
How Ancient Rome’s Concrete Has Survived 2,000 Years (2017) - diodorus
https://time.com/4846153/ancient-rome-concrete-cement-seawater/
======
dang
Related from 2017:
[https://news.ycombinator.com/item?id=14690329](https://news.ycombinator.com/item?id=14690329)

2013:
[https://news.ycombinator.com/item?id=5883443](https://news.ycombinator.com/item?id=5883443)

~~~
Aloha
I really appreciate the good you do for the HN community.

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DenisM
In an earlier thread someone working in the industry said that today the
cement producers can make arbitrarily sturdy concrete, but almost no one wants
to pay for the top-tier stuff.

Part of it nearsighted thinking, the other part is consideration that money
could be spent on like nicer decor, or maybe build larger number of 100 year
buildings than a smaller number of 1000 year buildings.

~~~
merpnderp
Isn’t it the height of hubris to believe we could plan 100 years ahead? What
cities haven’t radically changed in the last 100 years, with nearly everything
being replaced with something better than they could have conceived of?

~~~
ethelward
> What cities haven’t radically changed in the last 100 years, with nearly
> everything being replaced with something better than they could have
> conceived of?

95% of European cities downtown?

~~~
paganel
You’d be surprised. Almost all of the German cities were destroyed in WW2
(meaning their downtown area). The same goes for Polish cities, or further
East cities like Kiev, Odessa or Kharkiv. WW2 was also quite brutal for
Western cities like Rotterdam or London. WW1 obliterated most of the cities in
Northern France and South-West Belgium. The streets of Madrid saw active and
intense fighting in the Spanish Civil War. And many of the cities that escaped
the wars relatively unscathed had to contend with the modernist movement of
the 1960s and the 1970s, which saw many interesting buildings demolished
because they didn’t look modern or functional enough (Athens being a prime
example for this).

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nullstyle
For all of your internet-based concrete knowledge needs, I highly recommend
Tyler Ley, a professor from Oklahoma State:
[https://www.youtube.com/watch?v=PMed3YtN-
Fo](https://www.youtube.com/watch?v=PMed3YtN-Fo)

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peterwwillis
There's another ancient building technique that doesn't get considered in the
modern era: cutting and moving gigantic 10-ton blocks of stone. Sure, it's
expensive to cut and move, but a bunch of dudes with rickety boats did it
across huge expanses of land and water, and their structures also still stand
today.

If the carbon footprint is a concern, it might be a perfect opportunity to
propose alternatives to the carbon-intense techniques we've adopted. For
example, William Fairbairn invented a _hand-powered_ crane, whose 642-to-1
ratio meant two men turning cranks could lift 60 tons. Our land and water-born
vessels could also probably be innovated on with similar efficiency, if it
wasn't so damn easy to burn ancient vegetation.

~~~
quakeguy
If time isn't an issue, those techniques all are fine and are proven to work.
Sadly, time IS an issue today, so 2 men on a paddle won't build the hoover
dam. Even if they could.

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jblow
Are you claiming that construction today is fast? I don’t understand.

Are you claiming that a contemporary construction project would be able to
build the Hoover Dam? That was almost 100 years ago and a lot of things have
changed...

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cjohansson
Funny that discovering how they did concrete 2000 years ago can be seen as
progress..

~~~
thrwaway3948
that is a little funny you're right. It reminds me of something interesting I
read, don't know if it's true or not. I heard that in the "middle ages" (or
dark ages) it was taken for granted that the ancients -- meaning the Greeks
and maybe even the Romans, not sure -- had been way wiser and more
knowledgeable than them. (You know, as they read Euclid's elements and
Socrates and stuff.) As I remember it, all the way through the Renaissance
that was the thinking, that the ancients had known way more.

Imagine thinking that the ancients knew more than we ever will, and trying to
study their works to get at just some of the wisdom they had held. I think few
if any people read ancient authors that way today.

however my memory on this subject may be shaky.

~~~
jbverschoor
There was this excellent video about the misconception that technology and
knowledge advances over time.

It does not. It fades, gets lost. Where are the Steve Wozniaks and bill gates?
Where are the people truely understanding this stuff. Where are the people who
can optimize code like back in the days?

