Why were ancient Roman concrete structures so durable

[Angela]

while ours crumble after a few decades?

I've often wondered myself, not only in terms of the roads, but more importantly the sewers and aqueduct. Some of the ones in Rome itself are still operating efficiently today. Or, just go see the Pantheon, my favorite building in the world, still gorgeous after 2000 years.

Well, MIT has discovered the answer.

See:
Riddle solved: Why was Roman concrete so durable? | MIT News | Massachusetts Institute of Technology

The answer lay in lime "clasts" found within the concrete which, while previously thought to be an example of poor mixing, actually gave the concrete "healing properties".

How on earth the Romans figured this out 2000 years ago is beyond me.

"Historically, it had been assumed that when lime was incorporated into Roman concrete, it was first combined with water to form a highly reactive paste-like material, in a process known as slaking. But this process alone could not account for the presence of the lime clasts. Masic wondered: “Was it possible that the Romans might have actually directly used lime in its more reactive form, known as quicklime?”Studying samples of this ancient concrete, he and his team determined that the white inclusions were, indeed, made out of various forms of calcium carbonate. And spectroscopic examination provided clues that these had been formed at extreme temperatures, as would be expected from the exothermic reaction produced by using quicklime instead of, or in addition to, the slaked lime in the mixture. Hot mixing, the team has now concluded, was actually the key to the super-durable nature.
“The benefits of hot mixing are twofold,” Masic says. “First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction.”
During the hot mixing process, the lime clasts develop a characteristically brittle nanoparticulate architecture, creating an easily fractured and reactive calcium source, which, as the team proposed, could provide a critical self-healing functionality. As soon as tiny cracks start to form within the concrete, they can preferentially travel through the high-surface-area lime clasts. This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material. These reactions take place spontaneously and therefore automatically heal the cracks before they spread. Previous support for this hypothesis was found through the examination of other Roman concrete samples that exhibited calcite-filled cracks."
To prove that this was indeed the mechanism responsible for the durability of the Roman concrete, the team produced samples of hot-mixed concrete that incorporated both ancient and modern formulations, deliberately cracked them, and then ran water through the cracks. Sure enough: Within two weeks the cracks had completely healed and the water could no longer flow. An identical chunk of concrete made without quicklime never healed, and the water just kept flowing through the sample. As a result of these successful tests, the team is working to commercialize this modified cement material.

[italouruguayan]

absolutely admirable...

[torzio]

maybe it was the huge amount of Lime they used with their cement .......just a guess

https://en.wikipedia.org/wiki/Lime_(material)

[bicicleur 2]

Roman structures are monumental
concrete structures today are armed with iron in order to accomodate tensile stress
constructions today are much lighter and bridge spans are much longer
I don't think you should drive 10 ton trucks over the old aquaducts every day ..

it would be nice though if new applications could be developped for some purposes with a Roman formula

[bicicleur 2]

https://en.wikipedia.org/wiki/Pozzolan

the name Pozzolan is derived from the Italian city Pozzuoli in the Bay of Naples
this concrete would have formed naturaly under the sea level because of the local Volcanic activities

I wonder why MIT comes up with this now, this was known long before ..

[Angela]

@Bicicleur and Torzio.

It's not about that. They specifically address that issue and say it doesn't explain it.

It's about a different process.

Helps to read at least the whole post if the article is too long, people.

Unless the problem is reading comprehension?

[bicicleur 2]

@Bicicleur and Torzio.

It's not about that. They specifically address that issue and say it doesn't explain it.

It's about a different process.

Helps to read at least the whole post if the article is too long, people.

Unless the problem is reading comprehension?

I've only read it in diagonal but :

This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material. These reactions take place spontaneously and therefore automatically heal the cracks before they spread.

These are the reactions that take place under sea level in the Bay of Naples. It makes it possible to form concrete or cement under water.

But I'm sure, if MIT wants to spend money to investigate further, they are up to something further.

