Riddle solved: Why was Roman concrete so durable?

[Nevilledog]

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

The ancient Romans were masters of engineering, constructing vast networks of roads, aqueducts, ports, and massive buildings, whose remains have survived for two millennia. Many of these structures were built with concrete: Rome’s famed Pantheon, which has the world’s largest unreinforced concrete dome and was dedicated in A.D. 128, is still intact, and some ancient Roman aqueducts still deliver water to Rome today. Meanwhile, many modern concrete structures have crumbled after a few decades.

Researchers have spent decades trying to figure out the secret of this ultradurable ancient construction material, particularly in structures that endured especially harsh conditions, such as docks, sewers, and seawalls, or those constructed in seismically active locations.

Now, a team of investigators from MIT, Harvard University, and laboratories in Italy and Switzerland, has made progress in this field, discovering ancient concrete-manufacturing strategies that incorporated several key self-healing functionalities. The findings are published today in the journal Science Advances, in a paper by MIT professor of civil and environmental engineering Admir Masic, former doctoral student Linda Seymour ’14, PhD ’21, and four others.

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.

*snip*

[sakabatou]

1. I wonder why hot mixing isn't used to much for things

like sidewalks, driveways, or other civilian projects.

[Laura PourMeADrink]

9. Great question! We were just talking about growing up and seeing all those cement trucks

With the backs turning. And how we don't see them anymore. Assume there was heat in there?

[Rebl2]

11. Really?

I see them quite often. I don’t know if there is heat involved though.

[Laura PourMeADrink]

27. Lol. Okay now I'm going to have to start looking for them. Maybe we don't live

Cement plant anymore

[Rebl2]

30. I live on

a main road in my town so I see them go by on there way to wherever.

[Laura PourMeADrink]

31. There you have it. !!!

[Laura PourMeADrink]

32. Oh Lordie. When I see the flag I think trump. Maybe that's

what our mission should be - to take back the flag!

[jmowreader]

16. Only if you're pouring concrete in cold weather do you want to mix hot

It sets up too damned fast if you use hot water in nice weather. Concrete doesn’t harden by drying, it cures by chemical reaction. If it sets up too fast the reaction doesn’t get time to run to completion, and the finished piece becomes weaker.

[soldierant]

25. According to the full article,

they didn't use hot water. They used quicklime along with slaked (wet) lime to produce a thermal reaction to get the heat. This also changed the form of the calcium carbonate to provide a "self-healing" feature - if for instance there was a crack anf water got i, the calcium carbonate would move to fill the crack.

[onethatcares]

26. which makes sense

modern concrete also uses a lot of iron rebar that once it contacts water it begins to rust and expand allowing more water and more expansion.

I don't think the Romans used rebar.

[soldierant]

33. I'm pretty sure you're right.

Did it even exist? I doubt it.

[RainCaster]

2. Thank you for sharing this

A truly interesting article.

[secondwind]

3. Very interesting. Masic has an impressive background.

Born in Croatia….

[albacore]

4. I always wondered...

The Pantheon.. the aqueducts...
Makes perfect sense.

[GenThePerservering]

5. Thank you!

I saw the durability of Roman building and engineering when I hiked the length of Hadrian's Wall in the north of England. The only thing that broke down that wall was Anglo-Saxon and Medieval poaching. Not only is the concrete durable, but one can still see the elements such as where door hinges were embedded in it. It's fascinating to now know the science behind this.

Even today Italian builders are traditionally some of the best around.

[keithbvadu2]

6. Lost technology found again.

Somebody back then figured it out.

[byronius]

7. Yah, great post.

[SWBTATTReg]

8. This is going to be major!

[Pinback]

10. Very cool - thanks.

Remember, too, that the actual workmanship was likely done by slaves, working at the direction of Roman engineers and overseers. I’ve read about the Roman Empire having different classes of slaves, including skilled artisans, some of whom were able to eventually buy their freedom and become citizens.

Fascinating society, and despite its flaws, one with a legacy of astonishing achievements.

[Mr. Sparkle]

12. I love stories like these.

Thanks for posting

[erronis]

13. This is the way a post should be done. Post links to the references and include some abstracts.

Thank you Neville Dog. I always know I'll learn something interesting from you. And many others that don't just post a non-descript title and a link to a twit.

[Alexander Of Assyria]

17. Yes. The link to Twitter feed posts are boring and lazy in comparison to actual information post.

[Warpy]

14. 3 of us have now posted that story from 3 different sources

I guess more people than I thought were interested in this story.

The idea that the strength came solely from sea water never seemed like the whole story.

[Old Crank]

15. Two things

One is could this reduce the need for reinforcement in concrete? See earthquake regions.
Second, if yes, it saves energy and reduces the problems that reinforcing metsls bring to construction. The water can and will degrade the metal shortening the concretes lifespan.

[TeamProg]

18. Key info from link::

“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.

[cstanleytech]

19. I wish they would use it on the roads down in here in Georgia as the shit they

are using to patch the roads does not hold up and its rough to drive on.

[Wounded Bear]

20. Never too late to learn something new...

and what's old is new again.

[NullTuples]

21. Grady Hillhouse of 'Practical Engineering' YouTube channel fame has done videos on this.

"Meanwhile, many modern concrete structures have crumbled after a few decades."

Essentially it comes down to engineering decisions for modern concrete. Roman concrete had and still has many trade offs that modern engineers deem unacceptable. But also, we only see the Roman concrete works that have survived. There's evidence that much of what they built...did not survive long at all. Mostly because chemistry hadn't been invented yet and they were working by trial and error, unlike modern concrete engineers who can custom blend for specific needs such as setting time, tensile strength, resistance to cracking, etc. etc...

[bucolic_frolic]

22. They were all a bunch of cement heads /nt

[burrowowl]

23. Fascinating!

[WarGamer]

24. As a soils tech during college...

Sometimes we'd mic QuickLime into fill to increase compaction and density.

After it was mixed, layered and compacted you could walk over it and still fell the heat emanating.

[onethatcares]

28. I don't think we'll ever see this

discussed on that " ree public" place.

I love DU just for the learning.

[electric_blue68]

29. TY. That was really interesting!

[Kennah]

34. Here's to wagering capitalism will prevent this from ever happening

[summer_in_TX]

35. Exciting rediscovery!

Years ago I worked in a printing company publishing abstracts of UT College of Engineering research into concrete and asphalt. My job was to proofread these very technical abstracts. My main takeaway was that concrete started deteriorating at about 70 years. Now and then I think of that and worry about the concrete slab under our house. It's about 45 years old now so we have some time. I'd like it to last so our kids and grandkids can enjoy it.

Thanks for sharing that, Nevilledog!

[Ron Green]

36. Concrete has been, and is, one of the most harmful things to our planet.

The best policy would be to stop making and using it.

[mopinko]

37. this is my main beef w nukes.

they use sooooo much concrete and steal. lotta trash talk about the mining, etc of solar and wind, but…