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Why was Roman concrete so durable?
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Re: Why was Roman concrete so durable?
#122sea 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?
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Re: Why was Roman concrete so durable?
#123> following all of the detailed recipes that had been optimized over the course of many centuries i wonder how all those detailed recipes were passed around for many centuries and now all is gone. Was it all passed down verbally?
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.
Re: Why was Roman concrete so durable?
#124sea 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.
Re: Why was Roman concrete so durable?
#125Earlier quoted context omitted.
for slow neighborhood roads I see no reason why brick isn't used more often. my hometown had brick roads everywhere and once every 3-5 years a few bricks would get replaced here and there. in the 1990s I'd look around and see a lot of the bricks on those roads that were made in the 1930s, and there were probably older bricks to be found if I'd looked harder. the rough ride kept speeding down a lot more than the polic…
Speaking as someone who grew up in a neighborhood with brick streets,... They're insanely slippery when wet. A freeze-thaw cycle tends to make them move, eventually leading to weird dips and ridges. They're expensive to install and more expensive to maintain.
they were not slippery that I noticed in my town. not sure why.
my town used dirt as the "mortar" between bricks, so there was no solid joint to degrade over time. I do remember crews going around and spreading small amounts of dirt on those roads, to refill what little rinsed away after spring thaw. they'd just have a guy following behind the truck with a push broom moving the dirt so it fell between bricks.
dirt is dirt cheap.
Re: Why was Roman concrete so durable?
#126Chemistry 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 built in compression - arches etc. Rebar and pre-stressing enables members to cope much better under tension. A PS beam or slab is a modern marvel and even protects the steel from fire - bonus.
Cure times: weather/environment. In hot climes you need to stop the water buggering off the surface and leaving cracked and spalling surfaces before it even cures. It may also over heat (exothermic reaction). Cold - slower curing, too cold - no cure and frozen water (total disaster). Underwater - watch your fines wandering off and going for a smoke behind a reef and your structure collapsing, unless you keep them in place.
Concrete curing is not like smoking a joint of meat! A quick or slow cure may be indicated depending on conditions. We have admixtures and all sorts to fiddle with parameters. Then you have things like grading and composing your agg. and other exciting stuff.
I could go on at some length - it is really, really complicated. Roman engineers managed to invent an ancient wonder of chemistry and physics that was concrete. Their approach to its use and improvements was obviously rather better than what passed for science and medicine at the time! They do seem to have experimented and gone with what worked best but it was never deliberately developed from first principles. The self healing thing was probably a happy accident.
A Roman engineer had some rather different design constraints than a modern Civil. For starters, failure could quite legitimately be blamed on the god's displeasure. "When that bridge was commissioned, we made all the correct sacrifices and anyway, you are holding it wrong, I mean walking on it incorrectly".
(sp)
Re: Why was Roman concrete so durable?
#127> following all of the detailed recipes that had been optimized over the course of many centuries i wonder how all those detailed recipes were passed around for many centuries and now all is gone. Was it all passed down verbally?
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'.
Re: Why was Roman concrete so durable?
#128Chemistry 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."
Re: Why was Roman concrete so durable?
#129Isn'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)?
Re: Why was Roman concrete so durable?
#130the 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…
I agree with the spirit of what you're saying but you go too far, ironically asserting without any supporting logic that the intelligence of homo sapiens has remained static for the last 2,000 years. But I suppose the disagreement hinges on what is meant by intelligence. Here's a thought experiment: if you removed all technology (tools, writing, vast stores of knowledge) from a human child and raised them in this vac…
"intelligence," as I used it, is the ability to learn, to use what you've learned to solve problems, and to accurately predict the future outcomes of today's decisions.
my knowledge of the horsehead nebula has no positive or negative effect on my ability to learn how to make concrete or to use that knowledge to actually make thae concrete. intelligence is not simple memorization of fact, it is a collection of understanding, and the ability to both grow that understanding and to use it to accomplish things that you don't yet know how to do.
we are continuously surprised by what we learn about ancient cultures, because we assume they were intellectually inferior to us.
the Lycurgus Cup is a great example of something that some people still view as a lucky accident. Anyone who has actually learned to make physical things and worked to refine their skill in making things will know in their soul that the colors in that cup are clearly intentional and the product of intelligence and time.
our belief that only contemporary humans have control over and understanding of the their world is just simply wrong, I think.
we discover new evidence from ancient civilizations which surprise us all the time. is there enough evidence to prove that we aren't smarter than people 100-200 generations ago? I don't know.
there certainly is a lot of evidence that ancient civilizations knew more than we believe they knew, and that is significant when you think about how long that evidence needs to last to be discovered today, and that those things which do last long enough are recognized for what they are before they are discarded because of a bad assumption. how much evidence has been lost? we only see a tiny fraction of the evidence that would have existed at the time.
these discoveries happen frequently enough for me to have no problem believing that there is a great deal about ancient civilizations that we think we know which we actually do not know.
that's a rambly comment but it's all I have time for before the edit window closes.