
The problem with reinforced concrete - danfru
https://theconversation.com/the-problem-with-reinforced-concrete-56078
======
3pt14159
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
> 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
How many of us actually read the documentation and the source for the systems
we use? All the options and flags for jq, wget, socat, ssh, rsync, etc. I am
trying to spend about 5 minutes a day just reading man pages, esp about things
I THINK I know but actually don't.

~~~
jonaf
In my personal experience, the best engineers I've encountered (and learned
from) have understood every system, subsystem, and interaction, all the way
down to the most fundamental foundational level. And this understanding allows
them to make the best decisions (because they're equipped with the best
information). This knowledge doesn't come by sitting down and studying how CPU
architecture works when you're building a web application. But it _does_ come
from diving as deep as is required for any given task. So maybe if you're
dealing with a web app performance bug and you have to crack open Chrome
source code, trace it down to something that is compute-intensive, learn
whatever C++ code is involved, understand how it utilizes the CPU, and learn
about the specific architecture you're using that exhibits the problem, then
you have ultimately obtained a significant depth and breadth of information,
but at the end of it, you know and _understand_ _exactly_ why your web app
performs the way it does, how to workaround it in your app, how to fix it in
Chrome (or why you shouldn't), and how the CPU architecture affects the Chrome
source code. Now you can apply Chrome, CPU architecture, and C++ to anything
that is built upon any one of them (independently or otherwise). That's not to
say you know _everything_ about each of them, but you've learned things that
will help you in the future in some cases.

The most important skill here is being able to diagnose a problem and
fearlessly, relentlessly employ the engineering discipline of solving whatever
problem/task is at hand, and not because of observed symptoms ("hey, I turned
that knob and everything was OK! I don't know why, but I can close this JIRA
ticket and move on with my life. I'm a 10X engineer!") but because you
understand precisely what's happening. I made the mistake of the first decade
of my software engineering career learning from trial/error and observations,
and while those skills are useful in some cases, the best engineers are
extremely disciplined about understanding the _full_ depth of a problem before
writing a line of code.

In a nutshell, I guess what I'm advocating for is _do not blindly study man
pages._ The reason is because without a practical application for the
knowledge, it seeps out of your brain and you forget it quickly. The exception
(case in point, GP's example) is when what you're studying _does_ have a
practical application or is relevant to what you spend your time doing. This
has always been my problem with academic curricula (sure, some people can
learn well this way, and there's definitely a minimum foundation necessary
that must simply be committed to memory). Even in basic subjects like maths --
the work is rote, and we maybe get a passing grade, but often without the
understanding (or the _depth_ of understanding) that is really the most
important aspect of learning the subject matter.

~~~
kiba
People have time to do that while on the job? To understand something at a
deep level?

~~~
erikpukinskis
I think everyone has time for it, but it requires nerves of steel. You are
thinking "I could just fix this the easy way", you are feeling social pressure
to quickly get to the next thing. It's easy to decide "I can't take the time
to really figure this out."

But if you can ignore the pressure and stick to your guns, you end up saving
time in the long run, sometimes making orders of magnitude more work possible.
Most managers should appreciate that.

But it's difficult to have the nerve to do it, and it can be difficult to
explain in the short term. Like most opportunities there's a cost to pay up
front.

~~~
rhizome
Would that we as a profession developed an encyclopedia of ways of pushing
back on "Is it done yet? How much longer?" completion pressure. There's
certainly a profusion of lore about PFYs and lusers, why not structural
business frustrations?

------
dkbrk
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.

~~~
jessaustin
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.

~~~
gkop
Aren't blocks supposed to be reinforced with rebar and columns poured through?
How easy are they to recycle in practice after this? Just curious.

~~~
HillaryBriss
Yes. I believe that's the code in Los Angeles.

~~~
hga
Yeah, if you're in an earthquake zone, like the Pacific Ring of Fire
([https://en.wikipedia.org/wiki/Ring_of_Fire](https://en.wikipedia.org/wiki/Ring_of_Fire)),
which most certainly includes California and the Philippines, you're
eventually going to be very unhappy if you don't reinforce them.

------
fpaboim
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.

~~~
lisivka
Why not just use straw, instead of carbon fiber, in concrete? Straw is
comparable to steel. Chopped straw is used for stucco, but it can be used in
reinforced concrete too. It is hard to calculate amount of straw, which is
necessary to reinforce concrete, because it strength varies, but it cheap, so
just triple amount of straw.

