12 ms·

The problem with reinforced concrete

288 points by danfru 10y ago

jpt4 10y ago
An alternative to steel for concrete reinforcement is glass blown basalt [0], which struck my interest via its use in a project for free-floating, (geopolymer) concrete seasteading vessels [1]. [0] http://basalt-rebar.com/ http://basalt-rebar.com/ [1] https://www.reddit.com/r/Floathouse/ https://www.reddit.com/r/Floathouse/
- danieltillett 10y ago
  That basalt rebar is very interesting - what is the cost compared to steel?
  - jpt4 10y ago
    I am afraid I don't know specifics. For a while the only suppliers were non-American (primarily Russian), so the market prices were not equitably comparable. /r/floathouse (link [1]) will have up to date information.
    - krasin 10y ago
      Interesting. I've made a quick search over Runet, it seems that basalt / basalt-plastic rebar is in large-scale production: http://nano-sk.ru/stekloplastikovaya-armatura/bazaltovaya/ http://nano-sk.ru/stekloplastikovaya-armatura/bazaltovaya/ They claim it's better and cheaper than steel rebar. No word about disadvantages, which I assume exist (edit: found, see below). Edit. Oh, they carry a price: http://nano-sk.ru/price-list/ http://nano-sk.ru/price-list/ -- 1m of d=14mm rebar costs ~$0.60. But I don't know the price for the regular steel rebar, though :) Edit2. There's a list of disadvantages here (sorry, in Russian): http://www.tdbazalt.com/category/materiali_dlia_stroitelstva_i_otdelki/armatura_stekloplastikovaya/nedostatki_stekloplastikovoi_armaturi_minusi/ http://www.tdbazalt.com/category/materiali_dlia_stroitelstva... 1. Can't stand high temperature, as basalt rebar has polymer as a binder for basalt fiber. 2. Can bend easier than steel; will break easier than steel 3. Can't stand alkaline environment (there're claims that some newer types of the basalt rebar don't carry this issue)
  - emilong 10y ago
    No idea on the accuracy of this, but this article claims there's a company (http://www.neuvokascorp.com/ http://www.neuvokascorp.com/) making basalt rebar at the same price as steel: http://cleantechnica.com/2014/11/06/neuvokas-basalt-rebar-lighter-stronger-cost-steel/ http://cleantechnica.com/2014/11/06/neuvokas-basalt-rebar-li...
- HillaryBriss 10y ago
  That's really interesting. There are a lot of advantages to this kind of rebar apparently. The website also says: > Basalt rebar does not conduct electricity Which got me thinking about electrical codes. In some cases, a concrete building's electrical wiring system uses the rebar in the concrete structure as an electrical ground. But, I guess for buildings constructed with basalt rebar, conductive copper rods would have to be specifically built in separately, for purposes of electrical grounding.
greydius 10y ago
The only salient point this article mentions (but only briefly) is that concrete production generates a huge amount of CO2. Everything else is hogwash. In terms of strength, versatility, and cost, steel-reinforced concrete has proven to be the greatest building material humans have ever devised. It is by no means perfect, but nothing is. Concrete needs to be maintained just like anything else. With neglect it decays.
- paganel 10y ago
  I'm a fan of brutalism, so I do like concrete buildings and find them interesting, but there's also a good case to be made about mud bricks, which the author aludes to. Yes, you'll have issues building 10-storey high buildings out of mud-bricks, but it's definitely possible to build structures (like barns) out of them that can easily last more than 100 years, without the builder having to have a civil engineering degree. I've seen one such structure with my one eyes, built by my grand-grand-father who was a peasant. The only thing you have to be careful about when building stuff out of earth is water infiltrations, otherwise you're good. Buildings made out of earth are also better heat insulators compared to concrete. My grandma's house was always cool in the summer, while my appartment which is part of a building made out of concrete wouldn't be livable in the summer without AC.
  - greydius 10y ago
    That's an apples to oranges comparison, though. Mud bricks are a good building material, and so are a lot of other things (e.g. wood, bamboo, paper), when the structure only has to support itself and a roof. But concrete enables structures that cannot (or should not) be built with those materials.
  - lisivka 10y ago
    Mud/clay walls are OK to support roof or act as insulator, but they are weak when you need to attach something to wall. Moreover, outer layers can laminate out of wall if they are stronger than wall itself, so you will need to use lime stucco to paint wall, which is soft enough. To solve these problems with mud/clay walls, wood and straw are used. To date, G.R.E.B.[1] technology is most advanced, cheap, and easy to use. [1] http://www.approchepaille.fr/pdf/straw-bale-building-greb.pdf http://www.approchepaille.fr/pdf/straw-bale-building-greb.pd...
dkbrk 10y ago
This article has many problems. Most importantly, building techniques such as "steel frame", "traditional bricks and mortar", "mud brick" and "rammed earth" are far less capable than reinforced concrete. The article implies that as these are more "durable" they are superior to reinforced concrete. This is a false equivalence of staggering magnitude. Reinforced concrete is the great enabler of modern high-rise construction and civil engineering; most projects simply would not be able to be built without reinforced concrete. Without reinforced concrete the world would be a very different place. I take special issue with the article's use of pseudoscientic false analogies. > This means that concrete structures, for all their stone-like superficial qualities, are actually made of the skeletons of sea creatures ground up with rock. It takes millions upon millions of years for these sea creatures to live, die and form into limestone. This timescale contrasts starkly with the life spans of contemporary buildings. This is utter drivel. There is a valid point in that for smaller scale constructions other techniques may be applicable which are otherwise ignored; also that there are alternatives to steel as the reinforcing material, both for prestressed structures and not.
- euroclydon 10y ago
