
New studies of ancient concrete could teach us to do as the Romans did - dnetesn
https://phys.org/news/2017-07-ancient-concrete-romans.html
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trextrex
According to the history on wikipedia's page on Tobermorite [1], this has been
known at least since 2013.

[1]
[https://en.wikipedia.org/w/index.php?title=Tobermorite&actio...](https://en.wikipedia.org/w/index.php?title=Tobermorite&action=history)

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omegant
I've been reading lately about the properties of lime mortarand concrete
(check "building with lime"). I have an early 50's garaje that has rammed
earth walls. Because recent covers with portland and plastic paint, the
humidity is destroying the wall from the inside.

Amazingly the solution seems to be more breathable mortar cover using lime in
the traditional way. This goes contrary against all the recomendations from
modern buiding codes.

Lime mortars and concretes are very interesting for not technical (bridges and
skyscrappers) applications. Lime cures absorbing CO2 and "petrifying" for
months. It has much lower compression strength, but that helps to preserve the
stone used to build. When there is thermal or ground movement, the part that
breaks is the lime binder and not the rock, making it easier to repare
(concrete is so strong that it breaks the whole wall). Also for small fisures,
lime is self healing, it disolves with humity and fills the micro cracks. This
way you can see this old european buildings that are actually leaning slightly
in some direction but holding without mayor failures.

Another advantage is that it's breathable when using it as a wall cover. You
don't develope "humity" stains in your wall nor it leaches white salts like
the porland cement.

It can also be used to stabilize a road or ground around a house without
pouring concrete, specially if you have problems with mud. Just mix a small
part of lime for square meter of land, wet and ram. The ground will hold much
better heavy traffic and absorb water when it rains. They are using this
technique in some southamerican jungle roads as it's cheap and holds well.
I've also seen videos of this method being used to improve the ground of
factories.

Painting or sculping with cured lime (lime that has been rehydrated and wet
for months, to allow it to cristalize). Gives you a sanitizing surface because
it's extremely alcaline.

It's not a super material, in fact the structural properties are mediocre
compared to modern ones, but the overall advantages are quite interesting for
small buildings, decoration, and given that you are roman you could buid quite
durable structures.

Very different concepts of how building materials should behave compared with
modern materials (more isolation, more strength and stiffness).

About the rebar, I've read some articles about using basalt rebar (basalt
glass fibers binded with epoxy). They say it's structurally stronger than
steel and not degrading nor corroding. I don't know if it really works.

Edit 1 & 2: typos and formating. Writting from the phone..

~~~
wowtip
Interesting, any reading recommendations books/links for this?

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omegant
Most sources are from restorers of old buildings and lime associations.

Building with Lime: A Practical Introduction by Stafford Holmes et al. Link:
[http://a.co/3BdZ2tp](http://a.co/3BdZ2tp)

There is a book that it's virtually impossible to find: Artes de la cal by
Ignacio Garate Rojas, who was restorer of the Alhambra de Granada and several
other monuments in Spain.

[http://anfacal.org/media/Biblioteca_Digital/Construccion/Mez...](http://anfacal.org/media/Biblioteca_Digital/Construccion/Mezclas_Repellados_y_Stuccos/AGC-
Properties_of_lime_mortar.pdf)

[http://cornishlime.co.uk/information/lime-in-
building/](http://cornishlime.co.uk/information/lime-in-building/)

Soil stabilization:
[http://www.graymont.com/sites/default/files/pdf/tech_paper/l...](http://www.graymont.com/sites/default/files/pdf/tech_paper/lime_treated_soil_construction_manual.pdf)

Hope it helps

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wowtip
Thanks, much appreciated!

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rflrob
One thing I recall reading is that rebar-reinforcing concrete is a major
factor in concrete deterioration. So while concrete structures today don't
last nearly as long as the Roman Pantheon (poured in the second century AD),
they're also really cheap to build, can go really high, and last for 40 or
more years (which given how cheap it is, the architects probably thought was
long enough).

~~~
Animats
Rebar is a big problem. But concrete without it has terrible tensile strength.
If you want to build in earthquake country, or have long concrete beams, there
has to be something with tensile strength in there.

There's stainless steel rebar.[1] That holds up well against corrosion, but
costs 8x as much as the cheap stuff. There was a fad for epoxy-coated rebar,
but it's not holding up well in practice; the coating is too fragile.

The original Panama Canal locks are holding up well after a century. But the
lock walls don't have rebar. The lock gates are all steel. The new locks have
severe concrete flaws.[2]

[1]
[https://www.youtube.com/watch?v=FrFcGx_UPow](https://www.youtube.com/watch?v=FrFcGx_UPow)
[2] [http://gcaptain.com/a-concrete-sample-was-pulled-from-the-
ne...](http://gcaptain.com/a-concrete-sample-was-pulled-from-the-new-panama-
canal-locks-and-it-does-not-look-good/)

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pitaa
This is a pet peeve of mine, and makes me want to scream every time I see some
click bait about how much better roman concrete was. If their concrete was so
great, where are the ruins of the toman skyscrapers?!? :)

~~~
fiblye
I think a big reason ancient towers didn't really exist is less because they
couldn't be built, and more that nobody wanted to climb up 5 or 10 floors if
they could avoid it. No sane person would go up and down 20 floors if they
could avoid it.

The colosseum is 150 feet tall, which isn't exactly short. Beyond that point,
I think a big problem is getting the resources up high enough to keep
building, as well as convincing people to climb that far up.