~~~
michaelvoz
I think you are conflating the notion that, at a given time slice, a majority
of the popular sentiment about the future may not have always been positive,
with your own opinions of modern engineering.

For vast swaths of human mind, popular opinion tended to see the future as
bleak and the past as filled with greater men, accomplishments, etc - the good
days are behind us. Post industrial revolution thinking and adoption of
science has mostly changed that opinion to hope - the good days are ahead of
us.

As for people who can optimize code like back in the day: I am not sure where
you work, but I bet if you look at the best engineers in the best tech
companies today (google/ Facebook / Netflix / amazon / Uber / palantir) you’ll
find a lot to be impressed with.

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kazinator
How ancient Rome's concrete has survived that long can probably be attributed
to one main factor: no inclusion of steel rebar.

~~~
aswanson
Raises an interesting question: how long can modern bridges last, given they
consist mostly of steel?

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jacobush
The worst is when you combine materials who age differently or respond to
temperature swings differently.

If that steel bridge can be kept from rusting, it can keep a long time.

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petre
Also steel has an endurance limit where material fatigue plateaus.

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sokoloff
What’s way stranger to me is that aluminum does not have an endurance limit
(for non-Mech E’s, this is worse for aluminum even though it sounds like it
might be better).

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namibj
Basically, there is no deformation so miniscule that it lasts forever. It just
affects how many cycles/how long it takes. Steel however, if you deform it
only very little, lasts practically forever. You just need to design it to not
deform too much at normal operation.

Incidentally, this fatigue vs. approaching the strength limit issue is why
airplanes have limited flights. The fuselage/hull is made to last long enough,
but not necessarily do well longer than that.

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tictok4
Meanwhile the 20 year old office building I work just had extensive repairs to
the concrete.

~~~
duxup
Survivor bias, we only get to see Roman successes today ;)

~~~
jbay808
You're probably joking, but since "it's just survivor bias" is a popular take
these days, I'll respond as though you're serious.

A bridge that stands for 2000 years without (much) maintenance isn't survivor
bias, it's disruptive technology.

Yes, we only see the best of Roman architecture, and most Romans probably
lived in wooden shacks or stone apartments that have long since crumbled or
been demolished.

But Roman concrete is chemically different than the Portland cement that was
invented in the 1800s, and although there's certainly a distribution of
building quality and workmanship that will result in a wide spread of
lifetimes, we don't have any reason to expect that any concrete building built
from Portland cement and exposed to the elements like Roman seawalls were will
last 2,000 years. The distribution just doesn't have that long of a tail to
it.

~~~
joshspankit
An important component to the survivor bias argument in this case is: we have
no way of knowing what roman concrete _didn’t_ survive. Maybe the ones
standing are atypical, or were in some way a fluke as opposed to the marvel
they seem to be.

~~~
jbay808
Sure, but that's also not really the point.

When we see these structures standing, our reaction should be "wow! How did
they do that? What can we learn?"

Not "well, I bet they also built a lot of bad buildings too; nothing to see
here".

When you build something twice as good as the average, it's a fluke. When you
build something 20x as good as average, it's worthy of study. Even if these
are atypically good examples of Roman architecture[1], you can't pull off the
moon landings by launching a ton of backyard fireworks and hoping for a long-
tailed success distribution.

The best buildings represent the state of the art of the best architects and
the best masons working with access to quality materials and an adequate
budget and timeline. Not dumb luck and guesswork paying off.

[1] Which there are decent reasons to not expect. For example, we know that
many Roman buildings were demolished deliberately by later generations because
they weren't Christian enough, rather than because they collapsed.

~~~
shultays
Sure, surviving for such a long time is a big accomplishment but compared to
bridges today, they are relatively short bridges that cost more to build and
allows less load. What is there to research other than figuring out how they
work? They are well structured blocks of rocks that distributes the load well
basically.

How they were built is probably more interesting, but still would be useless

~~~
jbay808
As the article explains, the most interesting thing is their seaworthy cement.
Although today's Portland cement is newer, it wasn't adopted because it was
superior to Roman cement, but because (until recently?) no living person knew
how to make Roman cement.

Hence, we can indeed learn something by studying it.

