Is that what I think it is?If they try to sell you one of these, don't buy it, dam it.
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A 1700-yr old mystery possibly solved!
- Thread starter MoireBass
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The concrete in Hoover Dam is still curing. Water is still being pumped through the structure for cooling. Concrete does not "dry," it "cures." A chemical reaction causes the hardening. Hoover Dam is still hot in the center.
Ancient mysteries are always fascinating aren't they?
Equally fascinating is how some are considered controversial subjects, especially the more that modern science can provide evidence. It's like their mere existence provokes fear and anger in people. They are afraid to shed light on the topic.
Oh well.
Equally fascinating is how some are considered controversial subjects, especially the more that modern science can provide evidence. It's like their mere existence provokes fear and anger in people. They are afraid to shed light on the topic.
Oh well.
when i saw this thread, that was basically what i came in here to say. you put it well.
i hope not.
california rice feeds millions of people. i've got almost 20 lbs of it in my pantry right now. ex #2 was japanese. she was picky about the rice we put on our table. it was always from california. her parents (in japan) would send us a big box of snacks every other month, along with a letter and maybe a photo or two. once a year, before christmas, they would include a small bag of rice that was locally grown near her parents. i guess they wanted her and the kids to have a "taste of home" during the holidays. it always made her sooo happy to eat it. to call the kids to dinner she would say "GO-HAAAN!!!" gohan means cooked rice. i didn't grow up with rice as a staple like she did, so to me, the difference was really subtle. come to think of it, i never told her that i couldn't tell much difference. i just said "oishi!!!" (delicious) and kept eating. but there you have it. california grows alot of rice, and it's really good. if we lost that, it would be a disaster
Sure, if this research proves to be correct, it'll still take a lot of development to make it practical for use on a worksite. If the ancient Romans could do it with slave labor and wood fires though, I'm sure modern engineers could design a machine to do it too.
Have you watched those concrete pumpers? They accept mix from a cement truck and pump it several hundred feet. Maybe something similar could mix in one ingredient and final-heat the mixture.
Good general life advice. But this write-up is about a research paper from the MIT labs. The MIT labs have produced a lot of very good research before and so I'll assume for the moment that they're not deliberately lying. It's easy for researchers to fool themselves though so, like most research, this means nothing until other people can replicate their results.
It is not new information that Roman concrete is much more durable than all our modern formulations or that builders have been trying to reproduce it for the last 1700 years though. This is widely known and documented.
That's cool. The last concrete I poured for a project designed by a civil engineer was 1982, so the epoxy-coated rebar is a development since then. Is it much more expensive than the regular? Probably so, the last time I bought rebar at Home Depot to pour some steps at my Dad's house, all they had was the same ol' same ol' uncoated rebar that we've been using for decades.
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This same lab at MIT is also working on concrete that absorbs greenhouse gasses from the air, and on concrete that is less environmentally damaging to produce. The present discovery involves microscopic sections of calcium-carbonate embedded within the concrete mixture that refill microscopic cracks when they occur. What if they could instead embed microbeads of calcium that absorbed carbon directly from the air to repair the concrete - and that concrete was significantly better for the environment than what we have today? Is that possible? No one knows yet.
Humans are NOT going to give up concrete because its production produces a lot of greenhouse gases. Concrete is just way too useful to us. Buckminster Fuller said something I really like: "You never change things by fighting against the existing reality. To change something, build a new model that makes the old model obsolete."
Sure, but there are also many applications such as building slabs, roads, etc. where it might be possible to eliminate or reduce the iron reinforcement. And production of iron is even worse for the environment than of cement.
Buck
i have seen some interesting stuff done with aerated concrete:
on the other hand, there are also some really ugly examples of what can happen when greed causes people to cut corners, like the sampoong mall collapse in korea:
there was a pretty cool drama made about this called "gaeulro" aka "traces of love" if you don't mind subtitles,(assuming you don't speak korean) it's probably available to watch online somewhere. kind of a freaky story
on the other hand, there are also some really ugly examples of what can happen when greed causes people to cut corners, like the sampoong mall collapse in korea:
there was a pretty cool drama made about this called "gaeulro" aka "traces of love" if you don't mind subtitles,(assuming you don't speak korean) it's probably available to watch online somewhere. kind of a freaky story
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.
