost entirely with engineered timber - https://architectureau.com/articles/australias-first-commerc... - ever bigger and taller such buildings are going up, bit by bit, around the world.
What a weird argument. It's obvious for multiple reasons that all buildings won't fail at the same time.
That infrastructure is still useful, 20 years on.
It isn't about agility or guessing right, it's about piloting attractive technologies (eg, small-scale DSL which uses existing phonelines, which was oftentimes a reliability nightmare), and keeping an eye to the future.
cars that make many short trips, which never give the exhaust system time to fully warm up, often have extremely compromised exhaust systems, because the moisture simply can't be driven away effectively.
- dipping rebar in epoxy is sometimes done, but a single nick in the coating causes all the erosion to concentrate in that one spot, so it can be more dangerous than just uncoated rebar
- galvanised rebar works much better than epoxy, and resists corrosion at lower pH levels than normal iron, but may result in more metal loss under some conditions
- sacrificial anodes (as per the article) can and are used, but exactly how is quite complicated: if they're embedded in the concrete, the zinc breaks down into substances that can weaken it
- concrete is naturally alkaline, with cement being manufactured partly from lime, and this protects the rebar, but too high a pH causes other problems in the concrete itself, so you can't just dump alkaline substances into the mixture forever
- you can apparently use fibreglass as rebar, but I have no idea if it's any good, or what happens to fibreglass if you leave it embedded in concrete for a century
Modern concretes can do a whole lot of stuff Roman concrete can't, because there are so many formulations of it. But if you want to stick a building literally in the ocean and have it never ever disappear, nobody has shown that we can actually do it today.
There's a whole lot of theory and talk by experts, about how we don't need to make it, but if we wanted to, boy would it be easy, but don't worry, modern concrete is just so amazing, you should just use that, for modern use cases, and oh by the way, it would be too expensive to make, even though we haven't actually made it or tried to bring the price down.
There's a world of practical experience needed to claim for a fact that modern concrete is legitimately better, much less that we can actually make it and that it would hold up as we expect. I'm still waiting for concrete evidence.
UK also has a history of major failured in construction practices and inspection, where chunks of a new apartment block suddenly collapse like in Ronan Point, or a recently renovated tower block goes up in flames and half of residents die despite them warning about issues for years.
I wish living in first world country guaranteed sensible things are happening, but it doesn't
https://www.theguardian.com/environment/damian-carrington-bl... https://en.wikipedia.org/wiki/Ronan_Point https://en.wikipedia.org/wiki/Grenfell_Tower_fire
https://www.nature.com/news/seawater-is-the-secret-to-long-l...
Sounds like they knew.
Saving a little on the upfront cost only to pay a lot more for maintenance is a false economy. Stainless steel rebar does not double the cost of construction, and neither does high quality concrete.
We need to stop buying subscribtion to "bridge as a service"
Btw were Deloreans pretty rust resistant? How will the cyber truck do living by the beach?
"A recent innovation in the Japanese real estate industry to promote home ownership is the creation of a 100-year mortgage term. The home, encumbered by the mortgage, becomes an ancestral property and is passed on from grandparent to grandchild in a multigenerational fashion. We analyze the implications of this innovative practice, contrast it with the conventional 30-year mortgage popular in Western nations and explore its unique benefits and limitations within the Japanese economic and cultural framework." The 100-year Japanese residential mortgage: An examination (1995) (https://www.sciencedirect.com/science/article/abs/pii/106195....)
You have it exactly backwards - most of the budget goes to capital construction - replacement of existing structures and roads. The maintenance budget is constantly shrunk.
>Stainless steel rebar does not double the cost of construction, and neither does high quality concrete.
Last I checked stainless rebar was ~3x the cost of regular rebar...
"high quality" concrete doesn't mean anything. Most concrete is high quality.
>We need to stop buying subscribtion to "bridge as a service"
All infrastructure requires maintenance and eventual replacement. Bridges will never be permanent and will always require regular inspection, maintenance, etc.
When I asked the real estate agent what's the expected lifespan of a house, she looked at me like she's just seen an alien. In fact, half the time, they don't even get the floor space right and every floor plan comes with a disclaimer "maybe this is wrong"
But it's 5-10% of the total building cost, and if you bump that to 20% the corrosion goes from "always' to "probably never"
[1]https://www.thelocal.se/20160324/sweden-limits-mortgage-loan...
But you're not wrong in general. There will still be corrosion in the concrete eventually but less likely from rebar oxidation.
One exception is the mandatory retrofit programs implemented by some cities like San Francisco and Los Angeles.
That said, I can almost guarantee the specs for automotive manufacturers are less strict and the penalties less severe simply because the specs are made to be cost-centric rather than performance-centric.
/Acey
Physics, economics, and bureaucratics is a good summary of structural engineering. The last one can’t be ignored.
But then again so is stainless steel rebar and carbon fibre rebar and most of these other types of products because they lack ductility
And I have a friend who lives in Texas. The pipes in the outer walls froze and burst, the ones in the inner walls did not.
Jeez, of course one pays attention to the local climate. I don't worry about tornadoes in Seattle, but would if in the midwest.