  I read an engineering guideline on concrete that I wish I could find. It compared the economics of building a steel vs reinforced concrete bridge. Steel came out better when you considered the lifetime and especially the recyclability, but concrete was cheaper to build initially. The steel bridge would last indefinitely, as long as you kept it painted, or even replaced rusted parts. Reinforced concrete is costly to demolish, and nearly impossible to recycle. Crushed concrete can be used as a filler, but in order to be used for fresh concrete it must be free of contaminates, which is rarely the case, and no one wants to risk the integrity of a new structure of any importance. The percentage of all concrete structures even built, that are still standing must be quite large. This will not be a great legacy to leave future generations.
- jessaustin 10y ago
  We're not running out of limestone anytime soon, but otherwise this is a bit off-target. All of the alternative construction techniques you mention have advantages over reinforced concrete. Concrete also has its advantages, but TFA is not wrong about the disadvantages. When I traveled to Philippines earlier this year I was struck by how they use masonry in situations that in USA would be reinforced concrete. Granted, the blocks are all CMUs, but the technique is masonry. I think it's because very few roads (at least in the places I traveled) would be suitable for standard 6-yard concrete trucks, whereas you can always throw a few dozen blocks on the back of a motorcycle. Of course labor costs are also a factor. However, concrete in block form is totally recyclable, while as TFA notes when poured it is not.
reidacdc 10y ago
The very first sentence of this article is a giant red flag, the comparison between the Pantheon in Rome and modern concrete is deeply misleading -- Roman concrete was a different material than modern Portland-cement/sand/gravel scheme, it had better resistance to cracking and could set under water. [1] The rest of the article seems to be, if you think on different time-scales and use different cost-benefit criteria (e.g. include or exclude environmental effects), you get different answers about the suitability of various materials. This is indisputably true. [1] https://en.wikipedia.org/wiki/Roman_concrete https://en.wikipedia.org/wiki/Roman_concrete
- wiredfool 10y ago
  Modern concrete can set underwater, and, at least for concrete where you care about the results, you want to keep the surface wet until the concrete cures appropriately. (IANAPE, but I took a grad level concrete course in school) addition/edit: Quick primer. When concrete cures, it's a chemical process that converts free water into an electrostatic gel in the cement crystals. That interlocks the small and large aggregate to make a solid. If concrete dries rather than cures, then that gel doesn't form and you don't get the gel holding it together. If you heat up cured concrete enough, you'll drive out the water and make it a powder again. If you cure something under water, it can technically continue to cure for a very long time. Normally you keep it moist for 24-48 hours, and standard testing is done at 28 days. That will get you something like 90% of the final strength, if it can continue to cure indefinitely. I've tested concrete that was semi-submerged for 40 years where the design strength was 4ksi, and it tested out at 14ksi.
RP_Joe 10y ago
China has Fiberglass REbar : https://www.alibaba.com/showroom/fiberglass-reinforcing-bar.html https://www.alibaba.com/showroom/fiberglass-reinforcing-bar....
- lisivka 10y ago
  Fiberglass does not bend like steel. It will crack instead, which may lead to catastrophic result.
jhallenworld 10y ago
I'm interested in the long term durability of pre-stressed concrete- in its case the reinforcement is critical.
fpaboim 10y ago
I'm a civil engineer. This is bullshit. Reinforced concrete uses much less concrete because, well, you have rebar to take care of tensile stresses and concrete does well with compression so it's much more efficient, which is basic. Also, and a very important point, reinforced concrete (in general) tends to fail in non-catastrophic ways making it safer to use and easier to spot conceptual errors in the project and building process. Reinforced concrete can also be recycled, the concrete becomes structural blocks (I even worked with these before) and the rebar is steel so thats easily recycleable too. In the end, it's cheap and affordable so you can build much more with reinforced concrete than with concrete reinforced with carbon fiber which would last forever but would cost a fortune (this can also be used to reinforce reinforced concrete...) making housing unaffordable to a large part of the world. Do you also really want to spend that much more to make a project to last 500 years without using reinforced concrete? You know that goes into the equation when engineers project strucures right? Oh well, clickbait.
- guard-of-terra 10y ago
  Just moved into an apartment that's 116 years old. I'm just so happy that people had different perspective back then. It's sad that we don't understand - unsustainable growth, scaffolding and prototyping phase is long overdue.
  - learc83 10y ago
    People didn't have a different perspective back then. It's just survivorship bias. People built plenty of crappy disposable buildings 116 years ago, you just don't see them because they were crappy disposable buildings built 116 years ago.
  - madengr 10y ago
    My house, currently not there but still own it, is 173 years old. Though that's common in eastern US.
    - ghaff 10y ago
      Mine is just under 200 years old--also in the eastern US. It would be pretty silly though to view my house as this incredible structure that a farmer built 200 years ago to last for the ages. The fieldstone foundation is original as are various posts and beams. But the house has been expanded, rebuilt, updated, etc. in all manner of ways since it was built.
3pt14159 10y ago
I used to be structural engineer, and while things may have changed in the past 8 years since I left, I doubt it. The problem with structural engineering is incentives. It is one of the reasons that I left. Most structural engineering companies are filled with conservative, boring engineers that prefer to look up pre-designed segments and don't make full use of the steel design handbook or building codes. For example, in Canada if you have a non-load bearing brick outer face (most brick buildings in Canada) you're allowed to reduce the wind load by 10%. I was the only person I knew that knew this because I actually read the steel, concrete, and wood design handbooks front to back while I made notes. Furthermore almost nobody has read the building code "just because" they might hop to a section here or there when they need it, but they're generally not going to just sit down and read the thing. So when I would design buildings I would be able to take advantage of a lot more things than most people. This lead to my buildings being cheaper / easier to build, which of course lead to our engineering fees looking like a larger portion of the job. The problem with reinforced concrete is the same. Engineers have no financial incentive to make alterations to their designs to make the buildings last longer. It is almost trivial to make sure steel wont rust (or to double or triple a buildings life) but it makes construction costs go up 0.01% and makes engineerings fees go up 0.1% so nobody does it. Regulators are to blame too. There are amazing concretes (Ultra High Performance Concretes) we should be using in our buildings that completely lack even needing steel because they are so ductile and strong (MPa 200 for the one I was familiar with, Ductal by Lafarge), but it's impossible to use in construction in Canada because the code is so rigid.