[bicicleur 2]

Along with other new formulations, such as concrete that can actually absorb carbon dioxide from the air, another current research focus of the Masic lab, these improvements could help to reduce concrete�s global climate impact.

There is allready a pilot production of such material in Belgium :

https://www.brusselstimes.com/338353/limburg-company-produces-building-blocks-from-co2

their prime material is a waste product form stainless steel producers
they are optimizing the production method to license it wherever stainless steel is being produced all around the world

[bicicleur 2]

The properties of hardened blended cements are strongly related to the development of the binder microstructure, i.e., to the distribution, type, shape and dimensions of both reaction products and pores. The beneficial effects of pozzolan addition in terms of higher compressive strength, performance and greater durability are mostly attributed to the pozzolanic reaction in which calcium hydroxide is consumed to produce additional C-S-H and C-A-H reaction products. These pozzolanic reaction products fill in pores and result in a refining of the pore size distribution or pore structure. This results in a lowered permeability of the binder.

So MIT says the Romans used quicklime, which is calcium oxide instead of letting calcium hydroxide do the job.

However :

One of the principal reasons for increased durability is the lowered calcium hydroxide content available to take part in deleterious expansive reactions induced by, for example, sulfate attack.


We'll see what comes out of the MIT research.

[Angela]

Also, the Pantheon doesn't have metal rods to keep it standing, but it's still going strong 2000 years later. I'm sure if they examine a piece of the concrete they'll find those same "clasts".

Another interesting feature is that they solved the problem of not having the building settle over the centuries without beams going down to bedrock.




"Unrecognized, the design of this ancient concrete building reveals unparalleled features not encountered in modern design standards. Recent studies reveal several major cracks in the dome, but it still functions unimpaired. This condition will surely excite the curiosity of our structural engineers. The building was built entirely without steel reinforcing rods to resist tensile cracking, so necessary in concrete members, and for this concrete dome with a long span to last centuries is incredible. Today, no engineer would dare build this structure without steel rods! Modern codes of engineering practice would not permit such mischief. No investor with knowledge of concrete design would provide the funding. Additional constraints when attempting to build a structure as large as the Pantheon will be discussed later, but briefly they include the use of inadequate hand tools and unsafe lifting devices. I believe we can learn from this activity. Workers can build from a plan and can successfully use their proven practices only if construction quality controls are maintained."

As for Roman roads, I've walked on many, including the Via Appia Antica. Others have been covered over by a layer of concrete, such as the Via Emilia, on which I travel by car often (S 49). That concrete surface crumbles, but not what is underneath. Here it is within the city of Modena, where they have left it alone.


Ancient Roman Roads | Facts, Construction & History | Study.com

On to bridges:

The Puente Romano Bridge in Merida Spain was only pedestrianized in 1991. Whether there were weight restrictions I don't know.


It would seem to me that "self-healing" concrete would be of inestimable use to us today, as well as, according to the authors, more environmentally friendly.

[Angela]

I've only read it in diagonal but :

This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material. These reactions take place spontaneously and therefore automatically heal the cracks before they spread.

These are the reactions that take place under sea level in the Bay of Naples. It makes it possible to form concrete or cement under water.

But I'm sure, if MIT wants to spend money to investigate further, they are up to something further.

As I said, perhaps it's reading comprehension in a language not one's own, which is understandable.

The OR is important. Just reacting with water creates the recrystallization as calcium carbonate and then fill the crack.

Perhaps, if you haven't, you should read the entire article, such as where they state that this is NOT a question of the pozzolanic materials upon which you are fixated.

Is it so difficult for you to admit the genius of the Romans in engineering, so that you have to insist the remarkable durability was down to a natural process and not the use of a new technique?

You, and others, say I have to get over the destruction and death caused by the Germans to my country and my family, even to sending my mother's cousin to a concentration camp because it happened 80 years ago. Well, the conquest of your country by the Romans was 2000 years ago, Bicicleur. I've certainly gotten over their conquest and enslavement of the Ligures. Give it a rest.

