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Why was Roman concrete so durable?

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Re: Why was Roman concrete so durable?

#181

Post by dreen »

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'.

I was referring to the knowledge of how to make long lasting concrete, not necessarily specifically how the Romans did it, but I guess I could've been clearer.

Re: Why was Roman concrete so durable?

#182

Post by amelius »

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?

Re: Why was Roman concrete so durable?

#183

Post by ShredKazoo »

>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.

So this method wouldn't necessarily work in a dry climate without much rain?

Re: Why was Roman concrete so durable?

#184

Post by Spooky23 »

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…

I worked on a campus where they were building a building that had to be incredibly stable - they had to coordinate arrivals of like 30 trucks making 4-5 trips a day. Each truck had like 180 seconds to unload.

Because of the coordination requirements, they embedded sensors in the structure and adjusted the water for curing and would slow down or speed up the flow of trucks based on how the process went.

One of the engineers told me that a thousand years from now, someone would wonder why this slab is here. I’m sure he was mostly kidding, but it seemed believable.

Re: Why was Roman concrete so durable?

#185

Post by sarchertech »

HPsquared wrote: post #45
sarchertech wrote: post #17

Earlier quoted context omitted.

That depends on the what you mean by smarter. At least some component of what we consider intelligence is cultural. Just one example is that the ability to write/draw allows you to solve problems that are impossible without it.

Being literate definitely means some faculties get less practice. Practically nobody today can recite epic poetry like the Odyssey, for example. That lack of rote memorization skill may have unexpected side-effects. https://daily.jstor.org/how-do-we-know-that-epic-poems-were-...

That’s possible, but unlikely considering that numerous studies of literate vs illiterate people have shown that literacy correlates with improved working memory not the inverse.

Studies of using mnemonic techniques to memorize long sequences (similar to what oral performers were doing) have also not shown much promise in increasing cognitive abilities.

Re: Why was Roman concrete so durable?

#186

Post by zoklet-enjoyer »

moloch-hai wrote: post #177
LegitShady wrote: post #157

Earlier quoted context omitted.

> The rust is essential to bind it to the cement. Without, it adds little strength. Do you have a citation for this? As far as I know this is entirely not true. Rust is an expansionary product - when steel rusts its volume increases something like 10x, which reduces the connection between the concrete and the steel and causes issues like cracking and spalling. Minimizing rust improves the long term performance of reb…

They leave the rebar out to rust a bit, on purpose, before they pour. Surface rust is good, but more is bad. Like many things in life.

I read your comment as I finished eating my third slice of pie and wondering why I cut myself 3 slices.

Re: Why was Roman concrete so durable?

#187

Post by chrisdhoover »

moloch-hai wrote: post #144
masklinn wrote: post #134

Earlier quoted context omitted.

> as well as expanding rust. Ideally they’d seal before the rebar is exposed and can rust. As long as the rebar is encased, unless you fucked up dramatically it should be safe.

The rust is essential to bind it to the cement. Without, it adds little strength. Modern concrete isn't expected or designed to last more than a century. It could have been made to last longer, if they wanted, but that would cost a little more. Making no provision for when it will predictably fall apart is a modern failing. That major construction with concrete is about a century old should worry everyone. We have a…

So the Hoover dam will fail in 10 years?

Re: Why was Roman concrete so durable?

#188

Post by tuatoru »

oakwhiz wrote: post #132
boogoob wrote: post #129

Isn't the particularly short lifespan of modern concrete construction mostly a combination of its use in areas with regular freeze-thaw cycles and using a reinforcement material that rusts (and in doing so expands, damaging more concrete and hastening further water inclusion)?

The rusting and getting wet is cyclical in nature and part of what accelerates that is the formation of cracks in the first place. Part of the maintenance of concrete is to fill any cracks that you can find to prevent it from getting worse. The cracks typically start small, and they might form in places that are hard to get to as well as being too small to see, so if the concrete is self-healing it will prevent some…

> expanding rust

The alkaline environment inside concrete "passivates" the reinforcing bar, greatly reducing the rate of oxidation and changing its form.

The problem exists only in concrete that is badly made with poorly chosen aggregate, and in corrosive environments.

1. https://en.wikipedia.org/wiki/Passivation_(chemistry)

Re: Why was Roman concrete so durable?

#189

Post by tuatoru »

boogoob wrote: post #129

Isn't the particularly short lifespan of modern concrete construction mostly a combination of its use in areas with regular freeze-thaw cycles and using a reinforcement material that rusts (and in doing so expands, damaging more concrete and hastening further water inclusion)?

> Isn't the particularly short lifespan of modern concrete construction mostly a combination of its use in areas with regular freeze-thaw cycles and using a reinforcement material that rusts

No. It's a consequence of designing to requirements of minimum cost and a 50-year lifespan. It'd be easy to make concrete with much longer lifespan, but it costs more.

Re: Why was Roman concrete so durable?

#190

Post by PakG1 »

zoklet-enjoyer wrote: post #186
moloch-hai wrote: post #177

Earlier quoted context omitted.

They leave the rebar out to rust a bit, on purpose, before they pour. Surface rust is good, but more is bad. Like many things in life.

I read your comment as I finished eating my third slice of pie and wondering why I cut myself 3 slices.

3 is the limit. More than 3 is bad.
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