A 1700-yr old mystery possibly solved!

[edward bloom]

sometimes, it can come down to how you apply something. it's one of the reasons i love the dome. the system he used to lay out the shape is true-length. something i use in pattern layout all the time. it's something you learn as a first year sheetmetal worker. he drew a pattern on the ground, and ran strings from key points on the pattern to ensure the measurements remained precise. it took people almost 400 years to figure out that he did that.

there were of course many other things he did that were brilliant, but also simple. he just applied them in a way no one thought of before him. except for the reversible hoist thing, all of it was stuff people had done before, but hadn't used it the way he did. they built the cathedral but had wait 120 years for someone to come along who could put the dome on it. the guy was a genius, and he knew it. he seemed to have no hesitation for making other people aware of it too. hahaha

 

[Old Fart]

... he used to ...

Who?

BTW, I've got high respect for sheet metal workers. I had to join a union as part of my job, very briefly, and I chose SMW. I think you guys are the green berets of the trades.

 

[MoireBass]

It is amusing to me, the impressive contingent of people who will believe something exciting, something romantic, something intriguing largely because it is so unlikely and counterintuitive, just on the basis of a suggested theory which flies in the face of facts and logic.

Why did you jump to the assumption that this was an internet rumor and we were all chickens chasing a plastic worm?

I first learned about the durability of Roman concrete in 2009 and have followed research on it as it's been released since then. NOVA, the PBS science show, had a good episode on Roman concrete 5 or 6 years ago. NOVA is where the figure of 60 years in the sea and the example of the north African jetty came from.

It is not imaginary that Roman concrete is stronger and more durable than modern concrete, researchers can break pieces and compare it to modern concrete examples of any age. Testing Roman concrete isn't like cutting off a corner of the Shroud of Turin, there are hundreds of tons of it laying around available for research. This isn't speculation or empty assertion, they have actual real-world measurements showing the superior strength. People have spent millions of dollars and years of their life trying to figure out why, starting before the internet was invented.

My interest stems from the fact that I worked as a form-setter/concrete-finisher/journeyman-carpenter for about two years to finance school. I poured miles, literally miles, of concrete. Found out then that concrete is really a very complex material that acts in odd and unexpected ways.

I guess what I am bristling at is the perception that modern concrete is inferior, or at least inferior to Roman concrete, and I'm not convinced of that. Not even if I read it on the Interwebs.

Bristle all you like, but facts is facts.

 

[MoireBass]

many still trapped under concrete. Many lives lost. Some of our engineers will be girding their loins, right about now. Some will be going back to the drawing-board. Concrete, in some of its guises, may not be all it's cracked up to be.

One of the puzzling features of Roman concrete is how well it stands up to earthquakes. People have noticed for centuries that earthquakes would destroy modern structures while ancient Roman ones survive.

 

[Tom Bomb]

My question then would be, yeah, but what have the Romans ever done for us?
​

 

[MoireBass]

My question then would be, yeah, but what have the Romans ever done for us?​

Yeah! Apart from the aquaduct, sanitation, sewers, roads, irrigation, medicine, education, wine, public baths, public safety, public health, and world peace, NOTHING AT ALL!

Best scene in what has been voted the funniest movie ever made. Thank you, George Harrison!
{OK, the guys who are being crucified whistling 'Always Look On The Sunny Side of Life' is a pretty close second.}

 

[Tom Bomb]

Those bloody Romans pert near did me in. I don't think I've ever laughed so hard.​

 

[Old Fart]

Yeah! Apart from the aquaduct, sanitation, sewers, roads, irrigation, medicine, education, wine, public baths, public safety, public health, and world peace, NOTHING AT ALL!

THe Romans, and more accurately the Greeks, pioneered these sciences. And they did an astonishing job. Today, we are studying properties of their concrete mixes to better understand their surprising longevity. And other curiosities of antiquity.

But if anyone wants to imagine the Romans knew more about water, sanitation, road, and public safety systems, or that they knew more about medicine, concrete, wine or public health (should we throw astronomy here as well?) than scientists do today, then I invite you to go on thinking those things without any further argument from me. Plus, it's fun to think that MIT and you guys are out-thinking the world's engineers, researchers and doctors.

Roads. There is another kettle of fish. Again, I am not going to argue further. Except to say today's engineers do know how to build a nearly-forever "road prism" (the road's foundation). They just don't do it. They want freeway prisms to last hundreds of years, not thousands. If they wanted to, they could.

