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Why was Roman concrete so durable?

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Re: Why was Roman concrete so durable?

#211

Post by interfixus »

legitster wrote: post #2

Chemistry might be important, but we don't necessarily need that deep of an analysis. Romans didn't mind over-engineering with massive, inefficient structures. They didn't worry about complex/thin shapes, or any tensile elements. No rebar, no "piping" cement, etc. And they could put up with extremely long cure times. The end result is very, very dense concrete. We could probably recreate the durability of their concr…

> massive, inefficient structures

How does a building, an aqueduct, or a bridge still in use after 2000 years manage to be inefficient?

Re: Why was Roman concrete so durable?

#212

Post by urthor »

trynewideas wrote: post #57
urthor wrote: post #38

Earlier quoted context omitted.

Says a lot doesn't it. Marie Jackson makes it into the citations twelve times. Otherwise not mentioned by name. Academia: You thought capitalists were greedy for mere money? Come meet academics.

The lead author of this study, Linda M. Seymour, worked with Jackson on reference 29, on the mortar of the Tomb of Caecilia Metella, which is referenced repeatedly and the samples from which form a significant part of the hypothesis. That study: https://ceramics.onlinelibrary.wiley.com/doi/10.1111/jace.18... Story on that study: https://als.lbl.gov/unexpected-transformations-reinforce-rom... Jackson is quoted, if bri…

That's true, I'm not giving any credit at all to the fact the article isn't written by the paper's authors, and is at best a summary.

Re: Why was Roman concrete so durable?

#213

Post by Maursault »

akolbe wrote: post #103

Here is a nice picture of the Pantheon, mentioned in the article as a prime example of these incredibly durable Roman concrete structures: https://commons.wikimedia.org/wiki/File:Pantheon11111.jpg#/m... Not bad for something built nearly 2,000 years ago.

> Not bad for something built nearly 2,000 years ago.

According to the Pyramids, Stonehenge, Newgrange, Watson Brake, et al., it's a little premature to suggest that. Let's check back in 3,000 years.

Re: Why was Roman concrete so durable?

#214

Post by sph »

knodi123 wrote: post #128
legitster wrote: post #2

Chemistry might be important, but we don't necessarily need that deep of an analysis. Romans didn't mind over-engineering with massive, inefficient structures. They didn't worry about complex/thin shapes, or any tensile elements. No rebar, no "piping" cement, etc. And they could put up with extremely long cure times. The end result is very, very dense concrete. We could probably recreate the durability of their concr…

"Anyone can create a bridge that will hold up under a maximum load. It takes a real engineer to create a bridge that barely holds up under a maximum load."

It takes an accountant with a tight budget, you mean. Engineers will tend to make the most durable thing ever, if given enough time and money.

Re: Why was Roman concrete so durable?

#215

Post by [deleted] »

ricardobeat wrote: post #124
avereveard wrote: post #120

sea water + quicklime was known to be the "secret" for concrete for a while, this is a 2017 article https://www.washingtonpost.com/news/speaking-of-science/wp/2... can we put this to rest already?

If you pay attention to the article, the previous theory of seawater + volcanic ash turns out to not be the main reason for it's durability. The lime clasts being a feature, not a bug, and hot mixing, are the new discoveries.

[deleted]

Re: Why was Roman concrete so durable?

#216

Post by sporkland »

dima_vm wrote: post #162
LegitShady wrote: post #154

Earlier quoted context omitted.

this isn't really possible. For the rebar to take up meaningful tensile stresses, the concrete nearby must have cracked. Reinforced concrete ALWAYS cracks. If you want better corrosion resistance, you do other things - lower water ratios, increased concrete cover, sulfate resistant concrete with lower permeability, different reinforcing or epoxy coated reinforcing, etc.

Not always, if rebars are pre-tensioned before concrete solidifies. So the rebar is always under tension. Pretty common in prefab parts, like bridge bars.

For someone totally outside this space I had assumed concrete is rigid and brittle and rebar reinforcement allows for it to bend and flex without breaking. But your comment makes it feel like it keeps the concrete in tension with compression forces to make it sturdier. Can you ELI5 what the rebar does to help?

Re: Why was Roman concrete so durable?

#218

Post by _0w8t »

gerdesj wrote: post #126
legitster wrote: post #2

Chemistry might be important, but we don't necessarily need that deep of an analysis. Romans didn't mind over-engineering with massive, inefficient structures. They didn't worry about complex/thin shapes, or any tensile elements. No rebar, no "piping" cement, etc. And they could put up with extremely long cure times. The end result is very, very dense concrete. We could probably recreate the durability of their concr…

"Chemistry might be important" Conc is nearly all about chemistry. You mention curing rather than drying so you surely have some idea about what is going on. The Romans did not have electron microscopes so could not watch the way the matrix develops around the aggregate etc etc from the get go. To be fair, I fried my first sample in the beam at college by over focussing. They didn't use rebar because they generally b…

In Ancient Rome blaming gods was never an excuse. For example, there an architect or a chief builder had to spent several nights under the bridge after its opening. In general they followed a rule similar to one in ancient Babylon which explicitly required to put the architect to dearth if a building collapse would kill the owner. And if the collapse would kill a son of the owner, then the son of the architect would be put to death.

That puts rather different perspective on the quality and longevity.

Re: Why was Roman concrete so durable?

#219

Post by NineStarPoint »

ricardobeat wrote: post #127
dreen wrote: post #123

Earlier quoted context omitted.

I don't think the knowledge is gone, we could make that or maybe even better. The point is nobody wants it, most things we build need to be torn down after at most a few decades anyway.

The knowledge is actually gone, like Damascus Steel (what we have today is just a visual reproduction) and Greek Fire. For a more recent example: we already "forgot" how to make the spaceships and rockets that went to the moon. Even if you had the full plans - and apparently we don't, a lot of the materials and processes are not around anymore and would have to be 'reinvented'.

For the spaceship example, I’m fairly certain that we do know the theory behind how all those materials and processes are created though. It isn’t that we lost the knowledge, but the infrastructure. Recreating the infrastructure to create the materials to create the rockets is possible, it’s just that recreating entire processes from scratch when they had already been phased out of our modern structures would be outrageously expensive, especially just to construct rockets.

Re: Why was Roman concrete so durable?

#220

Post by Jensson »

amelius wrote: post #182
nimbius wrote: post #47

on the other end of the spectrum, did you know concrete can be used to demolish concrete? dexpan is a special demolition concrete mix that, when poured into holes, expands at 18kpsi. it gets used when jackhammers and explosives cant be used, for example, in refineries and explosive atmospheres.

Won't it expand out of the holes you poured it into?

Not if it hardens before it expands.
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