~~~
darkerside
It's typically not the case that we can't make things as well as we use to.
It's just that we've found ways to make them that are cheaper by an order of
magnitude and last just long enough to do their job.

Roman concrete wasn't disruptive. It was disrupted.

~~~
jbay808
> Roman concrete wasn't disruptive. It was disrupted.

I'm amazed by this mentality. It's like the very possibly of a technology
being forgotten, rather than surpassed, is axiomatically impossible.

If "everyone who knew the recipe died" counts as getting disrupted, then yes,
it was disrupted. And if Roman concrete counts as more expensive because the
supply is literally zero, the yes, modern concrete can be seen as cheaper.

But understand that modern Portland cement wasn't invented to improve on Roman
concrete, but rather as an attempt to replicate it, because nobody until then
had any guess.

~~~
darkerside
That's not my mentality at all. I understand technology can be lost and
forgotten.

In this case, I actually think the naive mindset is the one that assumes, more
durable is better. No, more durable is more durable. Is static typing "better"
than dynamic typing? No, it's a different tool for a different task.

Please don't fall for clickbait. It sounds so cool to have lost a technology
over time, and it certainly is possible, but I don't think that's what
happened here.

Here's a quick Google source. Sorry for PDF.
[https://www.google.com/url?sa=t&source=web&rct=j&url=https:/...](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ascconline.org/Portals/0/Technical-
Article-
Aug-2017_WebSC.pdf%3Fver%3D2017-08-16-144954-857&ved=2ahUKEwjPmP3frcfjAhWkKqYKHQuEDGEQFjANegQIARAB&usg=AOvVaw1b6yy2D_RKlPg8nTAR-9-n)

~~~
jbay808
Hmm, a few points...

1) This certainly doesn't imply that Roman concrete was discarded because a
more cost effective formula came along. The fact is that it was lost to
civilization for over a thousand years, and then Portland cement was
discovered. There was no period of time in which a contractor could choose one
or the other and selected Portland cement for price or performance reasons. So
beyond a doubt the Roman technology was lost.

2) That article is pretty unconvincing, being basically just a blog post by a
cement guy who points out the same things that anyone else should already
expect, all of which were mentioned in the comments section here. And not only
because the author misspelled Raman spectroscopy.

3) Survivor bias has been addressed in several other comments. It's a valid
point if someone points to a 2,000 year old bridge and says "my building
needed repairs after just 10 years; clearly no Roman buildings ever had that
problem". Yes, I'm sure the Romans also built buildings that fell apart within
10 years and needed repairs. Those bridges don't say anything about the
quality floor. But that's really missing the point.

The quality ceiling is also not an accident which is my point about the moon
landings. Most rockets launched in the 20th century were backyard fireworks,
so you could point to the moon landings as "survivorship bias that doesn't
reflect the crude state of 20th century rocketry in which most rockets were
just backyard fireworks and few even made it to space, we just only remember
the ones that did".

But that statement, while true, also makes it sound like the moon landings
were a statistical fluke in which a bunch of people who had no idea what they
were doing got lucky and lauched some fireworks that made it to the moon. That
would just be wrong. Likewise the best Roman buildings were not built by luck,
but by skilled engineers with large budgets, and they are just as impressive
as they seem. It's no coincidence that the structures that survive are high
budget state infrastructure projects, government and religious buildings, and
estates of exquisite craftsmanship, and not random commoners' houses, even
though there were probably 10,000 houses for every aqueduct.

Survivorship bias also doesn't mean there's nothing to learn from those
materials. Probably not every batch of Roman concrete was perfectly formulated
to perform optimally, but that's no reason not to study the surviving samples
and note their impressive durability.

Randomness isn't everywhere. If you dump a thousand ball bearings in the ocean
and pull them up ten years later, you expect to see a thousand rusty ball
bearings. If one of them is somehow still smooth and polished, you don't
conclude that erosion just acts randomly and it's survivor bias. Instead, you
should look closer and see if maybe that one was actually made of 316
stainless or something.

------
blacksqr
The Last Centurion of civil engineering.

------
867-5309
[https://youtu.be/3o-r1-AsmRU](https://youtu.be/3o-r1-AsmRU)