- colanderman 10y ago
  > Most structural engineering companies are filled with conservative, boring engineers that prefer to look up pre-designed segments and don't make full use of the steel design handbook or building codes. I dare say the same is true of software engineering. I, nominally a backend engineer, know (and apply) more about HTTP than most front-end devs and architects I've met, simply because I sat down one day and read the HTTP spec. (It's not a difficult read!)
  - sitkack 10y ago
Eric_WVGG 10y ago
This reminded me of a bit from 2014 where some researchers claim to have rediscovered the Roman's particular recipe for long-lasting concrete. http://www.pnas.org/content/111/52/18484.abstract http://www.pnas.org/content/111/52/18484.abstract For laypersons http://www.dailymail.co.uk/sciencetech/article-2877547/Why-Colosseum-hasn-t-collapsed-Roman-concrete-used-secret-ingredient-stand-test-time-engineers-want-copy-it.html http://www.dailymail.co.uk/sciencetech/article-2877547/Why-C...
guard-of-terra 10y ago
Where I live there's a huge number of apartment blocks, most of them built in 60s and onwards, and the apartments are the sole place to live and the prime asset for most people. They'll definitely start crumbling in a few decades and not many people will be able to afford a new home as well as deprecation of their main asset. Have no idea how this might ever resolve, frankly.
- Spooky23 10y ago
  NYC will have fun times with this problem. They have thousands of mid rise public housing projects built from 1945-1975.
  - guard-of-terra 10y ago
    In NYC at least most apartments aren't owned by tenants (are they?). So it'll be landlords' problems.
Lagged2Death 10y ago
The depressing counterpoint, I suppose, is that 99% of the time, you're not building the Pantheon, you're building something that was intended to be minimally-acceptable, utilitarian, and disposable from the get-go: a parking garage, a tilt-up big-box building, a freeway on-ramp, a strip mall. All of which may well be obsolete in a few decades just because the urban environment changes rapidly. If you could figure out a systematic way to cut the cost and the lifetime of such lowbrow, mass-produced concrete structures in half, developers wouldn't hesitate, they'd jump on it immediately. We revere longevity only in retrospect.
- keithpeter 10y ago
  Most of the big-box buildings I've seen in UK recently are steel frame/breeze block/metal cladding structures on a poured concrete base. The idea being you can basically unbolt the walls when you want to take it down.
- fsloth 10y ago
  I don't see expendability necessarily as a downside - if the system would support lifetime learning of experts. Building and rebuilding the same thing again and again should be a good way to learn how to make it as good as it can be from design and construction point of view. The problem is if the system does not cherish and support this opportunity to learning and mastery - which many for-profit commercial establishments sadly don't.
bane 10y ago
This article makes an interesting comparison to ancient Roman concrete. While the Romans built a tremendous amount of infrastructure in concrete, survivorship bias means that the few bits that have hung around are seen as some sort of superior quality to Roman understanding of concrete. However, if you go to Rome, most of the surviving bits are millions upon millions of stacked and mortared bricks, and most of what has survived are uninteresting walls. [1] For some reason, our collective memory of Roman ruins is that they're all aged concrete or stone. But when in Rome, you end up seeing lots of this [2], which when built probably had a layer of facade material on it. And it makes sense, stacked, weather resistant, often covered in a prettier facade, baked bricks should last more or less forever until the elements wear them down. The widespread reintroduction of concrete as a building material really didn't happen until around the turn of the 20th century. And reinforced concrete didn't find widespread use until a few decades after that. Not particularly confusing, the first generations of buildings built with these fairly new and only partially understood materials are the buildings that the author is mostly writing about. The real culmination of exposed, reinforced-concrete-everywhere, finally happened in the 50s with the advent of the eye cancer called brutalism. Today a tremendous number of brutalist buildings today are absolutely falling apart, and I blame that on a lack of understanding of how reinforced concrete should be used and the availability of more modern materials and perhaps an overenthusiasm and misuse of materials where they shouldn't have been. But still, if we fast forward a thousand years, there's bound to be a percentage of those structures still around and survivorship bias in the future will lead some to speculate that the engineers of the 20th century were geniuses unrivaled by any in the future. 1 - http://previews.123rf.com/images/13th/13th0902/13th090200009/4338560-damaged-brick-walls-in-the-ancient-Roman-city-Pompeii--Stock-Photo.jpg http://previews.123rf.com/images/13th/13th0902/13th090200009... 2 - http://farm6.staticflickr.com/5185/5762585618_10a11f5a38_z.jpg http://farm6.staticflickr.com/5185/5762585618_10a11f5a38_z.j...
- Retric 10y ago
  More realisticly zero steel reinforced concrete structures will survive, but other types of buildings might. The house I grew up in for example is pushing 300 years old. That's still a long way to go, but the older it gets the more likely it is to be preserved. A 90% chance it survives any given 50 years = 2-3% chance it makes 1900.
wilsonfiifi 10y ago