 

[MoireBass]

to go on thinking those things without any further argument from me. Plus, it's fun to think that MIT and you guys are out-thinking the world's engineers, researchers and doctors.

MIT stands for Massachusetts Institute of Technology, one of the world's best engineering schools. It is famed for the quality of its research. The people who are doing this research are engineers with a Master's degree who are working on their Ph.D.s in engineering.

 

[gln1955]

I appreciate that and I don't believe MIT is lying, but I do suspect their findings may have been sensationalized and/or mischaracterized. Roman concrete is being analyzed to find improvements in our processes. Granted. I see their findings about some material eroding away but then being replaced by a crystaline structure that improves hardness. Alright.

But the Colosseum is falling apart right now and we've got a 250+ year old lighthouse sitting in the water than looks brand new. I visited a hydroelectric turbine enclosure (the concrete room in which the turbine impeller is turned by moving water) a couple of decades ago and hear the engineers report that the wear on that concrete surface was less than a half-inch. About a half-century in age. They grinned proudly when they said it, and rightly so. Water at hard-to-imagine pressures and velocities, rushes across that concrete surface almost continuously.

I guess what I am bristling at is the perception that modern concrete is inferior, or at least inferior to Roman concrete, and I'm not convinced of that. Not even if I read it on the Interwebs.

Did you read the research article? Not the blurb, but the paper linked from it with all of the rationale, data and conclusions.

Please tell us were they went wrong.

 

[edward bloom]

Who?

BTW, I've got high respect for sheet metal workers. I had to join a union as part of my job, very briefly, and I chose SMW. I think you guys are the green berets of the trades.

his name is phillipo bruneleschi, and he's one of my all time favorite characters from history. he built the dome on the cathedral in florence italy. the video below will give you the cliff notes of why both he, and the dome are so cool, as well as how it ties in with roman concrete and building techniques. however, there is much more cool stuff to that story than what is contained in a 13 minute video



it's nice to hear your appreciation for tin knockers. like all tradesmen, we work hard, and try to do our best. we don't get to hear that sort of stuff very often. heck, even ronald reagan gave all of our glory to the iron workers when we refurbished the statue of liberty. hahahaha (trivia: lou ferigno, the incredible hulk, was a sheetmetal worker in new york)

 

[bholder]

OK, cool, now find me the recipe for Valerian steel, please?

 

[HaphAsSard]

But if anyone wants to imagine the Romans knew more about water, sanitation, road, and public safety systems, or that they knew more about medicine, concrete, wine or public health (should we throw astronomy here as well?)

More to the point, why are you imagining up strawmen?

Did you read the research article? Not the blurb, but the paper linked from it with all of the rationale, data and conclusions.

Please tell us were they went wrong.

^ This. Retrieve the research paper, so that you can't blame the credulity of journalism students, or ours; then zero in on what is actually claimed, by the researchers, about Roman concrete vs. modern technology.

 

[hrodbert696]

The Colisseum almost no longer exists. Half of it is GONE and the other half is only standing because of structural repairs and improvements.

Ummm... the condition of the Colosseum has nothing to do with the quality of its concrete. Actually, it's a testament to how durable Roman concrete was and is. A succession of Christian emperors in the 4th and 5th centuries issued decrees curtailing or forbidding gladiatorial matches. As with any legislation, the effect wasn't immediate and complete around the entire empire, but over that time the ludi (games) did indeed peter out and the Colosseum sat empty.

In the sixth through eighth centuries, Rome suffered general depopulation - it wasn't a functioning imperial capital anymore, that was at Constantinople, so there was little reason for people to flock there from the countryside. The Forum with all its temples sat unused as the remaining population, now largely Christian, clustered around other centers like the Vatican or the Lateran. The other thing was that there was twenty years of warfare - the Gothic Wars - in which the city was besieged and changed hands four times, meaning a constant need to repair defensive walls that were always being damaged or rebuild houses that had been damaged each time the city was sacked. Lombard invasions followed, from 568 onward.

Those centuries were also the period when church authorities came to dominate the city, increasingly taking over governing functions from secular officials. As the pope and other clergy rose in prominence and power, they built new churches and expanded existing ones. Eventually in the 700s Charlemagne recognized Rome (and a swath of central Italy) as the "Patrimony of St. Peter," or what would later be called the Papal State.