"

[real expert]

.........
You, and others, say I have to get over the destruction and death caused by the Germans to my country and my family, even to sending my mother's cousin to a concentration camp because it happened 80 years ago. Well, the conquest of your country by the Romans was 2000 years ago, Bicicleur. I've certainly gotten over their conquest and enslavement of the Ligures. Give it a rest.

"

Of course, as someone who is a descendant of people who were directly affected by the atrocities committed by Germany, you can't just let go and move on. There are wounds and traumas from the past that can't really heal. So I don't blame you for developing a dislike, if not hatred, for Germans from that time period. You can't, however, hold a grudge against everyone with Germanic ancestry, especially those born after WWII who are not responsible for what their ancestors did. Moreover, how can you blame ancient Germanic people from 2000 years ago for what their descendants did thousands of years later? Remember that Mussolini's Italy, your own country, was an ally of Nazi Germany. And even after the Italians switched sides, the northern part of Italy was still an ally of the Germans and even collaborated with them to kill fellow Italians who resisted the Nazis. Having said that, the Italians were smarter and wiser than the Germans in that they got rid of Mussolini and hanged him, as opposed to the Germans, who remained loyal to Hitler until the end. Besides, the Romans were perfectionists, and the Roman Empire was one of the most technologically advanced civilizations of antiquity. So it makes perfect sense that they produced high-quality and very durable concrete. Give credit where credit is due.

[bicicleur 2]

As I said, perhaps it's reading comprehension in a language not one's own, which is understandable.

The OR is important. Just reacting with water creates the recrystallization as calcium carbonate and then fill the crack.

Perhaps, if you haven't, you should read the entire article, such as where they state that this is NOT a question of the pozzolanic materials upon which you are fixated.

Is it so difficult for you to admit the genius of the Romans in engineering, so that you have to insist the remarkable durability was down to a natural process and not the use of a new technique?

You, and others, say I have to get over the destruction and death caused by the Germans to my country and my family, even to sending my mother's cousin to a concentration camp because it happened 80 years ago. Well, the conquest of your country by the Romans was 2000 years ago, Bicicleur. I've certainly gotten over their conquest and enslavement of the Ligures. Give it a rest.

"

In this post I told I had only read diagonaly. I even added I guessed there was something more.
I've done some further reading and made some more posts.
Did you read all of my posts?

If I'm wrong in my conclusion, just tell me.
I don't know why you drag in de Bello Gallico, the Ligurians and WW II.

[Angela]

In this post I told I had only read diagonaly. I even added I guessed there was something more.
I've done some further reading and made some more posts.
Did you read all of my posts?

If I'm wrong in my conclusion, just tell me.
I don't know why you drag in de Bello Gallico, the Ligurians and WW II.

I drag it in because your bias is so glaringly obvious.

Have you read all my posts? I have pointed out your errors in reading comprehension. Did you read the article??? This is not about volcanic ash from the Bay of Naples. It is about a HOT mixing technique.

It was no doubt used in the Pantheon, which contains the largest unsupported dome in the world.

I don't know how much more clearly it can be said. I even pointed out the conjunction, "or", which you disregarded. What more am I supposed to do?

I give you chance after chance, because I know you have knowledge which might be useful, but all exchanges with you end like this.

So, I'm done.

[Angela]

Of course, as someone who is a descendant of people who were directly affected by the atrocities committed by Germany, you can't just let go and move on. There are wounds and traumas from the past that can't really heal. So I don't blame you for developing a dislike, if not hatred, for Germans from that time period. You can't, however, hold a grudge against everyone with Germanic ancestry, especially those born after WWII who are not responsible for what their ancestors did. Moreover, how can you blame ancient Germanic people from 2000 years ago for what their descendants did thousands of years later? Remember that Mussolini's Italy, your own country, was an ally of Nazi Germany. And even after the Italians switched sides, the northern part of Italy was still an ally of the Germans and even collaborated with them to kill fellow Italians who resisted the Nazis. Having said that, the Italians were smarter and wiser than the Germans in that they got rid of Mussolini and hanged him, as opposed to the Germans, who remained loyal to Hitler until the end. Besides, the Romans were perfectionists, and the Roman Empire was one of the most technologically advanced civilizations of antiquity. So it makes perfect sense that they produced high-quality and very durable concrete. Give credit where credit is due.

