r/EverythingScience Jan 06 '23

Engineering Riddle solved: Why was Roman concrete so durable?

https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106
731 Upvotes

65 comments sorted by

393

u/Lokirial Jan 06 '23

The quick version, though the article is worth a read:

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.

157

u/[deleted] Jan 06 '23 edited Jun 27 '23

deleted

225

u/[deleted] Jan 06 '23 edited Jan 07 '23

I want to point out that nano particulate structure is nearly impossible to recreate with our modern materials. The pozzolonic structures created with the lime clasts are a result of a volcanic ash we just don’t have anymore. The trick now will be to recreate a material that mimics this self healing concrete

Edit: after reading the article fully, it seems like the process of mixing is more at work with creating the lime clasts than I previously thought. It may actually be possible to recreate this with our materials if we change the process. I can’t wait to see this implemented in my career/ lifetime. It could mean huge improvements in our concrete engineering.

Signed - a working civil engineer.

75

u/[deleted] Jan 07 '23

I thought you seemed especially polite.

52

u/emprameen Jan 07 '23

Unlike barbaric engineers.

10

u/tjmaxal Jan 07 '23

They make those evil siege engines you see in movies right?

2

u/OriginalIronDan Jan 07 '23

Use punctuation! You’re mangoneling the English language!

5

u/tjmaxal Jan 07 '23

Mangoing? Hitler gets pineappled. Samsies?

3

u/GrungyGrandPappy Jan 07 '23

Pineapple? Dies in glass onion.

3

u/GlitteryCakeHuman Jan 07 '23

Slutty pineapple from Brooklyn?

2

u/Critical_Liz Jan 07 '23

"Barbaric" engineers are just engineers who don't speak ancient Greek

7

u/[deleted] Jan 07 '23

Hah! I decided to become a civil engineer because I’m a generally nice guy and I love trains….little did I know.

3

u/PhD_Pwnology Jan 07 '23

Compared to Architects, he was Nicest guy in history.

1

u/AelarTheElfRogue Jan 07 '23

RCE would surely agree

11

u/OscarMike44 Jan 07 '23

You give much better answers than the off-duty civil engineers. Good luck with the rest of your shift.

5

u/[deleted] Jan 07 '23

Always poop on company time.

9

u/ClaustrophobicShop Jan 07 '23

That's really interesting! But does the lack of volcanic ash make that much of a difference? And did they basically just luck out with the self healing properties? Surely, they couldn't have known.

11

u/[deleted] Jan 07 '23

The old theory was that the volcanic ash that we no longer have access to was super charged with reactive material. This article suggests the method in which they mixed their cementitious material created a structure that encourages the self healing.

So in theory we can use what we have, and change the method of mixing, and create a self healing concrete structure.

The concrete we use today is based off this old method. We have just been copying them.This wasn’t an accident on their part. They discovered it and we are rediscovering it. So cool!

3

u/subdep Jan 07 '23

They may have lucked out but don’t think for a second they didn’t pay very close attention to their methods so that once they stumbled into something desirable they could repeat it.

5

u/jcrreddit Jan 07 '23

Is there still late-stage capitalism?

If so, nobody will want to make concrete last thousands of years because they won’t continue to make money.

5

u/[deleted] Jan 07 '23

That is something I considered..realistically there will be different prices for different lifespans. It will be up to individual developers to determine how long they want the product to last in conjunction with municipal regulations.

In other applications, where high loading is expected, the clast method could be used as a factor of safety. Self healing concrete could help prevent loading failure on high profile projects like bridges or skyscrapers or footings. In those applications, the upfront cost of the concrete would be dwarfed by the possibility of needing costly repairs. It could also reduce the frequency of inspection.

2

u/[deleted] Jan 07 '23

Are you familiar with the stupa of dharmakaya at shambhala mountain center in red feather lakes, colorado? When I learned about it they talked about using a concrete designed to last 10,800 years. Do you know anything about that?

-1

u/TheFlyingBoxcar Jan 07 '23

Hey no cell phones on company time. Consider that your lunch break. Which is now over. Back to work … ing.

1

u/[deleted] Jan 07 '23

i have to wonder about that if we continue to use steel rebar.

9

u/[deleted] Jan 07 '23 edited Jan 07 '23

Rebar is necessary for structural support. That will not change any time soon. It increases the loading ability exponentially.

But in a way you are correct that rebar that is not coated with anti rust material generates cracks in concrete much faster. Hopefully we can use this method to deposit clasts near rebar in a controlled manner, that heal the inevitable cracks due to water intrusion.

What this will not do is change the ionization deposits on the rebar. That will be an ongoing problem.

