

Volcanic sand has been credited with the longevity of Rome’s ancient monuments - danielharan
http://www.washingtonpost.com/news/morning-mix/wp/2014/12/16/the-secret-ingredient-behind-romes-lasting-monuments/

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hvs
A big part of why Rome's monuments have lasted is they didn't use reinforced
concrete. Reinforcing with steel rebar allows much thinner concrete walls than
without, however it also makes them susceptible to rust/expansion/crumbling
when water gets into the material.

~~~
therealdrag0
Any idea when/where this changed and reinforcing was used?

~~~
jacobolus
[https://en.wikipedia.org/wiki/Reinforced_concrete#History](https://en.wikipedia.org/wiki/Reinforced_concrete#History)

 _François Coignet was a French industrialist of the nineteenth century, a
pioneer in the development of structural, prefabricated and reinforced
concrete. Coignet was the first to use iron-reinforced concrete as a technique
for constructing building structures. In 1853 Coignet built the first iron
reinforced concrete structure, a four story house at 72 rue Charles Michels in
the suburbs of Paris. Coignet 's descriptions of reinforcing concrete suggests
that he did not do it for means of adding strength to the concrete but for
keeping walls in monolithic construction from overturning._ [...]

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RRWagner
Joseph Davidovits explains the chemistry behind this and much more in his
books and other works over many decades. Once ridiculed, acceptance of his
ideas has slowly grown. Certainly the chemistry that he describes is very
repeatable, and the Pantheon and other Roman works are very … can't resist …
concrete examples and proof of his ideas. Follow the links in this wiki
article and do some Google searches. I read the book in 2000, and was very
impressed by the time I finished it. I later met with Davidovitz, and found
him to be quite reasonable, intelligent and clear thinking. The biggest
obstacle was/is that it was in more people's interest to promote the "mystery
of the pyramids", and established dogma in academic circles than to just
repeat his experiments.
[http://en.wikipedia.org/wiki/Joseph_Davidovits](http://en.wikipedia.org/wiki/Joseph_Davidovits)

~~~
dalke
The WP link includes a link to (after correcting the location) the paper at
[http://nebula.wsimg.com/624fc4188a1d8eb2d1ad010ca81ef8c1?Acc...](http://nebula.wsimg.com/624fc4188a1d8eb2d1ad010ca81ef8c1?AccessKeyId=D94D99729EAEC69E9267&disposition=0&alloworigin=1)
which says:

> This study conclusively demonstrates that there is absolutely no evidence of
> an alkali-aluminosilicate-based composition in the binder phases of the
> casing stones, nor is there any evidence of “unusual” constituents in the
> pristine, bulk uncontaminated interior of the casing stones to call for a
> “man-made” origin. Despite the detection of a man-made “coating” on the
> Lauer casing stone, the stone itself is determined to be nothing but a high-
> quality natural limestone mineralogically, texturally, and microstructurally
> similar to that found in the quarries at Tura-Masara. ...

> Despite its many reported ancient routes, and unquestionable potential
> future applications of geopolymer technology, the Egyptian pyramids, in
> author’s opinion, still stand as marvels and mysteries of ancient
> engineering technologies exercised by the Old Kingdom (2500 BC) stone
> masons.

As a non-geochemist, I can say nothing about it one way or the other, and I
know that I can be easily swayed by good sounding but wrong statements.

Perhaps it's like Thor Heyerdahl's Kon-Tiki. He showed that it was possible to
go by balsa wood raft to Polynesia. That doesn't mean his diffusionist model
of cultural development was what happened. That the Egyptians could have used
geopolymer technology doesn't mean they did.

------
Isamu
I recommend Diana Kleiner's awesome course on Roman Architecture
([https://www.coursera.org/course/romanarchitecture](https://www.coursera.org/course/romanarchitecture)
and [http://oyc.yale.edu/history-art/hsar-252](http://oyc.yale.edu/history-
art/hsar-252)). It was eye-opening to me just how much they relied on
concrete.

Roman concrete was called opus caementicium. The Romans had two main sources
of the right kind of volcanic ash in Italy, the main one in Pozzuoli
([http://en.wikipedia.org/wiki/Pozzolan](http://en.wikipedia.org/wiki/Pozzolan))
but apparently they mined other places, such as in Eifel where it is known as
Trass
([http://en.wikipedia.org/wiki/Trass](http://en.wikipedia.org/wiki/Trass)).
For example concrete was used in the very extensive aquaducts serving the
Roman city that is now Cologne.

It is very similar to lime plaster (lime and sand) and so it is thought to
have been discovered by simple substitution of local pozzolan for sand.

The advantage of Portland cement is that it cures very quickly. Roman cement
takes something like a month to cure.

Another apparent advantage of Roman concrete is that they were able to throw
up large structures with concrete vaults or domes with a large workforce in
relatively short time frames, whereas the Medieval cathedrals (which were
based initially on the same Roman basilica) took a smaller, highly skilled
workforce long periods to cleverly piece together without concrete.

Pozzolan is used today, generally as an additive. Note that fly ash is similar
([http://www.ctlgroup.com/lab-services/lab-
tests/astm-c-618-co...](http://www.ctlgroup.com/lab-services/lab-
tests/astm-c-618-coal-fly-ash-raw-calcined-natural-pozzolan-use-mineral-
admixture-concrete/)). Again because of the long cure time the original Roman
concrete is not in favor, but you may achieve the performance you need through
the use of an admixture.

I should add that some of these recent articles may be linked to the general
business interest in the increased use of pozzolanic admixtures, since there
is a ready source in fly ash and also some parts of the world have vast
amounts of pozzolanic ash ready to be exploited.