The point of this is that you had several centuries in the Early Middle Ages (and later) when there was a lot of demand in Rome for building material, to reinforce defensive walls and to build and expand churches, AND when you had a gigantic pile of ready-made durable material right at hand, sitting unused, that you wouldn't have to quarry raw and drag down from the mountains. Half the Colosseum is gone, not because it crumbled away under the elements, but because it went into Rome's churches and walls and bridges and street pavements. The phenomenon is called "spolia" and it's very well-documented by archeologists and historians, who are frequently finding some slab of stone or concrete with a valuable historical inscription or relief carving on it, dumped face-down to help a farmer cross a brook or embedded in a monastery wall or something.

 

[hrodbert696]

I'll also comment, here a little further off my field of expertise - I think someone had mentioned that the concrete-making process the Romans would use would set pretty quickly, so you couldn't afford building delays. In a completely other context I recall hearing of a major building project in New York that went up remarkably fast by using a quick-setting concrete. It wasn't the usual material to use because any kind of union pushback like a strike or work slowdown could nix an entire project using it, and the choice of this material in this particular building raised suspicions of mob involvement to keep the unions compliant. With Roman slave labor, presumably that wouldn't have been a concern. So sometimes with these kinds of things, it isn't so much that modern technology doesn't know how to make something equivalent to what the Romans did, but that social or economic contexts make it impractical to do it the way that they did.

 

[RichterScale]

Exactly. There's a TV show called "if we built it today", or something like that.
One of the major factors they estimate for building something today is cost.
Part of cost is labor.
These weren't necessarily factored the same way, or factors at all 2- 20k yrs ago.
Also, other factors were different. Like, how culture and communities were structured, motivation for building, etc.
They didn't hire a profit based construction company to build the pyramids.

 

[hrodbert696]

They didn't hire a profit based construction company to build the pyramids.

Fun fact - apparently, building the pyramids in ancient Egypt was a way to pay your taxes. The Pharaohs required a share of people's working hours each year, not cash.

 

[Rich Fiscus]

It is certainly sensational to imagine that today's engineers don't know as much as Romans did 2000 years ago, but that is not true. Not by any stretch. It does not even pass the "straight face test."

No it doesn’t. Not surprisingly, that’s not what Invalid Link Removed says either. Here’s the abstract.

Ancient Roman concretes have survived millennia, but mechanistic insights into their durability remain an enigma. Here, we use a multiscale correlative elemental and chemical mapping approach to investigating relict lime clasts, a ubiquitous and conspicuous mineral component associated with ancient Roman mortars. Together, these analyses provide new insights into mortar preparation methodologies and provide evidence that the Romans employed hot mixing, using quicklime in conjunction with, or instead of, slaked lime, to create an environment where high surface area aggregate-scale lime clasts are retained within the mortar matrix. Inspired by these findings, we propose that these macroscopic inclusions might serve as critical sources of reactive calcium for long-term pore and crack-filling or post-pozzolanic reactivity within the cementitious constructs. The subsequent development and testing of modern lime clast–containing cementitious mixtures demonstrate their self-healing potential, thus paving the way for the development of more durable, resilient, and sustainable concrete formulations.

As far as Roman concrete being superior to modern formulations, that’s more than a stretch. For starters, its longevity is at least partly due to insanely long curing time - as in decades vs weeks for modern concrete. It has lower plasticity, which the Romans certainly didn’t understand the importance of, and is generally a bit weaker, even after it “finishes” curing.

They definitely stumbled across polazzo for resisting saltwater, which made it ideal for use underwater. However, there’s no indication they knew why it worked, or that the salt in the water was part of the equation. We know all of that today.

As with all the recent research into Roman concrete in the last decade or so, the purpose of this study was to reverse engineer the final product, not to learn what the Romans knew, but simply to understand how to duplicate particular properties the Romans stumbled across, and integrate it into modern concrete engineering.

 

[HaphAsSard]

I'll also comment, here a little further off my field of expertise - I think someone had mentioned that the concrete-making process the Romans would use would set pretty quickly, so you couldn't afford building delays. In a completely other context I recall hearing of a major building project in New York that went up remarkably fast by using a quick-setting concrete. It wasn't the usual material to use because any kind of union pushback like a strike or work slowdown could nix an entire project using it, and the choice of this material in this particular building raised suspicions of mob involvement to keep the unions compliant. With Roman slave labor, presumably that wouldn't have been a concern. So sometimes with these kinds of things, it isn't so much that modern technology doesn't know how to make something equivalent to what the Romans did, but that social or economic contexts make it impractical to do it the way that they did.