I haven't been a practicing engineer since 2007 but if my memory serves me well, to avoid problems of corrosion one often used method was to increase the cover [0](distance from concrete surface to top of steel reinforcement using spacers). I can't see it mentioned anywhere in the article, will probably have to re read it... [0] http://www.buildinghow.com/en-us/Products/Books/Volume-A/The-construction/Reinforcement-Specifications/Concrete-cover http://www.buildinghow.com/en-us/Products/Books/Volume-A/The...
- schiffern 10y ago
  As both the partial pressure of CO2 in the air and the concrete temperature rises due to climate change, the depth of carbonatation (the process that lowers pH and initiates rebar corrosion) is expected to increase by 45% by 2100 under the A1FI "business as usual" emission scenario. So expect to hear more about this problem in the future. http://www.cipremier.com/e107_files/downloads/Papers/100/37/100037012.pdf http://www.cipremier.com/e107_files/downloads/Papers/100/37/...
nusq 10y ago
This article is full of FUD. What is the alternative? All these reinforced concrete problems are well understood and studied. if proper construction and design codes and maintenance guidelines are followed these structures can last a very long time. In europe we have EuroCodes that account for this problems and to my knowledge concrete cancer is not related with steel corrosion but with a long term chemical reaction between some aggregates and cement. Remember that concrete is cement with sand and stones and the hardning chemical reactions are complex and can last for decades.
- schiffern 10y ago
  >to my knowledge concrete cancer is not related with steel corrosion but with a long term chemical reaction between some aggregates and cement. It's called carbonatation, it reduces the concrete's pH which leads to rebar failure, and it's only going to get worse with climate change. https://en.wikipedia.org/wiki/Carbonatation https://en.wikipedia.org/wiki/Carbonatation
  - nusq 10y ago
    I was refering to alkali-silica reactions https://en.wikipedia.org/wiki/Alkali%E2%80%93silica_reaction?wprov=sfla1 https://en.wikipedia.org/wiki/Alkali%E2%80%93silica_reaction...
    - schiffern 10y ago
      Thanks, TIL!
schiffern 10y ago
Surprised they didn't mention carbonatation and climate chance. tl;dr rising partial pressure of CO2 in the air leads to a spontaneous "reverse calcination" process, lowering the pH which leads to rebar failure. By 2050 most reinforced concrete buildings will be effected. https://www.bostonglobe.com/ideas/2014/10/11/for-concrete-climate-change-may-mean-shorter-lifespan/rJ8vWjSp2xRShwFmDS6lQJ/story.html https://www.bostonglobe.com/ideas/2014/10/11/for-concrete-cl... https://en.wikipedia.org/wiki/Carbonatation https://en.wikipedia.org/wiki/Carbonatation http://ec.europa.eu/environment/integration/research/newsalert/pdf/246na2_en.pdf http://ec.europa.eu/environment/integration/research/newsale...
ChrisNorstrom 10y ago
Didn't epoxy coated steel rebar solve the problem of rust and "concrete cancer" https://www.youtube.com/watch?v=QWUpMWJtgvc https://www.youtube.com/watch?v=QWUpMWJtgvc It's pretty much the standard now.
jorblumesea 10y ago
The real question is do we want buildings to survive 200 years? In 200 years building technology might have advanced far enough that everything is carbon fiber concrete or something far superior. People look at degradation of a structure as some kind of serious issue, but it can also be seen as a positive.
- syphilis2 10y ago
  To expand on this, will our descendants have the same demands in 200 years? Will a revolution in transportation dramatically change infrastructure needs? What will employment look like, how will businesses operate? Will citizens want the structures we build in the locations we build them? The author suggests we build structures to stand the test of time and addresses structural, economic, and environmental needs, but not societal ones. The Moai referenced are not artifacts because they weren't engineered well enough, they're artifacts because they outlived the societies that built them.
foxhop 10y ago
Research "rammed earth" and "earth ships" for details on why old structures last longer. Rammed earth has great thermal mass which has huge benifits if controlled.
etatoby 10y ago
I see a lot of engineers calling the article FUD and BS, what with it mentioning ancient Roman buildings and mud bricks. I also see several commenters (myself included) wholeheartedly agreeing with the point it makes. I think bluthru hit the nail on the head somewhere below (which will soon be above?) > The point is that longer-lasting structures should be cheaper, but because we don't factor in environmental harm and lifecycle cost into the price of things we end up with cheap buildings that exist to generate ROI ASAP. Factoring in those kinds of costs runs contrary to mainstream economic doctrine, so the question really is whether you think that capitalism (in its current form) is doing more harm than good for our communities and/or for our species as a whole, especially including future generations. Do you?
- ams6110 10y ago
  Cheap building to generate ROI ASAP sounds a lot like MVP to me. And MVP is what everyone here advises.
combatentropy 10y ago
I like the look of brick. It lasts a long time too. Why don't we use it more?
- Spooky23 10y ago
  High labor costs. Also the postwar construction boom dominated by big projects killed the industry for higher end brick.
  - TheCowboy 10y ago
    The high labor costs also resulted in brick masonry becoming a basically lost art. There was a building a few blocks away from where I used to live, where a car crash had led to a catastrophic collapse of a circular structural brick tower. It was an eye sore for years and years. The owners apparently couldn't find the skills to repair it for a long. The repair looks great but doesn't perfectly match. Even with the hassle, structural brick buildings are great.
- colin_mccabe 10y ago
  At least in California, we don't use it because brick buildings crumble in earthquakes. http://www.latimes.com/local/lanow/la-me-ln-quake-safety-thousands-of-brick-buildings-still-not-retrofitted-20140826-story.html http://www.latimes.com/local/lanow/la-me-ln-quake-safety-tho... In new construction, you can use it as a facade, but not for anything structural (to oversimplify a bit.) Elsewhere in the US, brick would probably be a good choice, but it's more expensive than slapping together another bargain-basement wood-frame house. On the other hand, for some reason, Europe has a lot of brick buildings and even still puts in brick streets sometimes.