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.
what concrete structures do we have that will ever be 2,000 years old? by the calculations of the turbine enclosure you mentioned, assuming the erosion was linear (almost never) it would have eroded almost 2'. it's not going to survive that kind of erosion.
the lighthouse you mentioned is only a tenth the age of the coloseum. it might look great now, but 1800 years in the future? the pyramids and ziggurats and monoliths all over the world were already ancient when Christ walked the earth. i don't know of anything we've built that will be as enduring as they. we have done some cool stuff, no argument there. however, it's obvious there was knowledge available in the past we no longer have. even bruneleschi fooled the world for what? 400 years i think?
Concrete may crumble. Culture sometimes builds longer lasting things. Sometimes you have to dig for them. Sometimes you'll find material all ground up and added to the mortar of older brick dwellings. Many of these old buildings still stand. Having them protected, by bodies like the National Trust, plays a critical role.
'The oldest known Aboriginal shell midden place on the Victorian coast is nearly 12,000 years old. At this time sea levels were lower because icecaps at the north and south poles were much larger than today. … Shell middens which contain burials are particularly significant.'
Aboriginal coastal shell middens
Aboriginal coastal shell middens
Really? It is amusing to me, on this topic and so many others, 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. The Colisseum almost no longer exists. Half of it is GONE and the other half is only standing because of structural repairs and improvements.
The question of how long modern concrete structures will last, and there has been nowhere near enough time to even guess at that. And it will be challenging to answer even when time has run its course. Why? Because we don't leave structures standing until they fall on their own. We demolish them for purposes of public safety and, more often, because new technologies have given us the ability to replace them with better, more functional structures. The Empire State Building is still structurally sound, but is only still standing because it is such an iconic landmark. it was not designed to accommodate modern air-handling, safety and electrical/technological systems.
Some years ago, the out-dated Kingdome was demolished near me. It was out-dated, and was replaced by two EXCELLENT sports stadiums. Maybe the best baseball stadium in the nation. But left alone who knows how long the Kingdome would have stood. Its implosion required a massive amount of explosives. It was built like the proverbial brick outhouse. Personally, I think it would have still been indistinguishable from a brand new structure after 1000 years.
I don't know. Everyone is free to believe what they want but I think I'll go with the published studies from professional engineers and material scientists on this one.
it seems like maybe a little bit you refer (indirectly) to planned obsolescence. that's certainly a thing. i don't know how popular that concept was two millenia ago. it's not something that i've ever seen discussed, to be honest. superficially speaking, it would seem to go against what i was taught about that time period, but as it was never directly mentioned, i have no idea. i just know how today's economy works (a little bit) and enduring structures aren't something we do anymore. i think that's the biggest reason we'll never build something like the cathedral of santa maria, ever again. that's sad to me, because men like bruneleschi were amazing and rare. not allowing that kind of person to carry mankind beyond the boundaries of what we know is possible, in a most beautiful way, is a huge loss
air handling systems, most especially in high rise towers, and other industrial applications has been my trade for 38 years. i have spent enough time in high rise office towers, i can confidently say that there isn't anything significant that would be a hindrance. if anything, it gets easier in some ways. equipment now is smaller, lighter, and more efficient. systems are alot more modular than they were as well. i can't speak of the other trades, someone else would know more.
you make me think of something here i hadn't considered before. maybe we might not want a structure like a sports complex or similar to last that long. it might be better to replace them every so often, for reasons other than durability. for example, what if you built a really awesome stadium, but 50 years down the road, the area fell into decline? maybe no one would want to go there anymore. or maybe it would be too big, or not big enough. maybe locals might decide they don't want it there anymore because traffic or other reasons.
i don't want you to take any of the stuff i said as some sort of argument. i never intended it that way. i just thought the discussion was really interesting.
No, there is no quarrel. Just differences in perceptions and likely differences in facts. I am not an engineer, but most of my career was in public works construction and I did need to understand, generally, the work involved and the materials, etc. For as long as I can remember, it has been generally accepted that even poor concrete mixes continue to cure and harden for at least 80 years. What I am pushing back against is this wholly false mythology about modern concrete mixes lasting maybe a couple of decades before they crumble. This is fully untrue.
There is quite a bit of science in concrete mixes and engineers call for a wide variety of them depending on application. There is just no way that humans understood concrete better 2000 years ago than they do today. Anymore than they understood medicine better 2000 years. This is patently false on its face.
We have now are anecdotal assertions backed by....only the assertions themselves and not much else....that do not comport with what we can observe everyday. We see an ocean of modern structures which are doing just fine, and a few ancient structures most of which are sorry-looking.