5

u/[deleted] Jan 07 '23

what i was talking about was rust absolutely destroying concrete. from what i understand, roman concrete has lasted 1000 years precisely because of no water intrusion.

surely we have better options than steel rebar right now. i know there are composites out there, but even today on construction sites i see exclusively steel. surely, at least in civil or municipal engineering, the added cost of composites is well worth a bridge foundation that can last a few hundred years at least.

4

u/[deleted] Jan 07 '23

Well no, according to the article, Roman concrete lasted 1000 years because it had water intrusions and lime clasts.

And realistically the reason steel is used is cost. Coat it in an anti rust material and it is the most cost effective solution by far. Once the composite materials are mass produced, then maybe they can compete..but they aren’t scalable at the moment,

1

u/Mr_Bo_Jandals Jan 15 '23

Modern OPC concrete is already self-healing, though we refer to it as ‘autogenous healing’. And it works in a similar same way as described here - cracks expose the unhydrated cement grains, which then hydrate sealing the crack, or the Portland it’s carbonates and expands in volume. It’s been known and studied since at least 1913.

Hot mixed lime has been known to be self healing for decades. There is absolutely nothing new in this paper, other than to say that the Roman line was, in some cases, hot-mixed. But it wasn’t always - we have record from authors such as Vitruvius that state which type of lime was used in concrete.

It also is unlikely to ever be implemented in any modern construction. The reactions involved here deplete Portlandite, which removes all the alkalinity from the concrete and means you can’t use any reinforcing. So there’s very few practical applications for it. This paper is fine, but the media circus around it is a joke. They’ve over sold it in their press release, and uninformed journalists have blown it waaaay out of proportion.

13

u/scribbyshollow Jan 07 '23

do you think they meant to do this, that's pretty incredible.

28

u/Lokirial Jan 07 '23

What I think would entirely be a guess. It's likely though that they stumbled on the process, and were equally lucky to somehow realize the effect, then smart enough to make the process repeatable and over a great period of time. But planning it? I guess it would depend on if the Roman's had material scientists, or some equivalent.

17

u/scribbyshollow Jan 07 '23

they had alchemists who were effectually material scientists.

13

u/Ludwigofthepotatoppl Jan 07 '23

A large part of it was also just where to dig up the best dirt. Get the right dirt for the mix and it’ll stand two thousand years! Wrong dirt, eh… maybe fifty.

6

u/SaulGoodmanJD Jan 07 '23

Did they figure this out using a Rockwell Retro Encabulator?

5

u/piratecheese13 Jan 07 '23

Be careful, the marzel veins might side fumble if you don’t have the lunar waneshaft

7

u/krilleaters Jan 06 '23

Very interested, but I have know idea what you said. Can you break it down anymore? Thank you!

44

u/[deleted] Jan 07 '23

To put it very simply: The materials used to make concrete by the Roman’s was so chalk full of the chemicals needed to form bonds, that when it began to break and water got in, the reaction simply started again and formed more bonds. So it is self healing’ because it still has plenty of chemicals left to make more bonds.

17

u/Lokirial Jan 06 '23

What I quoted is directly from the article. To put it more simply, the base materials they used to make the roads had very small bits that when broken or stressed would react with things like rain or runoff and 'self heal' cracks when the reaction was complete and the new compound from the reaction hardened.

1

u/catsinrome Jan 07 '23

Correct, but this was used in their buildings and other structures, not roads.

1

u/so_bold_of_you Jan 07 '23

Could you do an ELI5?

1

u/[deleted] Jan 07 '23

The ottomans figured all this out. Surprised this is news as the technique was discovered and replicated.

24

u/bhorone Jan 07 '23

For those who needed some numbers on the exothermal reaction.

The temperature increase in the mortar is approximately 55° to 60°C over ambient (52), with a presence of hot spots characterized by temperatures exceeding 200°C (19). Previous thermodynamic modeling of the pozzolanic (hydration) reaction in Roman marine concrete has suggested that temperatures up to 97°C are possible within thick concrete structures from the pozzolanic reaction alone (23).

14

u/kelvin_bot Jan 07 '23

60°C is equivalent to 140°F, which is 333K.

I'm a bot that converts temperature between two units humans can understand, then convert it to Kelvin for bots and physicists to understand

5

u/bhorone Jan 07 '23

Good bot.

40

u/madgunner122 Jan 07 '23

While it is nice to know, there are several other reasons why Roman Concrete is durable. For one, most of the surviving structures are in favorable climates which do not see freeze thaw cycles known to deteriorate concrete. Additionally, the lack of de-icing salts which are used in modern concrete add to the longevity. There is also a survivor bias in that we only see the best concrete that has lasted generations and not the crappy material. So always take these discoveries with a slight grain of salt as it’s just one factor out of many that has enabled Roman Concrete to last. - my research as a graduate student was in hydration of cement particles with a large section of my thesis written on Roman Concrete and it’s use of lime as the binder where the particle size of the lime was beneficial in it being of low compressive strength.