288 points by danfru 10y ago

jpt4 10y ago

An alternative to steel for concrete reinforcement is glass blown basalt [0], which struck my interest via its use in a project for free-floating, (geopolymer) concrete seasteading vessels [1]. [0] http://basalt-rebar.com/ http://basalt-rebar.com/ [1] https://www.reddit.com/r/Floathouse/ https://www.reddit.com/r/Floathouse/

danieltillett 10y ago
That basalt rebar is very interesting - what is the cost compared to steel?
- jpt4 10y ago
  I am afraid I don't know specifics. For a while the only suppliers were non-American (primarily Russian), so the market prices were not equitably comparable. /r/floathouse (link [1]) will have up to date information.
  - krasin 10y ago
    Interesting. I've made a quick search over Runet, it seems that basalt / basalt-plastic rebar is in large-scale production: http://nano-sk.ru/stekloplastikovaya-armatura/bazaltovaya/ http://nano-sk.ru/stekloplastikovaya-armatura/bazaltovaya/ They claim it's better and cheaper than steel rebar. No word about disadvantages, which I assume exist (edit: found, see below). Edit. Oh, they carry a price: http://nano-sk.ru/price-list/ http://nano-sk.ru/price-list/ -- 1m of d=14mm rebar costs ~$0.60. But I don't know the price for the regular steel rebar, though :) Edit2. There's a list of disadvantages here (sorry, in Russian): http://www.tdbazalt.com/category/materiali_dlia_stroitelstva_i_otdelki/armatura_stekloplastikovaya/nedostatki_stekloplastikovoi_armaturi_minusi/ http://www.tdbazalt.com/category/materiali_dlia_stroitelstva... 1. Can't stand high temperature, as basalt rebar has polymer as a binder for basalt fiber. 2. Can bend easier than steel; will break easier than steel 3. Can't stand alkaline environment (there're claims that some newer types of the basalt rebar don't carry this issue)
- emilong 10y ago
  No idea on the accuracy of this, but this article claims there's a company (http://www.neuvokascorp.com/ http://www.neuvokascorp.com/) making basalt rebar at the same price as steel: http://cleantechnica.com/2014/11/06/neuvokas-basalt-rebar-lighter-stronger-cost-steel/ http://cleantechnica.com/2014/11/06/neuvokas-basalt-rebar-li...
HillaryBriss 10y ago
That's really interesting. There are a lot of advantages to this kind of rebar apparently. The website also says: > Basalt rebar does not conduct electricity Which got me thinking about electrical codes. In some cases, a concrete building's electrical wiring system uses the rebar in the concrete structure as an electrical ground. But, I guess for buildings constructed with basalt rebar, conductive copper rods would have to be specifically built in separately, for purposes of electrical grounding.

greydius 10y ago

The only salient point this article mentions (but only briefly) is that concrete production generates a huge amount of CO2. Everything else is hogwash. In terms of strength, versatility, and cost, steel-reinforced concrete has proven to be the greatest building material humans have ever devised. It is by no means perfect, but nothing is. Concrete needs to be maintained just like anything else. With neglect it decays.

paganel 10y ago
I'm a fan of brutalism, so I do like concrete buildings and find them interesting, but there's also a good case to be made about mud bricks, which the author aludes to. Yes, you'll have issues building 10-storey high buildings out of mud-bricks, but it's definitely possible to build structures (like barns) out of them that can easily last more than 100 years, without the builder having to have a civil engineering degree. I've seen one such structure with my one eyes, built by my grand-grand-father who was a peasant. The only thing you have to be careful about when building stuff out of earth is water infiltrations, otherwise you're good. Buildings made out of earth are also better heat insulators compared to concrete. My grandma's house was always cool in the summer, while my appartment which is part of a building made out of concrete wouldn't be livable in the summer without AC.
- greydius 10y ago
  That's an apples to oranges comparison, though. Mud bricks are a good building material, and so are a lot of other things (e.g. wood, bamboo, paper), when the structure only has to support itself and a roof. But concrete enables structures that cannot (or should not) be built with those materials.
- lisivka 10y ago
  Mud/clay walls are OK to support roof or act as insulator, but they are weak when you need to attach something to wall. Moreover, outer layers can laminate out of wall if they are stronger than wall itself, so you will need to use lime stucco to paint wall, which is soft enough. To solve these problems with mud/clay walls, wood and straw are used. To date, G.R.E.B.[1] technology is most advanced, cheap, and easy to use. [1] http://www.approchepaille.fr/pdf/straw-bale-building-greb.pdf http://www.approchepaille.fr/pdf/straw-bale-building-greb.pd...

dkbrk 10y ago

This article has many problems. Most importantly, building techniques such as "steel frame", "traditional bricks and mortar", "mud brick" and "rammed earth" are far less capable than reinforced concrete. The article implies that as these are more "durable" they are superior to reinforced concrete. This is a false equivalence of staggering magnitude. Reinforced concrete is the great enabler of modern high-rise construction and civil engineering; most projects simply would not be able to be built without reinforced concrete. Without reinforced concrete the world would be a very different place. I take special issue with the article's use of pseudoscientic false analogies. > This means that concrete structures, for all their stone-like superficial qualities, are actually made of the skeletons of sea creatures ground up with rock. It takes millions upon millions of years for these sea creatures to live, die and form into limestone. This timescale contrasts starkly with the life spans of contemporary buildings. This is utter drivel. There is a valid point in that for smaller scale constructions other techniques may be applicable which are otherwise ignored; also that there are alternatives to steel as the reinforcing material, both for prestressed structures and not.