~~~
guard-of-terra
Straw is biodegradable. It will degrade.

~~~
lisivka
When straw/wood is enclosed in concrete with some lime, it does not rot. I saw
video[1] of remains of houses built by German prisoners in Siberia using "soft
concrete" \- concrete with wood chips (cement bonded particle board, AKA
Arbolite, fiber reinforce concrete, Papercrete, etc.). They are looking good
after about half of century without any maintenance of houses, even in broken
walls without roof.

From my own experience, I saw that wood rots quickly for about 1cm (1/2") when
it contacts with concrete or cement stucco, but remains intact when enclosed
in cement-lime mix. IMHO, lime is important to save wood/straw from rotting.

[1]
[https://www.youtube.com/watch?v=iAiT6IRVgTE](https://www.youtube.com/watch?v=iAiT6IRVgTE)

[2]
[https://en.wikipedia.org/wiki/Papercrete](https://en.wikipedia.org/wiki/Papercrete)

------
bane
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...](http://previews.123rf.com/images/13th/13th0902/13th090200009/4338560-damaged-
brick-walls-in-the-ancient-Roman-city-Pompeii--Stock-Photo.jpg)

2 -
[http://farm6.staticflickr.com/5185/5762585618_10a11f5a38_z.j...](http://farm6.staticflickr.com/5185/5762585618_10a11f5a38_z.jpg)

~~~
godzillabrennus
Roman concrete holds up against the erosive properties of seawater better than
the materials used today. Scientists discovered it's because they used
volcanic ash to make their concrete.

[http://newscenter.lbl.gov/2013/06/04/roman-
concrete/](http://newscenter.lbl.gov/2013/06/04/roman-concrete/)

~~~
schiffern
That's part of it, but mainly roman concrete holds up much better because they
never used reinforcing rebar. Volcanic ash improves longevity further, but if
they had included rebar (volcanic ash or no) all those structures would have
rotted away a long time ago.

------
reidacdc
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
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.

------
etatoby
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
Cheap building to generate ROI ASAP sounds a lot like MVP to me. And MVP is
what everyone here advises.

------
jpt4
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
That basalt rebar is very interesting - what is the cost compared to steel?

~~~
jpt4
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
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...](http://www.tdbazalt.com/category/materiali_dlia_stroitelstva_i_otdelki/armatura_stekloplastikovaya/nedostatki_stekloplastikovoi_armaturi_minusi/)

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)

------
Lagged2Death
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
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.

------
Eric_WVGG
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-C...](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)

------
nusq
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
>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
I was refering to alkali-silica reactions
[https://en.wikipedia.org/wiki/Alkali%E2%80%93silica_reaction...](https://en.wikipedia.org/wiki/Alkali%E2%80%93silica_reaction?wprov=sfla1)

~~~
schiffern
Thanks, TIL!

------
greydius
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
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
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.

------
jorblumesea
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
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.

------
guard-of-terra
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
NYC will have fun times with this problem. They have thousands of mid rise
public housing projects built from 1945-1975.

~~~
guard-of-terra
In NYC at least most apartments aren't owned by tenants (are they?). So it'll
be landlords' problems.

------
schiffern
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-
cl...](https://www.bostonglobe.com/ideas/2014/10/11/for-concrete-climate-
change-may-mean-shorter-lifespan/rJ8vWjSp2xRShwFmDS6lQJ/story.html)

[https://en.wikipedia.org/wiki/Carbonatation](https://en.wikipedia.org/wiki/Carbonatation)

[http://ec.europa.eu/environment/integration/research/newsale...](http://ec.europa.eu/environment/integration/research/newsalert/pdf/246na2_en.pdf)

------
wilsonfiifi
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...](http://www.buildinghow.com/en-
us/Products/Books/Volume-A/The-construction/Reinforcement-
Specifications/Concrete-cover)

~~~
schiffern
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/...](http://www.cipremier.com/e107_files/downloads/Papers/100/37/100037012.pdf)

------
RP_Joe
China has Fiberglass REbar : [https://www.alibaba.com/showroom/fiberglass-
reinforcing-bar....](https://www.alibaba.com/showroom/fiberglass-reinforcing-
bar.html)

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

------
foxhop
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.

------
ChrisNorstrom
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.

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

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

~~~
Spooky23
High labor costs.

Also the postwar construction boom dominated by big projects killed the
industry for higher end brick.

~~~
TheCowboy
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.