I have never said that I feel dislike for Germans born after WWII because of the atrocities committed during the war. I do think, however, that we find people from different cultures more or less agreeable, and that's a right we all have. I have a friend, Irish-American, who was in my study group in law school, married to an Italian-American girl, who doesn't much find Italy agreeable. Knowing his character, I understand why. It doesn't affect our friendship. He's entitled to his opinion, although I of course don't want to hear ad infinitum, which he obviously understands.

I'd point out that since even my mother was a tiny child during the last of the war years, these are not personal experiences. They are transmitted stories, like the one about my mother's much older second cousin being sent to the camps for anti-German activity in the factories, or her memory of the bodies of villagers killed in reprisal for partisan activity hanging from the tree outside the church, men and women both, or her watching her uncle and the young men on his farm hiding in shelters carved into the vineyard terraces to escape the SS patrols looking for slave labor to send to Germany, and also for all their food. One of her worst memories, along with the hanging bodies, was of her uncle having to cut off a man's leg on their dining room table with rags in his mouth to prevent him from making any noise. Until her dying day, she left the room or asked for the show to be turned off if people were speaking German on tv.

Can trauma be transmitted in this way, or by even more horrific stories told me by great uncles and aunts and my father's parents?

I don't know if you could call it trauma, but I can tell you that I had nightmares about scenes like that, and about the stories recounted by great uncles and aunts and my father's parents about peasants herded into churches with their priests and then set alight, or women bayonetted in their pregnant bellies or babies swung by their feet against stone walls. The blood is still there.

They didn't deliberately tell me these things, btw, but children are all ears even if the stories are told in hushed tones.

Then, there was really no hiding it since there are monuments everywhere.

I didn't forgive or forget, and because of that I worked as much as I could during my visits and from here on legal attempts to extradite the Germans who committed war crimes in my father's villages, and my mother's. All to no avail. Germany would not release them, so there's that about Germans born after the war.

If you wish to read further about the matters of which I speak I highly recommend the much-admired book called "Silence on Monte Sole". .

I'd also point out that perhaps you're unaware that there was a civil war in Italy after the withdrawal from the alliance with Germany and the creation of the state of Salo'. By no means all or even a majority of Italians supported the latter. In northwestern Italy, in particular, there was a long history of Socialism and Anarchism, anti-Royalism, and as a consequence, anti-fascism. I have joked before that people imbibed it with their mother's milk. They were never fascists by choice. In fact, the city of Sarzana, a stone's throw from me, and Parma, in my father's ancestral homeland, were the last Italian towns to accept fascism, and it was done by force. I'm not aware of anything remotely similar occurring in Germany in the 20s and 30s.
https://www.marxists.org/history/eto...no2/rossi.html

Most Italians in general, of course, while being against Mussolini and Salo by this point, particularly because of the fact that some of the committed Italian fascists assisted the SS in their atrocities, for which many of them paid dearly later on, and because they and the SS forcibly conscripted young men into the forces of a state they despised, just tried to keep their heads low and survive, which was, of course, the sensible choice.

It takes an almost insane kind of courage most people don't have to go against the SS Einsatzgruppen fresh from their atrocities in Eastern Europe with an old hunting rifle and a few arms dropped by the English. Yet, there were those who did it. One of my great-aunts married a partisan in a white dress made from the silk of a parachute. I have her wedding purse made of the same material.

[bicicleur 2]

I drag it in because your bias is so glaringly obvious.