euroclydon 10y ago
I read an engineering guideline on concrete that I wish I could find. It compared the economics of building a steel vs reinforced concrete bridge. Steel came out better when you considered the lifetime and especially the recyclability, but concrete was cheaper to build initially. The steel bridge would last indefinitely, as long as you kept it painted, or even replaced rusted parts. Reinforced concrete is costly to demolish, and nearly impossible to recycle. Crushed concrete can be used as a filler, but in order to be used for fresh concrete it must be free of contaminates, which is rarely the case, and no one wants to risk the integrity of a new structure of any importance. The percentage of all concrete structures even built, that are still standing must be quite large. This will not be a great legacy to leave future generations.
jessaustin 10y ago
We're not running out of limestone anytime soon, but otherwise this is a bit off-target. All of the alternative construction techniques you mention have advantages over reinforced concrete. Concrete also has its advantages, but TFA is not wrong about the disadvantages. When I traveled to Philippines earlier this year I was struck by how they use masonry in situations that in USA would be reinforced concrete. Granted, the blocks are all CMUs, but the technique is masonry. I think it's because very few roads (at least in the places I traveled) would be suitable for standard 6-yard concrete trucks, whereas you can always throw a few dozen blocks on the back of a motorcycle. Of course labor costs are also a factor. However, concrete in block form is totally recyclable, while as TFA notes when poured it is not.

reidacdc 10y ago

The very first sentence of this article is a giant red flag, the comparison between the Pantheon in Rome and modern concrete is deeply misleading -- Roman concrete was a different material than modern Portland-cement/sand/gravel scheme, it had better resistance to cracking and could set under water. [1] The rest of the article seems to be, if you think on different time-scales and use different cost-benefit criteria (e.g. include or exclude environmental effects), you get different answers about the suitability of various materials. This is indisputably true. [1] https://en.wikipedia.org/wiki/Roman_concrete https://en.wikipedia.org/wiki/Roman_concrete

wiredfool 10y ago
Modern concrete can set underwater, and, at least for concrete where you care about the results, you want to keep the surface wet until the concrete cures appropriately. (IANAPE, but I took a grad level concrete course in school) addition/edit: Quick primer. When concrete cures, it's a chemical process that converts free water into an electrostatic gel in the cement crystals. That interlocks the small and large aggregate to make a solid. If concrete dries rather than cures, then that gel doesn't form and you don't get the gel holding it together. If you heat up cured concrete enough, you'll drive out the water and make it a powder again. If you cure something under water, it can technically continue to cure for a very long time. Normally you keep it moist for 24-48 hours, and standard testing is done at 28 days. That will get you something like 90% of the final strength, if it can continue to cure indefinitely. I've tested concrete that was semi-submerged for 40 years where the design strength was 4ksi, and it tested out at 14ksi.

RP_Joe 10y ago

China has Fiberglass REbar : https://www.alibaba.com/showroom/fiberglass-reinforcing-bar.html https://www.alibaba.com/showroom/fiberglass-reinforcing-bar....

lisivka 10y ago
Fiberglass does not bend like steel. It will crack instead, which may lead to catastrophic result.

jhallenworld 10y ago

I'm interested in the long term durability of pre-stressed concrete- in its case the reinforcement is critical.

fpaboim 10y ago

I'm a civil engineer. This is bullshit. Reinforced concrete uses much less concrete because, well, you have rebar to take care of tensile stresses and concrete does well with compression so it's much more efficient, which is basic. Also, and a very important point, reinforced concrete (in general) tends to fail in non-catastrophic ways making it safer to use and easier to spot conceptual errors in the project and building process. Reinforced concrete can also be recycled, the concrete becomes structural blocks (I even worked with these before) and the rebar is steel so thats easily recycleable too. In the end, it's cheap and affordable so you can build much more with reinforced concrete than with concrete reinforced with carbon fiber which would last forever but would cost a fortune (this can also be used to reinforce reinforced concrete...) making housing unaffordable to a large part of the world. Do you also really want to spend that much more to make a project to last 500 years without using reinforced concrete? You know that goes into the equation when engineers project strucures right? Oh well, clickbait.

guard-of-terra 10y ago
Just moved into an apartment that's 116 years old. I'm just so happy that people had different perspective back then. It's sad that we don't understand - unsustainable growth, scaffolding and prototyping phase is long overdue.
- learc83 10y ago
  People didn't have a different perspective back then. It's just survivorship bias. People built plenty of crappy disposable buildings 116 years ago, you just don't see them because they were crappy disposable buildings built 116 years ago.
- madengr 10y ago
  My house, currently not there but still own it, is 173 years old. Though that's common in eastern US.
  - ghaff 10y ago
    Mine is just under 200 years old--also in the eastern US. It would be pretty silly though to view my house as this incredible structure that a farmer built 200 years ago to last for the ages. The fieldstone foundation is original as are various posts and beams. But the house has been expanded, rebuilt, updated, etc. in all manner of ways since it was built.