There are two bridges connecting Tacoma and Gig Harbor, each nearly a mile long. They sit in water with 15-foot tidal swells and 7-know currents. Occasionally ferocious winds offer hard-to-fathom shearing loads. The oldest of these bridges is more than 80 years old and is doing fine. The newest one, with concrete towers rising more than 500 feet above the water and carrying the suspension cables which support the entire weight of the bridge, was built in 2007. Anyone thinking the Romans could have built this is dreaming. Anyone wanting to learn more about concrete mixes can do so. There is a mountain of literature. The concrete mix used on the 2007 bridge contains no aggregate. It is mostly just Portland Cement, but does have some important additives. That concrete is "pozzolanic" silica-fume concrete which is what the MIT article discusses. This is not just something MIT discovered a month ago. This type of concrete is well-known and has been for many years. Here is an example of an older structure built with this amazing Romans-are-smarter-then-our-modern-engineers concrete:
As you can see, the Colisseum is not exactly doing well these days. But for the structural improvements (designed by modern engineers) to preserve it, it would be a pile of rubble now.
I dunno who wrote that MIT article, but it is somewhat fictionally sensationalized. Perhaps a journalism student? The only criticism of modern concrete that I see in the article is this: "Meanwhile, many modern concrete structures have crumbled after a few decades," which is a stretch on its face. I see failing concrete at times. My driveway has a spalling problem which was caused by a hurried builder placing and finishing the concrete in the wrong weather with no thought to durability. But "crumbling" modern concrete structures are many decades old, at least. Not exactly what I would call "several," personally. And certainly not how public works projects have been designed and built in my lifetime. I am 65.
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."
There is quite a bit of science in concrete mixes and engineers call for a wide variety of them depending on application. There is just no way that humans understood concrete better 2000 years ago than they do today. Anymore than they understood medicine better 2000 years. This is patently false on its face.
We have now are anecdotal assertions backed by....only the assertions themselves and not much else....that do not comport with what we can observe everyday. We see an ocean of modern structures which are doing just fine, and a few ancient structures most of which are sorry-looking.
There are two bridges connecting Tacoma and Gig Harbor, each nearly a mile long. They sit in water with 15-foot tidal swells and 7-know currents. Occasionally ferocious winds offer hard-to-fathom shearing loads. The oldest of these bridges is more than 80 years old and is doing fine. The newest one, with concrete towers rising more than 500 feet above the water and carrying the suspension cables which support the entire weight of the bridge, was built in 2007. Anyone thinking the Romans could have built this is dreaming. Anyone wanting to learn more about concrete mixes can do so. There is a mountain of literature. The concrete mix used on the 2007 bridge contains no aggregate. It is mostly just Portland Cement, but does have some important additives. That concrete is "pozzolanic" silica-fume concrete which is what the MIT article discusses. This is not just something MIT discovered a month ago. This type of concrete is well-known and has been for many years. Here is an example of an older structure built with this amazing Romans-are-smarter-then-our-modern-engineers concrete:
As you can see, the Colisseum is not exactly doing well these days. But for the structural improvements (designed by modern engineers) to preserve it, it would be a pile of rubble now.
I dunno who wrote that MIT article, but it is somewhat fictionally sensationalized. Perhaps a journalism student? The only criticism of modern concrete that I see in the article is this: "Meanwhile, many modern concrete structures have crumbled after a few decades," which is a stretch on its face. I see failing concrete at times. My driveway has a spalling problem which was caused by a hurried builder placing and finishing the concrete in the wrong weather with no thought to durability. But "crumbling" modern concrete structures are many decades old, at least. Not exactly what I would call "several," personally. And certainly not how public works projects have been designed and built in my lifetime. I am 65.
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."
In a black&white world, everything is concrete. Be watchful, regarding how it's all being reinforced. Therein lies the answer, sometimes.
We have a bridge down here called the Gladesville Bridge.
I remember it being said that this one is, or was, the largest single-span concrete bridge in the world. That filled me with pride, back then. True enough.
"The Gladesville Bridge is a few kilometres upstream of the famous Sydney Harbour Bridge. When it was completed in 1964, Gladesville Bridge was the longest single span concrete arch ever constructed."
These days, that stat is more likely to fill me with dread. We live and learn. Spare a thought for those in Western Asia who are caught up in that earthquake nightmare there — 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.
"The Gladesville Bridge is a few kilometres upstream of the famous Sydney Harbour Bridge. When it was completed in 1964, Gladesville Bridge was the longest single span concrete arch ever constructed."
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