Have you read all my posts? I have pointed out your errors in reading comprehension. Did you read the article??? This is not about volcanic ash from the Bay of Naples. It is about a HOT mixing technique.

It was no doubt used in the Pantheon, which contains the largest unsupported dome in the world.

I don't know how much more clearly it can be said. I even pointed out the conjunction, "or", which you disregarded. What more am I supposed to do?

I give you chance after chance, because I know you have knowledge which might be useful, but all exchanges with you end like this.

So, I'm done.

Oh, you're teaching me a lesson, because I don't understand the article.
Well, just tell me how the hot mixing was done.
I'll give you a clue.
Check my post #9. It tells how the heat was provoked.

If you can't answer me, you're the one who can't read.

Yes, I don't care about glorifying or not glorifying the acomplishments of the Roman Empire, I only wanted to know which is the secret these guys from MIT try to unravel.
Now I understand it, but I have the impression you don't.
Maybe I'm wrong.
I'll give you a few days to reveal the secret, and then I'll do it myself.

[Angela]

Oh, you're teaching me a lesson, because I don't understand the article.
Well, just tell me how the hot mixing was done.
I'll give you a clue.
Check my post #9. It tells how the heat was provoked.

If you can't answer me, you're the one who can't read.

Yes, I don't care about glorifying or not glorifying the acomplishments of the Roman Empire, I only wanted to know which is the secret these guys from MIT try to unravel.
Now I understand it, but I have the impression you don't.
Maybe I'm wrong.
I'll give you a few days to reveal the secret, and then I'll do it myself.

Here is the link to the paper. If after you have read it you still think you know better than the engineers at MIT, I suggest you contact them and impart your greater knowledge.
Hot mixing: Mechanistic insights into the durability of ancient Roman concrete | Science Advances

As for me, I won't read your pearls of wisdom because you're back on ignore, where you join Torzio, Northerner and I Don't Know What I'm Doing, who really doesn't know what he's doing.

[traveller]

Using quicklime directly in construction is pretty dangerous and unpredictable.

Quicklime absorbs moisture really well. While doing that, it heats up, expands and changes its properties (converts into hydrated lime). So, there are huge issues in transporting and handling the material. The Romans were probably creating lime onsite by building and operating a lime kiln. This process of burning limestone may take a week, and the hydration of lime pits took up to a year. I would guess if one would build with quicklime, the structure needs to be kept soaked for a long time as well. Then again, for the self-healing process to work, should it be only partially hydrated?

I can imagine this process during factory construction of prefabricated elements, but even there the curing/stabilization time needs to be shortened. While the Pantheon may have been built in decade or two, I doubt many buildings can be built this slowly in our time.

[bicicleur 2]

Here is the link to the paper. If after you have read it you still think you know better than the engineers at MIT, I suggest you contact them and impart your greater knowledge.
Hot mixing: Mechanistic insights into the durability of ancient Roman concrete | Science Advances

As for me, I won't read your pearls of wisdom because you're back on ignore, where you join Torzio, Northerner and I Don't Know What I'm Doing, who really doesn't know what he's doing.

I don't need the paper, it is in the article itself.
The reaction with quicklime is exotherm, which means it produces heat.
Traveller knows a lot about this stuff, much more than me. He explained it perfectly in his post.
You're the one talking about things you don't understand.
And you consider everyone who tells something you don't like or who doesn't go along in gloryfying the Roman Empire a dumb ignorant not worth talking to.
I don't understand how someone intelligent like you can be so biased.

[bicicleur 2]

Using quicklime directly in construction is pretty dangerous and unpredictable.

Quicklime absorbs moisture really well. While doing that, it heats up, expands and changes its properties (converts into hydrated lime). So, there are huge issues in transporting and handling the material. The Romans were probably creating lime onsite by building and operating a lime kiln. This process of burning limestone may take a week, and the hydration of lime pits took up to a year. I would guess if one would build with quicklime, the structure needs to be kept soaked for a long time as well. Then again, for the self-healing process to work, should it be only partially hydrated?