3pt14159 10y ago

I used to be structural engineer, and while things may have changed in the past 8 years since I left, I doubt it. The problem with structural engineering is incentives. It is one of the reasons that I left. Most structural engineering companies are filled with conservative, boring engineers that prefer to look up pre-designed segments and don't make full use of the steel design handbook or building codes. For example, in Canada if you have a non-load bearing brick outer face (most brick buildings in Canada) you're allowed to reduce the wind load by 10%. I was the only person I knew that knew this because I actually read the steel, concrete, and wood design handbooks front to back while I made notes. Furthermore almost nobody has read the building code "just because" they might hop to a section here or there when they need it, but they're generally not going to just sit down and read the thing. So when I would design buildings I would be able to take advantage of a lot more things than most people. This lead to my buildings being cheaper / easier to build, which of course lead to our engineering fees looking like a larger portion of the job. The problem with reinforced concrete is the same. Engineers have no financial incentive to make alterations to their designs to make the buildings last longer. It is almost trivial to make sure steel wont rust (or to double or triple a buildings life) but it makes construction costs go up 0.01% and makes engineerings fees go up 0.1% so nobody does it. Regulators are to blame too. There are amazing concretes (Ultra High Performance Concretes) we should be using in our buildings that completely lack even needing steel because they are so ductile and strong (MPa 200 for the one I was familiar with, Ductal by Lafarge), but it's impossible to use in construction in Canada because the code is so rigid.

colanderman 10y ago
> Most structural engineering companies are filled with conservative, boring engineers that prefer to look up pre-designed segments and don't make full use of the steel design handbook or building codes. I dare say the same is true of software engineering. I, nominally a backend engineer, know (and apply) more about HTTP than most front-end devs and architects I've met, simply because I sat down one day and read the HTTP spec. (It's not a difficult read!)
- sitkack 10y ago

Eric_WVGG 10y ago

This reminded me of a bit from 2014 where some researchers claim to have rediscovered the Roman's particular recipe for long-lasting concrete. http://www.pnas.org/content/111/52/18484.abstract http://www.pnas.org/content/111/52/18484.abstract For laypersons http://www.dailymail.co.uk/sciencetech/article-2877547/Why-Colosseum-hasn-t-collapsed-Roman-concrete-used-secret-ingredient-stand-test-time-engineers-want-copy-it.html http://www.dailymail.co.uk/sciencetech/article-2877547/Why-C...

guard-of-terra 10y ago

Where I live there's a huge number of apartment blocks, most of them built in 60s and onwards, and the apartments are the sole place to live and the prime asset for most people. They'll definitely start crumbling in a few decades and not many people will be able to afford a new home as well as deprecation of their main asset. Have no idea how this might ever resolve, frankly.

Spooky23 10y ago
NYC will have fun times with this problem. They have thousands of mid rise public housing projects built from 1945-1975.
- guard-of-terra 10y ago
  In NYC at least most apartments aren't owned by tenants (are they?). So it'll be landlords' problems.

Lagged2Death 10y ago

The depressing counterpoint, I suppose, is that 99% of the time, you're not building the Pantheon, you're building something that was intended to be minimally-acceptable, utilitarian, and disposable from the get-go: a parking garage, a tilt-up big-box building, a freeway on-ramp, a strip mall. All of which may well be obsolete in a few decades just because the urban environment changes rapidly. If you could figure out a systematic way to cut the cost and the lifetime of such lowbrow, mass-produced concrete structures in half, developers wouldn't hesitate, they'd jump on it immediately. We revere longevity only in retrospect.

keithpeter 10y ago
Most of the big-box buildings I've seen in UK recently are steel frame/breeze block/metal cladding structures on a poured concrete base. The idea being you can basically unbolt the walls when you want to take it down.
fsloth 10y ago
I don't see expendability necessarily as a downside - if the system would support lifetime learning of experts. Building and rebuilding the same thing again and again should be a good way to learn how to make it as good as it can be from design and construction point of view. The problem is if the system does not cherish and support this opportunity to learning and mastery - which many for-profit commercial establishments sadly don't.

bane 10y ago

This article makes an interesting comparison to ancient Roman concrete. While the Romans built a tremendous amount of infrastructure in concrete, survivorship bias means that the few bits that have hung around are seen as some sort of superior quality to Roman understanding of concrete. However, if you go to Rome, most of the surviving bits are millions upon millions of stacked and mortared bricks, and most of what has survived are uninteresting walls. [1] For some reason, our collective memory of Roman ruins is that they're all aged concrete or stone. But when in Rome, you end up seeing lots of this [2], which when built probably had a layer of facade material on it. And it makes sense, stacked, weather resistant, often covered in a prettier facade, baked bricks should last more or less forever until the elements wear them down. The widespread reintroduction of concrete as a building material really didn't happen until around the turn of the 20th century. And reinforced concrete didn't find widespread use until a few decades after that. Not particularly confusing, the first generations of buildings built with these fairly new and only partially understood materials are the buildings that the author is mostly writing about. The real culmination of exposed, reinforced-concrete-everywhere, finally happened in the 50s with the advent of the eye cancer called brutalism. Today a tremendous number of brutalist buildings today are absolutely falling apart, and I blame that on a lack of understanding of how reinforced concrete should be used and the availability of more modern materials and perhaps an overenthusiasm and misuse of materials where they shouldn't have been. But still, if we fast forward a thousand years, there's bound to be a percentage of those structures still around and survivorship bias in the future will lead some to speculate that the engineers of the 20th century were geniuses unrivaled by any in the future. 1 - http://previews.123rf.com/images/13th/13th0902/13th090200009/4338560-damaged-brick-walls-in-the-ancient-Roman-city-Pompeii--Stock-Photo.jpg http://previews.123rf.com/images/13th/13th0902/13th090200009... 2 - http://farm6.staticflickr.com/5185/5762585618_10a11f5a38_z.jpg http://farm6.staticflickr.com/5185/5762585618_10a11f5a38_z.j...