~~~
sbierwagen
The only multistory residential buildings of antiquity I know of is the old
city of Sana'a:
[https://en.wikipedia.org/wiki/Sana%27a#Old_City](https://en.wikipedia.org/wiki/Sana%27a#Old_City)
Five to nine stories tall, made of rammed earth, not even concrete! (Not
enough water for concrete in Yemen) Continuously inhabited for ~2500 years.

@idlewords went there back in 2014, before the Saudis invaded:
[http://idlewords.com/2014/07/sana_a.htm](http://idlewords.com/2014/07/sana_a.htm)

~~~
vacri
Rome had multistorey (3 to 4 of them) residential buildings, and opposite to
today, the lower floors were the prestige floors - less climbing, more robust
materials. The top floors were generally poorly constructed, out of
lightweight materials.

~~~
dankohn1
In Manhattan, buildings over 100yo have taller ceilings on the first couple
floors (where the retail shops would be and the owners would live), and then
low ceilings on the highest floors for the scriveners and production workers.
Of course, it's an issue today when lots of software companies want light
(i.e., high floor) and high ceilings.

People don't realize what a paradigm shifting technology elevators were.

~~~
caf
The Secret Life of Machines - The Lift (Elevator):

[https://www.youtube.com/watch?v=dBLa105TQeg](https://www.youtube.com/watch?v=dBLa105TQeg)

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blkhawk
Again? These Scientists must have the memory of goldfish - It seems like this
is cracked every other month in the last 5 years or so

~~~
Baeocystin
Seriously. Pozzolans and hydraulic cements have been well understood for a
very long time.

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

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dre85
This article seems to imply that only Roman marine concrete is more lasting
because of the ongoing reaction with the sea water, but I was under the
impression that all Roman concrete was more lasting... Is it just the presence
of rebar that makes today's concrete so short lived or is there something else
as well?

~~~
MrTonyD
I'm no expert, but I've read that their use of volcanic rock is a major factor
- since "pumice" has a swiss-cheese like surface, and that tends to add
strength to concrete. Also, they used incredibly little water in their
mixtures - there are descriptions of them pounding in the concrete (as opposed
to the way we "flow" it.) I understand that studies have shown that concrete
mixed with very little water is much stronger. I also read that fast-setting
concrete has been found to be very weak - and was never actually tested in any
significant way before it was approved. So very long curing times result in
much stronger concrete.

Obviously, all these discoveries are being fought by the building industry -
so none of these things are reflected in current code. Instead, they just
argue about rebar while ignoring the other discoveries.

~~~
peterwwillis
Just because it's stronger doesn't mean it's more durable, which the article
points out. Portland concrete has higher compressive strength but doesn't last
as long.

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MrTonyD
Well, old concrete, even pre-"quick set" has been found to be much more
"durable" (colloquially speaking - not really an engineering term.) And in
most applications it isn't concrete's compressive strength which causes
failure - for either old concrete or new concrete. So I would hesitate to
defend current building practices based on the lone metric of compressive
strength. But, again, I'm not a structural engineer (though I do know one who
works for the state, and he isn't allowed to express his real opinions about
the danger of our current infrastructure - many building failed in earthquakes
which they should have survived easily.)

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deepnet
I live in a limecrete building from 1857, in the Scottish Borders.

It is similar to a tower block in minature, a girder frame with cast walls,
only 3 stories high - but the rest of the village is all 2 story stone
cottages. Innovative technology for 1857 !

But being limecrete it has set into limestone over the last 150 years - a very
long lasting technology.

The only downside is it suffers from the 1960s portland-cement based harling
(pebble dash) which keeps the moisture close to the stone - hopefully we can
change this to a lime render and limewash as it should be.

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jayd16
Maybe someone in this thread will know but I've always feared Roman concrete
suffers from survivor bias.

Do we know Roman concrete was always great or are we just looking at
structures that happen to last?

~~~
folli
Aren't the structures that lasted 2000 years also the ones that are worth
taking a closer look at?

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bsder
I suspect "curing time" is probably part of the issue.

As a mental exercise, how many projects would get funding if their concrete
took 10 years to cure? So, how far down do you have to dial that before people
are willing to pay the money and how much impact does that have on
"durability"?

~~~
DrScump
This is why Hoover Dam was poured in planned, interlocking segments, with cold
water piped through it to accelerate curing.

A contiguous pour would have taken an estimated 125 years to cure, even
assuming no fatal shrinkage occurred.

~~~
kwhitefoot
Surely cooling retards curing. And it is commonly done to avoid inducing
thermal stress and causing cracks.

~~~
philjohn
Not necessarily - the reaction that produces heat is purely chemical, by
taking this heat away you're not going to stop it, but you are going to give
more headroom for the reaction to continue.

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legulere
Another interesting ancient concrete technology is using rice to form a
composite:
[https://www.acs.org/content/acs/en/pressroom/newsreleases/20...](https://www.acs.org/content/acs/en/pressroom/newsreleases/2010/may/revealing-
the-ancient-chinese-secret-of-sticky-rice-mortar.html)

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petre
Some hempcrete/hemp lime binders are also made with pozzolites.