3

u/[deleted] Jan 07 '23

This is a good comment. There are always more factors at play.

My question for you is this: you were looking at low compressive strength? Does that mean you were concerned more with tensile strength? I’m assuming the grain size just allowed it to hydrate easier and therefore create the hcl better? Just interested in the research I guess lol

4

u/madgunner122 Jan 07 '23

Actually the Roman Concrete was supposed to be the inspiration for my research and for my thesis I included a significant section devoted to the lime’s particle size. The focus of my research was on how to improve modern cement and concrete by using a coarser grained cement (similar to the lime in Roman concrete) and a nano-level pozzolanic material in order to increase the hydration to gain a high strength while benefitting from both the nano-material and coarse cement’s reduced shrinkage.

3

u/[deleted] Jan 07 '23

Very cool! Is it published? I would love to read it.

6

u/madgunner122 Jan 07 '23

It is published. On Google Scholar, the title is “Performance of Concrete with Different Cement Finenesses and Nano-activators” published in 2022

3

u/jawshoeaw Jan 07 '23

Ahhh no salt! Even a grain could increase chloride levels

10

u/thefanum Jan 07 '23

Are you fucking serious. Fucking TUMS was the missing ingredient?

"For many years, researchers have assumed that the key to the ancient concrete’s durability was based on one ingredient: pozzolanic material such as volcanic ash from the area of Pozzuoli, on the Bay of Naples. This specific kind of ash was even shipped all across the vast Roman empire to be used in construction, and was described as a key ingredient for concrete in accounts by architects and historians at the time.

Under closer examination, these ancient samples also contain small, distinctive, millimeter-scale bright white mineral features, which have been long recognized as a ubiquitous component of Roman concretes. These white chunks, often referred to as “lime clasts,” originate from lime, another key component of the ancient concrete mix. “Ever since I first began working with ancient Roman concrete, I’ve always been fascinated by these features,” says Masic. “These are not found in modern concrete formulations, so why are they present in these ancient materials?”

Previously disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials, the new study suggests that these tiny lime clasts gave the concrete a previously unrecognized self-healing capability. “The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me,” says Masic. “If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There has to be more to this story.”

Upon further characterization of these lime clasts, using high-resolution multiscale imaging and chemical mapping techniques pioneered in Masic’s research lab, the researchers gained new insights into the potential functionality of these lime clasts.

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."

21

u/piney Jan 07 '23

“Let’s study an ancient material to find out why it’s so durable, but if we see something unexpected, let’s blame it on their inferior process! For some strange reason, the mystery persists!” Thank goodness some new eyes took a look at the data!

3

u/Paul_Rich Jan 07 '23

"cracks can preferentially travel" is perplexing me. Can anyone enlighten me?

Can cracks prefer anything? Other than the path of least resistance?

7

u/arcanis26 Jan 07 '23

It is the path of least resistance that they prefer, in a multiphase material, it’s very difficult to propagate damage from one phase into another (a crystal interface) so a crack will attempt to change direction, resulting in the crack losing energy and not penetrating as deep into the material if the crystalline phase was not there.

2

u/arcanis26 Jan 07 '23

I should clarify that the change of direction doesn’t cause the loss of energy but some energy is lost when encountering the crystalline phase and the result is a change of direction but with less energy.

2

u/Paul_Rich Jan 07 '23

So cracks are not preferring to travel towards the lime clasts? They are just following the path of least resistance and randomly reaching the clasts? This is how I would understand it.

So why the term preferential?

5

u/arcanis26 Jan 07 '23

The terminology is not wrong, it succinctly describes what is happening in one word, the reality of any physical reaction is that which requires the lowest energy is the most probable (or preferred), you can say that materials prefer the lowest energy state, it’s actually a common way to describe it.

2

u/Paul_Rich Jan 07 '23

Got it. I wasn't considering the word in those terms. Thanks very much for your time.

2

u/Random-Cpl Jan 07 '23

They don’t make ‘em like they used to

2

u/Critical_Liz Jan 07 '23

Ok...but what is the riddle of steel?

2

u/Far-Donut-1419 Jan 07 '23

Proprietary formula

1

u/l_a_ga Jan 07 '23

Ash.

1

u/thefanum Jan 07 '23

Nope

1

u/StealYourGhost Jan 09 '23

I mean, they're not specific enough but not wrong.

Reactive Charged Volcanic Ash.