Retric 10y ago
More realisticly zero steel reinforced concrete structures will survive, but other types of buildings might. The house I grew up in for example is pushing 300 years old. That's still a long way to go, but the older it gets the more likely it is to be preserved. A 90% chance it survives any given 50 years = 2-3% chance it makes 1900.

wilsonfiifi 10y ago

I haven't been a practicing engineer since 2007 but if my memory serves me well, to avoid problems of corrosion one often used method was to increase the cover [0](distance from concrete surface to top of steel reinforcement using spacers). I can't see it mentioned anywhere in the article, will probably have to re read it... [0] http://www.buildinghow.com/en-us/Products/Books/Volume-A/The-construction/Reinforcement-Specifications/Concrete-cover http://www.buildinghow.com/en-us/Products/Books/Volume-A/The...

schiffern 10y ago
As both the partial pressure of CO2 in the air and the concrete temperature rises due to climate change, the depth of carbonatation (the process that lowers pH and initiates rebar corrosion) is expected to increase by 45% by 2100 under the A1FI "business as usual" emission scenario. So expect to hear more about this problem in the future. http://www.cipremier.com/e107_files/downloads/Papers/100/37/100037012.pdf http://www.cipremier.com/e107_files/downloads/Papers/100/37/...

nusq 10y ago

This article is full of FUD. What is the alternative? All these reinforced concrete problems are well understood and studied. if proper construction and design codes and maintenance guidelines are followed these structures can last a very long time. In europe we have EuroCodes that account for this problems and to my knowledge concrete cancer is not related with steel corrosion but with a long term chemical reaction between some aggregates and cement. Remember that concrete is cement with sand and stones and the hardning chemical reactions are complex and can last for decades.

schiffern 10y ago
>to my knowledge concrete cancer is not related with steel corrosion but with a long term chemical reaction between some aggregates and cement. It's called carbonatation, it reduces the concrete's pH which leads to rebar failure, and it's only going to get worse with climate change. https://en.wikipedia.org/wiki/Carbonatation https://en.wikipedia.org/wiki/Carbonatation
- nusq 10y ago
  I was refering to alkali-silica reactions https://en.wikipedia.org/wiki/Alkali%E2%80%93silica_reaction?wprov=sfla1 https://en.wikipedia.org/wiki/Alkali%E2%80%93silica_reaction...
  - schiffern 10y ago
    Thanks, TIL!

schiffern 10y ago

Surprised they didn't mention carbonatation and climate chance. tl;dr rising partial pressure of CO2 in the air leads to a spontaneous "reverse calcination" process, lowering the pH which leads to rebar failure. By 2050 most reinforced concrete buildings will be effected. https://www.bostonglobe.com/ideas/2014/10/11/for-concrete-climate-change-may-mean-shorter-lifespan/rJ8vWjSp2xRShwFmDS6lQJ/story.html https://www.bostonglobe.com/ideas/2014/10/11/for-concrete-cl... https://en.wikipedia.org/wiki/Carbonatation https://en.wikipedia.org/wiki/Carbonatation http://ec.europa.eu/environment/integration/research/newsalert/pdf/246na2_en.pdf http://ec.europa.eu/environment/integration/research/newsale...

ChrisNorstrom 10y ago

Didn't epoxy coated steel rebar solve the problem of rust and "concrete cancer" https://www.youtube.com/watch?v=QWUpMWJtgvc https://www.youtube.com/watch?v=QWUpMWJtgvc It's pretty much the standard now.

jorblumesea 10y ago

The real question is do we want buildings to survive 200 years? In 200 years building technology might have advanced far enough that everything is carbon fiber concrete or something far superior. People look at degradation of a structure as some kind of serious issue, but it can also be seen as a positive.

syphilis2 10y ago
To expand on this, will our descendants have the same demands in 200 years? Will a revolution in transportation dramatically change infrastructure needs? What will employment look like, how will businesses operate? Will citizens want the structures we build in the locations we build them? The author suggests we build structures to stand the test of time and addresses structural, economic, and environmental needs, but not societal ones. The Moai referenced are not artifacts because they weren't engineered well enough, they're artifacts because they outlived the societies that built them.

foxhop 10y ago

Research "rammed earth" and "earth ships" for details on why old structures last longer. Rammed earth has great thermal mass which has huge benifits if controlled.

etatoby 10y ago

I see a lot of engineers calling the article FUD and BS, what with it mentioning ancient Roman buildings and mud bricks. I also see several commenters (myself included) wholeheartedly agreeing with the point it makes. I think bluthru hit the nail on the head somewhere below (which will soon be above?) > The point is that longer-lasting structures should be cheaper, but because we don't factor in environmental harm and lifecycle cost into the price of things we end up with cheap buildings that exist to generate ROI ASAP. Factoring in those kinds of costs runs contrary to mainstream economic doctrine, so the question really is whether you think that capitalism (in its current form) is doing more harm than good for our communities and/or for our species as a whole, especially including future generations. Do you?

ams6110 10y ago
Cheap building to generate ROI ASAP sounds a lot like MVP to me. And MVP is what everyone here advises.

combatentropy 10y ago

I like the look of brick. It lasts a long time too. Why don't we use it more?

Spooky23 10y ago
High labor costs. Also the postwar construction boom dominated by big projects killed the industry for higher end brick.
- TheCowboy 10y ago
  The high labor costs also resulted in brick masonry becoming a basically lost art. There was a building a few blocks away from where I used to live, where a car crash had led to a catastrophic collapse of a circular structural brick tower. It was an eye sore for years and years. The owners apparently couldn't find the skills to repair it for a long. The repair looks great but doesn't perfectly match. Even with the hassle, structural brick buildings are great.
colin_mccabe 10y ago
At least in California, we don't use it because brick buildings crumble in earthquakes. http://www.latimes.com/local/lanow/la-me-ln-quake-safety-thousands-of-brick-buildings-still-not-retrofitted-20140826-story.html http://www.latimes.com/local/lanow/la-me-ln-quake-safety-tho... In new construction, you can use it as a facade, but not for anything structural (to oversimplify a bit.) Elsewhere in the US, brick would probably be a good choice, but it's more expensive than slapping together another bargain-basement wood-frame house. On the other hand, for some reason, Europe has a lot of brick buildings and even still puts in brick streets sometimes.