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Ancient Roman Concrete Is About To Revolutionize Modern Architecture
schwit1 sends this news from Businesweek:
"After 2,000 years, a long-lost secret behind the creation of one of the world's most durable man-made creations ever — Roman concrete — has finally been discovered by an international team of scientists, and it may have a significant impact on how we build cities of the future. Researchers have analyzed 11 harbors in the Mediterranean basin where, in many cases, 2,000-year-old (and sometimes older) headwaters constructed out of Roman concrete stand perfectly intact despite constant pounding by the sea. The most common blend of modern concrete, known as Portland cement, a formulation in use for nearly 200 years, can't come close to matching that track record. In seawater, it has a service life of less than 50 years. After that, it begins to erode. The secret to Roman concrete lies in its unique mineral formulation and production technique. As the researchers explain in a press release outlining their findings, 'The Romans made concrete by mixing lime and volcanic rock. For underwater structures, lime and volcanic ash were mixed to form mortar, and this mortar and volcanic tuff were packed into wooden forms. The seawater instantly triggered a hot chemical reaction. The lime was hydrated — incorporating water molecules into its structure — and reacted with the ash to cement the whole mixture together.'"
From http://newscenter.berkeley.edu/2013/06/04/roman-concrete/ While Roman concrete is durable, Monteiro said it is unlikely to replace modern concrete because it is not ideal for construction where faster hardening is needed. But the researchers are now finding ways to apply their discoveries about Roman concrete to the development of more earth-friendly and durable modern concrete. They are investigating whether volcanic ash would be a good, large-volume substitute in countries without easy access to fly ash, an industrial waste product from the burning of coal that is commonly used to produce modern, green concrete. “There is not enough fly ash in this world to replace half of the Portland cement being used,” said Monteiro. “Many countries don’t have fly ash, so the idea is to find alternative, local materials that will work, including the kind of volcanic ash that Romans used. Using these alternatives could replace 40 percent of the world’s demand for Portland cement.”
pasta.
The Romans ate bread, not pasta. Noodles were invented in China, and didn't reach Europe until the late middle ages. The first record of pasta being made in Italy was in 1154.
The problem is that it's the rebar itself that often destroys the structure. Concrete is porous, and so water finds it's way into the structure and gradually corrodes the rebar. The problem is that rust (iron+oxygen) is considerably larger than the original iron, and since concrete can't stretch to accommadate the expansion it eventually gets torn apart.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
If you really want to check facts, the Vatican was first recognized as a separate nation in 1929 a.d. by the Lateran Treaty, signed by representitives of the then current pope on one hand and Benito Mussolini on the other. 1929 is just a tad later than the end of the Roman empire.* Maybe you are thinking of 'the' Holy See,** or some of the Papal Estates that went back to at least Medieval times.
* Watch someone post "citation needed".
**Technically, any Bishop's diocese is a See, and presumably at least some Bishops in some eras have been not particularly unholy, so what the Pope, as Bishop of Rome, has, is merely a holy see, even though a lot of lay people seem to use the term like he has a lock on it.
Who is John Cabal?
Question is - why is it necessary for concrete to be reinforced? Obviously, the Romans didn't have steel or iron rebar. They formed and poured their structures without any rebar, and they've lasted a couple thousand years. It seems more than obvious that our architects and engineers can learn a few things from the Romans.
IANASE (structural engineer), but from my understanding one key difference that reinforced concrete confers is that it allows the concrete to be prestressed to perform better under tension. Concrete (Roman or modern) is just fine under compression, so it can support a prodigious amount of weight loading down on it. However, once you try to span an area then the concrete in the middle of the span is normally under tension. As you can imagine, this often leads to cracking and outright failure. Furthermore, it's why the Romans had such a predilection to using arches and domes, which keep the concrete predominantly under compression rather than tension.
Think about it this way: our highway bridges couldn't be built the way they are if we were using unreinforced Roman concrete; however, if the concrete is prestressed then the tensile forces are balanced by the compressive forces. This also allows us to do many other interesting things with architecture that weren't feasible before.