I can imagine this process during factory construction of prefabricated elements, but even there the curing/stabilization time needs to be shortened. While the Pantheon may have been built in decade or two, I doubt many buildings can be built this slowly in our time.

Thank you traveller.

If I understand this correctly, it is a matter to controll the progress of the reaction of the quicklime with water.
And at some point this reaction should be stopped, maybe by a shortage in moisture, so it can infiltrate and start again in the cracks when they become wet again?
The quicklime should be mixed and dispersed very well in the concrete.

I've first heared about this in self-healing fibre-reinforced polymer composites, which are very prone to cracks.
https://en.wikipedia.org/wiki/Self-healing_material

[traveller]

Thank you traveller.

If I understand this correctly, it is a matter to controll the progress of the reaction of the quicklime with water.
And at some point this reaction should be stopped, maybe by a shortage in moisture, so it can infiltrate and start again in the cracks when they become wet again?
The quicklime should be mixed and dispersed very well in the concrete.

I've first heared about this in self-healing fibre-reinforced polymer composites, which are very prone to cracks.
https://en.wikipedia.org/wiki/Self-healing_material

Thanks for the link!

Apparently the quicklime particles have to be big enough not to hydrate completely.

DB821C40-067E-4E5F-82C2-5D9985374712.jpg

This is a different process from the Roman undersea concrete:

“Whereas previous evidence supports the formation of Al-tobermorite minerals in lime clasts of maritime structures due to the heat of the pozzolanic reaction (23), the results presented here suggest that, by contrast, when quicklime is introduced via hot mixing in terrestrial structures, the reaction is limited to the outer rim of the lime clast, encapsulating calcium-rich core structures within mortar matrix.”

It would require particle sizes that are “just right” to stay active over a long period but not jeopardize the strength and dimensions of the concrete/mortar, as well as much finer particles or prehydrated lime to achieve initial strength. Actually, using this as mortar to bind stones in a wall massive enough to be stable on its own might make more sense than a big chunk of concrete.

Still, I don’t think the self-healing can last through a longer period of crack formation as at some point all the active lime would be spent.

[traveller]

The healing effect may also be unintended and just a consequence of imperfect grinding/hydration/mixing.

[bicicleur 2]

The healing effect may also be unintended and just a consequence of imperfect grinding/hydration/mixing.

yes, I would guess so

however the Roman engineers may have been smart enough to notice this effect and have kept the recipee

I guess there are no written sources on this and this kind of knowledge was transferred from master to apprentice in practice

[bicicleur 2]

Thanks for the link!

Apparently the quicklime particles have to be big enough not to hydrate completely.

DB821C40-067E-4E5F-82C2-5D9985374712.jpg

This is a different process from the Roman undersea concrete:

“Whereas previous evidence supports the formation of Al-tobermorite minerals in lime clasts of maritime structures due to the heat of the pozzolanic reaction (23), the results presented here suggest that, by contrast, when quicklime is introduced via hot mixing in terrestrial structures, the reaction is limited to the outer rim of the lime clast, encapsulating calcium-rich core structures within mortar matrix.”

It would require particle sizes that are “just right” to stay active over a long period but not jeopardize the strength and dimensions of the concrete/mortar, as well as much finer particles or prehydrated lime to achieve initial strength. Actually, using this as mortar to bind stones in a wall massive enough to be stable on its own might make more sense than a big chunk of concrete.

Still, I don’t think the self-healing can last through a longer period of crack formation as at some point all the active lime would be spent.

what is carbonation, and does it promote the infiltration of water into the encapsulated quicklime particle?

[traveller]

what is carbonation, and does it promote the infiltration of water into the encapsulated quicklime particle?

Actually it’s carbonatation - the hardening of lime. See https://en.wikipedia.org/wiki/Carbonatation

They found that the whole particle doesn’t carbonatate and this the center remains active. It’s weaker than the surroundings, which encourages cracks to split the particle.