Huh. Of all the contrived ways to bring discussion to slave labour each and every time the Romans get mentioned, this was one of them.
Unless, as suggested - not in earnest I would guess - by a poster above, actual bones of slaves can be proven to be an essential ingredient of Roman concrete, your example is hardly germane to the topic at hand. If anything, you proved the Roman way can be replicated: a little Hoffa goes a long way to give a building solid foundations.
(In more ways than one, amirite?
What? Too soon?)
What about less-unionised countries? While I think workers' strikes did occur during the construction of Qatar football arenas, was it significantly hindered by them? If it wasn't, will this mean anything in terms of durability of the structures? Do engineers expect Shanghai skyscrapers to last longer because of how authorities can better control the workers that made them?
I suppose I could lead with saying I'm no expert, then proceed to suggest that the beauty of Mediterranean vistas may well have crucially inspired ancient master craftsmen in devising ways to make their concrete mix durable for the ages. Hey, it could be, couldn't it?

 

[Old Fart]

Did you read the research article?

Yes, I did.

Please tell us were they went wrong.

Not again, I won't.

.... phillipo bruneleschi (who) built the dome on the cathedral in florence italy......

it's nice to hear your appreciation for tin knockers.

Ha! I will be spending a few days in Florence in late April and I totally will be visiting the Duomo, and its museum!

Some of the stainless fab work you guys do is breathtaking. Truly art. And like Roman concrete to the MIT guys, at times I have looked at work done by your craft and wondered "How did he even do that?"

I'll also comment, here a little further off my field of expertise - I think someone had mentioned that the concrete-making process the Romans would use would set pretty quickly, so you couldn't afford building delays. In a completely other context I recall hearing of a major building project in New York that went up remarkably fast by using a quick-setting concrete. It wasn't the usual material to use because any kind of union pushback like a strike or work slowdown could nix an entire project using it, and the choice of this material in this particular building raised suspicions of mob involvement to keep the unions compliant. With Roman slave labor, presumably that wouldn't have been a concern. So sometimes with these kinds of things, it isn't so much that modern technology doesn't know how to make something equivalent to what the Romans did, but that social or economic contexts make it impractical to do it the way that they did.

On the topic of how hot the mix is and how quickly it cures, see below.

I participated in the construction of an international airport runway 200' wide and nearly a mile long. We batched the concrete on site. My role was labor relations. There was no strike, nor would there have been. Long story, but there was no "mob" connection. Only the union local business managers at the general presidents themselves.

The concrete got to the slip form paver in dump trucks and it set up immediately. Runways can actually land planes pretty much as soon as the concrete is placed. The mix is hot. But the surface requires more preparation. For example, longitudinal grooves are cut into it. For traction and weather reasons.

Rich has good reading comprehension and writing skills:

No it doesn’t. Not surprisingly, that’s not what Invalid Link Removed says either. Here’s the abstract.

As far as Roman concrete being superior to modern formulations, that’s more than a stretch. For starters, its longevity is at least partly due to insanely long curing time - as in decades vs weeks for modern concrete. It has lower plasticity, which the Romans certainly didn’t understand the importance of, and is generally a bit weaker, even after it “finishes” curing.

They definitely stumbled across polazzo for resisting saltwater, which made it ideal for use underwater. However, there’s no indication they knew why it worked, or that the salt in the water was part of the equation. We know all of that today.

As with all the recent research into Roman concrete in the last decade or so, the purpose of this study was to reverse engineer the final product, not to learn what the Romans knew, but simply to understand how to duplicate particular properties the Romans stumbled across, and integrate it into modern concrete engineering.

But now....these last two quotes seem to conflict. One suggest Romans used hot mixes and the other suggests long-set mixes. I suspect the latter is more true. For several reasons, including the handling requirements of hot mixes. Some mixes are so hot that they set up in minutes. When the water is added, the concrete must be placed NOW. A cubic yard of concrete weighs about two tons. They did not have our knowledge OR our heavy equipment.

And as I say, I'm not going to repeat what I already said except for this: Concrete....all concrete....continues curing for decades. It is stronger at sixty years of age than it was at twenty. Technically, concrete never stops curing. But it does "set" enough for practical use in about "X" period of time. "X" might be a week or month, but it can also be a half-hour or even less.