I have wondered about whether something like carbon fiber could be used in the future to produce prestressed concrete that wasn't as prone to corrosion as the steel rebar-based approach. Something like that might be the best of both worlds. Okay, so I just Googled and it looks like at least one carbon-fiber approach is already patented.
Just as an aside, the Romans were quite ingenious when it came to implementing their architectural application of concrete. I read that when Hadrian ordered the construction of the current version of the Pantheon, the Roman engineers were faced with difficulty designing a dome that would not collapse under its own weight (again, tensile forces and concrete are not friends). The Romans overcame this by reducing the density of the concrete in the dome by using pumice in the aggregate and reducing the thickness of the concrete as the dome progressed. The dome of the Pantheon remains the largest unreinforced concrete dome in the world—not because we can't replicate the techniques, but because reinforced concrete performs so much better under tension.
Actually atom size is only very loosley related to atomic weight - size does increase as you move down the periodic table in a single column (more electron shells), but it actually shrinks as you move to the right (tighter bonding between electrons and the nucleus). Basically the discrepancy is because atomic mass is determined almost entirely by the nucleus, which is several orders of magnitude smaller than the entire atom. Size on the other hand is determined by the arrangement of the electron cloud.
For a quick visual reference: http://www.crystalmaker.com/support/tutorials/crystalmaker/atomicradii/
Notice that a lithium atom, with an atomic mass of only 7, is actually about the same size as bismuth, which has an atomic mass of 209
And the basic fact is that the oxide can't possibly be the same size as the original material. Common rust has the chemical formula Fe2O3, which means that where you used to have only two iron atoms, you now have two iron atoms PLUS three oxygen atoms. But you are right that the basic strategy is to prevent flaking, if we could somehow "convince" the oxide to form hematite crystals instead of flaking away corrosion would be a non-issue. That's why highly reactive aluminum appears to be so stable, the oxide readily forms a thin crystaline layer bonded to the metal which prevents further oxidation (basically corundum, the base gemstone of rubies and saphires). Disrupt the oxide layer and the aluminum will *very* rapidly rust away, as in you can actually see a beam "dissolving" in front of you - that's why they don't allow mercury thermometers on airplanes, mercury is one such disrupting agent and a spill could cause the aircraft to come apart in the air.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Turns out its not the ash that mattered.
Its just the composition of the particular variety of ash they had on hand. Volcanic ash differs in various volcanic regions. Further, seawater was also key. You don't find much of that in the middle of continents.
This wasn't ancient knowledge at work at all. It was simply an accident of geography.
Is it really any different from the fact that availability of raw materials in any region is an accident of geography?
If you read TFA you will see that:
A) the Romans were well aware which ashes were the best for this purpose. Vitruvius and Pliny wrote about it. It is not as if they were mystified why this hydraulic cement was turning out so well. Sure they didn't understand the chemistry, but they tried many ashes and knew the ones that had special properties.
B) The researchers found this concrete in 11 harbors around the Mediterranean. This means the Roman were exporting their special ash to where it was needed for harbor construction.
Sounds like ancient knowledge to me. (Otherwise you are going to have to hold that none of the material production skills before modern times were really ancient knowledge.)
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
Speaking as somebody whose family has lived on the ocean for over 18 years, marine-grade stainlees is pretty near impervious to seawater. You need to check it periodically, of course, but if you use the right stuff (which is closer to the "20x cost of mild steel" end of the range) it will happily endure for a very long time without even significant discoloration. Of course, it helps there the boat also has zincs and that we're careful about dissimilar metals and so forth. Nonetheless, a really good grade of stainless (one way to tell is to check with a powerful magnet; good stainless is not noticeably magnetic) is able to endure seawater much better than you imply. You just can't be cheap about it... which makes it impractical as a building material in most cases.
There's no place I could be, since I've found Serenity...