~~~
julespitt
I second the recommendation of Diana Kleiner's video lectures. Absolutely
fantastic, thorough, and well explained.

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ams6110
Both recipies call for heating the limestone. So why is the modern process so
much more energy-demanding? Is it heated to higher temperatures?

~~~
julespitt
Yes, and there's more - Portland cement is made of constituent parts, each
presumably extracted from different stones (using energy intensive processes)
and then precisely recombined in certain ratios. Roman concrete, lime mortar,
and Natural cement are made largely from just moderately heating limestone.

------
vaadu
What volcano produces the best ash? Can it be man made? Strip mining for ash
around volcanoes doesn't sound environmentally friendly.

------
huxley
I quite enjoyed Professor Stephen Ressler's video course series "Understanding
Greek and Roman Technology: From Catapult to the Pantheon"

[http://www.thegreatcourses.com/courses/understanding-
greek-a...](http://www.thegreatcourses.com/courses/understanding-greek-and-
roman-technology-from-catapult-to-the-pantheon.html)

If you enjoy history of architecture/engineering, it's worth picking up when
it's on sale, the video quality is standard def, but you can either stream the
videos or download DRM free copies of each lecture.

------
WalterBright
Roman concrete has been known about for a long time. Why doesn't anyone use
it?

~~~
wiredfool
(Note, not a CE any more, but I did Civil Engineering @ Cornell with
Professors that were big into concrete, where many of the people who wrote the
paper are from.)

First of all, I bet that the strength of the concrete builds pretty slowly.
They're mentioning a 180 day test, where most modern concrete is considered
'fully cured' at 28 days, and generally you're looking at a few days to a week
before it's got enough strength to continue construction. (Note that concrete
will continue to cure indefinitely as long as it's kept moist and at a good
temperature. E.g., I looked at some concrete from a floating bridge that was
40 years old and it was 3x stronger than it was supposed to be based on the
original specs. There's some scatter in those, but 40 years in a cool poist
environment didn't hurt.) Also note that there are a lot of interesting
additives to concrete that can change the behaviour of modern concrete, to
make it easier to place, faster to set, slower to set, pumpable, high
strength, high stiffness, or whatever.

Second, Concrete tends to be a pretty local thing. You don't tend to ship the
raw materials long distances, since they're heavy and low value. In places
where there is volcanic ash, it can be used. But then you get to places like
the whole US east of the Rockies, and there's none of that.