This description is fairly accurate. The CaCO3 (used as a source of calcium in the cement component of concrete) is completely decarbonated in a 1450°C kiln in the process of cement manufacture, combined with silica (from shale) +/- SO4 (from gypsum) and sintered to form an anhydrous calcium silicate (clinker: e.g. tricalcium silicate, Ca3SiO5, ‘alite’), then powdered (e.g. ordinary Portland cement, OPC). The skeletal limestone is long gone — and the above decarbonation step is the reason cement manufacturing process is a significant GHG source (in addition to fuel consumption by the kiln itself).
Mixing water with the powdered clinker generates a very rapid, exothermic, partial dissolution of the primary silicate. The rapid release of silica results in nucleation and growth of calcium silicate hydrate (CSH) plus Ca(OH)2. CSH binds the remaining unreacted solid mass together, giving cement its durability and strength.
Also, due to a lack of reinforcement, Roman concrete structures, at least those that survived, avoided putting concrete in tension. Roman concrete won't last very long in areas of buildings that are under tension. Edit: the implication being that using Roman concrete would make many modern building designs unworkable, particularly taller thinner designs that sway a bit in the wind.
Believe it or not, this kind of thing isn't just immediately obvious to everyone.
What needs intervention is to find a suitable replacement for concrete/cement citing it's increasing contribution to global warming.
Doesn't change the building process at all, just where they procure from.
I'm sure stainless rebar is easy to make. We could turn out huge amounts of it. But I don't see it ever having the same useful properties. All manner of stainless I've worked with is incredibly stiff and hard compared to regular steel. It's actually desirable in most applications, but rebar in particular needs to be flexible.
The bigger difference in components is the kind of cement the Romans (and we "moderns" until a few years ago) used, i.e. pozzolanic cement, nowadays everything is "portland" cement.
BUT the definite difference is the kind of structures, Romans did not use "reinforced" concrete, only various types of "plain, non-reinforced" concrete, and all their structures are based on the main characteristic of concrete, which is its resistance to compression.
The idea of reinforced concrete is all about adding to a material with excellent compression resistance (but no resistance on tension/traction) a material (steel) with excellent resistance to tension/traction and relatively poor (in the quantities used in reinforced concrete) resistance to compression, obtainining a composite material that excels in both.
About ashes, overall it is more about their size that about their nature, concrete is a composite and if you have all possible sizes of aggregates (ashes are very, very small sized particles) in the "right" amount you essentially fit "better" the space, i.e. you have a higher density of the resulting composite, and, particularly when compression resistance is the goal, the higher the density the better the resistance.
Imagine (say) that you have to fill a 100x100x100 mm box with 10 mm balls, you can fit in them a certain amount of these balls (roughly 10x10x10=1000), but you are leaving lots of "air" between them, a single 10 mm ball is 2/3x3.1416x5^3=262 mm3, so the 1000 balls total 262,000, but the volume of the box is 100x100x100= 1,000,000, now if you have some 2 mm balls you can add them in the same volume, and then if you have some 0.5 mm balls you can put some of them in that same box as well, etc.
I don't think this stops these new products from being used, it's just another engineering tradeoff.
I contend that buildings, with a few exceptions, are consumables. Whether wise or not, humans like to build new things, customizable to their own tastes.
An office building that lasts ‘only’ 50 years instead of 500 shouldn’t be surprising. In 50 years time, for most buildings, even if it could last another few decades, it will be torn down and replaced. That’s just what humans do. States differently, even if everyone at the time knew concrete/rebar would only last 50 years and not the 1000+ years, it wouldn’t have made a difference, for nobody — short of a Pharaoh — has any interest in such a permanent structure. Cities come and go, buildings come and go, rivers and shorelines change, etc. it’s not reasonable to assume the desirable center of activity (either residential or commercial) in which one builds will even be there 50 years hence. So why worry about how long the building will last?
False.
Large structural failures can be catastrophic and unexpected.
Buildings can and do collapse quite suddenly. The examples here are not necessarily caused by reinforced concrete failures (though several cases make use of reinforced concrete --- generally other failures lead to the collapse). But the final failure of a system under load and near its structural limits can be quite sudden.
Taiwan bridge: https://youtube.com/watch?v=OSCPUGHUyIs https://youtube.com/watch?v=WqHXMswLwPM
Minnesota I35W bridge collapse: https://youtube.com/watch?v=CMdv2wRaqo4
Jerusalem dance floor: https://youtube.com/watch?v=5UOb7RBWlak
Morandi bridge, Italy: https://youtube.com/watch?v=V479srTBlAk
Hard Rock Hotel New Orleans (under construction): https://youtube.com/watch?v=WC8k5unvyfU
Sampoong Department Store, Korea (visualisation): https://youtube.com/watch?v=aQXTSR9koCg
The Kansas City Hyatt Regency skywalk collapse (1981) would be another instance. I don't believe there's video of the failure itself, though Grady from Practical Engineering has a great explainer of what went wrong: https://youtube.com/watch?v=VnvGwFegbC8