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Why was Roman concrete so durable?

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191–200 of 299 posts

Re: Why was Roman concrete so durable?

#191

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.

It's a nice thought that all these depressive brutalistic/modernist builduings will all soon crumbly by the same mechanism that spawned them!

Re: Why was Roman concrete so durable?

#192

Earlier quoted context omitted.

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?

Fortunately, Hoover Dam is under compressive load.

Re: Why was Roman concrete so durable?

#193

Earlier quoted context omitted.

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?

Only if the Hoover dam was made with standard concrete using standard building methods, I suppose.

Re: Why was Roman concrete so durable?

#194
post #81

For people who don't know the difference between cement, mortar and concrete: Cement is a substance used for producing mortar and concrete. It's never used on its own. It is a "binding agent". Note that the term "cement" is often not used correctly in everyday speech, with people talking about gluing bricks together with cement, when bricks are actually glued together with mortar. Mortar is the glue between bricks. Y…

Well, technically, you can use cement instead of mortar (wet, but without sand). As far as I understand, sand is more like a neutral filler, to save money on cement. Various other things can be used to fill as well, like gravel. Sometimes even empty plastic bottles (reduces material and weight) are suitable (just make sure they don't float up). If one got very smooth bricks (e.g. precisely cut aerated concrete), then…

If the sand is properly coarse, it can add strength. However, finding coarse sand is increasingly difficult, resulting in misuse of smooth sand (from error or being defrauded).

Tangent: coarse sand is also important for certain types of septic systems to function properly.

Re: Why was Roman concrete so durable?

#195

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.

Perhaps you’re just mathematically inclined.

Re: Why was Roman concrete so durable?

#196
post #181

Earlier quoted context omitted.

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.

The answer is still no, we don't know how to make long lasting concrete with modern techniques either apparently. Hence the research.

Especially steel-reinforced concrete, the lifespan is only 50-100 years. The only exceptions are massive structures like dams that will probably last a couple millennia.

Re: Why was Roman concrete so durable?

#197

Earlier quoted context omitted.

> 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.

It's a nice thought that all these depressive brutalistic/modernist builduings will all soon crumbly by the same mechanism that spawned them!

Most brutalist buildings are already 60+ ish years old and doing great (actual brutalism, rather than “concrete buildings I don’t like,” was mostly a style of the 1950s and 60s in the west, though it lasted quite a bit longer in Eastern Europe). Even the Boston government services center, everyone’s most hated brutalist building in the US is already past 50.

Re: Why was Roman concrete so durable?

#198

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…

> The rust is essential to bind it to the cement

What? This is total nonsense.

> 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.

Is hacker news a conspiracy theory website now?

> We have a very great deal of infrastructure that will fail on a predictable schedule

Wood rots in a few years under certain conditions and can last hundreds in others. Concrete works similarly.

The 3rd pantheon is currently standing, but it is a huge mix of repairs across centuries. The Romans built many structures that are similar but now are in ruins because the Catholics didn’t maintain the roofs on bathhouses.

Re: Why was Roman concrete so durable?

#200
post #60

the article talks about evidence which has always been present in evaluations of Roman concrete which was "disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials," and this kind of thing REALLY infuriates me, as a layman. if you don't know how to make Roman concrete, don't assume anything about what you see in Roman concrete while you're trying to figure out how it was made. The mode…

> if you don't know how to make Roman concrete, don't assume anything That's not useful guidance for doing research at all. It's similar to some 19th-century physicists/philosophers saying 'if you can't see atoms, you can't possibly know anything about them or whether they even exist'. We also can't make supernovae or supermassive black holes, yet we can still try to learn about them through a combination of availabl…

eh, I disagree.

hypothesizing that atoms exist allows and encourages you to design experiments which can prove or disprove their existence.

assuming that they exist, and never experimentally verifying that is not research and it is not science.

assuming that some feature of a product that you do not understand exists for any reason is at most an hypothesis, and dismissing the hypothesis without experimental evidence disproving it is simply bad science.

Roman concrete is not something far away that we can not interact with. we can verify by experiment. for years we chose not to validate the assumption that the white specs were accidental, and that delayed our understanding of Roman concrete.

I just want scientists and historians that take the time to recognize their assumptions and to prove them correct or incorrect, if possible, instead of just relying on them as immutable facts; assumptions are often wrong.

I write software for a living, and the number of times that my assumptions about the cause of any particular problem have been correct approximately 0% of the time. whether it's a logic bug or a performance problem or a usability problem. despite decades of experience in this field, I am still almost always wrong about the cause of any particular problem I encounter, unless I have seen that exact same issue previously, which is rare.

historians, some of them at least, would probably benefit quite a bit from making fewer assumptions and by experimentally proving the assumptions they do make. if it isn't possible to prove or disprove your assumption, then you must never forget that it is an assumption and not proven fact.

I've seen so many scientists and historians say they know things which they simply do not know. things like "we know dark matter exists." no, we don't. we know that the currently accepted theories of our observations require dark matter to exist in order for our observations to make sense. that is not proof of dark matter.

dark matter may exist! I don't know, but for a scientist to say that it exists is incorrect because we've never observed it directly, and have devised no tests which can prove that it does exist.

our theories which require it in order for our observations to make sense could be wrong. our observations may not be as accurate as we assume. we may be observing things that we aren't aware of which look like something that we are aware of. etc.

I'm saying that professing that you know something without proof is folly. just like the white specs in the concrete were assumed to be accidental impurity without that hypothesis being proven is folly. these things set us back as a scientific community that wants to understand its environment.

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