Third, we lost the recipe for Roman Cement for the better part of 2 millennia,
and only recently rediscovered it, well after the discovery of Portland Cement
and it's spread through the world.

~~~
saalweachter
Case in point, Rosendale cement[1] is another natural cement. It was popular
in the 19th century because it does not require additives to produce (the
limestone already contains the desirable traces) and can set underwater. Being
produced along the Hudson River, one of the biggest shipping routes of the
day, probably didn't hurt. However, it requires significantly longer to set
and was discarded in favor of the faster setting Portland cement.

[1]
[http://en.wikipedia.org/wiki/Rosendale_cement](http://en.wikipedia.org/wiki/Rosendale_cement)

(Bonus factoid: while Rosendale cement is named or the location of the
limestone deposits mined to produce it, Portland cement is named for the
resemblance of the finished product to Portland stone,
[http://en.wikipedia.org/wiki/Portland_stone](http://en.wikipedia.org/wiki/Portland_stone))

------
lazyjones
Longevity of modern building techniques (or rather lack thereof) is a pet
peeve of mine. Romans, Greeks, like many other ancient cultures built for
millennia with much simpler means than we have available today, while the
methods a building contractor is offered these days yield lifespans of 30-100
years maximum (that's in Europe where we don't typically build something that
needs only last till the next Hurricane). It's a sad state of affairs, owed to
the throwaway mentality we have about pretty much everything today.

Those who find Roman concrete interesting, might want to look into various
forms of artificial stone too (used in the 19th century):
[https://en.wikipedia.org/wiki/Artificial_stone](https://en.wikipedia.org/wiki/Artificial_stone)

~~~
chongli
Modern builders are operating on a much different set of constraints than the
Romans. Simply include 2 additional factors in the equation (cost and harsh
climate) and the Romans would not have fared nearly as well. The circumstances
under which all of these ancient structures were built were more-or-less ideal
for longevity. Is this a coincidence? No, it's survivorship bias[0].

    
    
        [0] https://en.wikipedia.org/wiki/Survivorship_bias

~~~
lazyjones
How is the climate worse nowdays than in the past 2000 years? For a sensible
comparison, look at the (many) wars these buildings had to endure as well.
It's easy to claim survivor bias, but the durability of these buildings is
simply a matter of technical analysis and specification, as with modern
construction. I had to choose the material for a building facade (renovation)
recently and the best option for longevity was: natural stone, the worst being
the most commonly used type.

~~~
chongli
When I mention survivorship bias, I do so in order to highlight that people
are being selective when talking about _those buildings which have survived_
and ignoring the vast multitudes of Roman and other buildings which have not.

As for climate? Yes, the climate where I live (Ontario, Canada) is vastly more
harsh than Rome (ancient or modern). Why do I bring this up? Because generally
the people making these sorts of survivorship biased observations are also
neglecting to control for other significant variables such as location.

You also didn't mention cost. Many of the great Roman structures which have
survived to this day would have astronomical costs should we attempt to build
them in the modern day using ancient building techniques and materials.

~~~
lazyjones
> _You also didn 't mention cost. Many of the great Roman structures which
> have survived to this day would have astronomical costs should we attempt to
> build them in the modern day using ancient building techniques and
> materials._

I'm not so convinced as far as materials are concerned. Techniques have
improved and modern ones could be used (cranes etc.). The main issue I see
here is that materials aren't even available anymore, nor are they legal
w.r.t. building codes. So even if cost wasn't a factor, I don't see how anyone
could build a modern building with Roman concrete, marble etc.

~~~
ajuc
Ban on slavery really drives costs up :)

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Htsthbjig
Secret?

How is that secret?

Pozzolonic mortar ingredients have been know for a long time.

In fact, ashes have been used for making concrete for a long time too
nowadays. Blast furnaces produce ashes that are routinely used for that.

Bad title. In the article then they say that what is secret is the reason why
pozzolonic mortar withstand well time.

Sensationalist reporting...

~~~
dang
It isn't secret, just the usual linkbait. We changed the title to a
representative sentence from the article.

