New Study Reveals Rome’s Eco-Friendly Construction
As well as being just as durable, Roman concrete was also more eco-friendly than our modern recipe, which consists of lime and clay. This mixture requires that it be heated at high temperatures and results in significant carbon dioxide emissions. Roman hydraulic concrete, on the other hand, was made from pumice, mortar, lime and volcanic ash from Italy—pozzolana—and fired at much lower temperatures, thereby creating the more eco-friendly Roman concrete. While it takes longer for the Roman concrete to set, it is just as durable as modern concrete. A full report of Monteiro’s findings was posted online in the Journal of the American Ceramic Society on May 28.
BAS Library Members: Read more about Herod the Great’s use of hydraulic concrete at Caesarea Maritima in Kenneth G. Holum, “Building Power: The Politics of Architecture.” BAR September/October 2004.
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This summer, the Jezreel Valley Regional Project teamed up with Israeli archaeologist Yotam Tepper to expose a Roman camp just south of Tel Megiddo known as Legio. In a web-exclusive report, directors Matthew J. Adams, Jonathan David and Yotam Tepper describe the first archaeological investigation of a second-century C.E. Roman camp in the Eastern Roman Empire.
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Way cool! Some very valid points! I appreciate you writing this article and also the rest of the site is extremely good.
Thanks for giving some specific numbers. I would have thought that in, say, 500 years, walls and piers of reinforced concrete would totally collapse after the rebar had turned completely to runs and left voids that cold then completely fill with water and freeze. I have speculated, in an unpublished science fiction novel, that the cooling tower of a large nuclear reactor, 3000 years after its shutdown, would resemble a pile of onion rings collapsed on one another. Maybe it would happen much sooner (especially if waste radiation changed the chemical composition).
A recent TV documentary told of the attempt to build an unusually shaped wall for an art museum in Rome which was having problems because modern concrete emits too much heat while setting, and the shape required large sections to be poured at once; the modern architect used Roman cement for that part of the wall because it can be poured in larger segments without overheating.
The compressive strength comparison is interesting, but I still believe the rebar would be the downfall (literally) of modern concrete structures not lying flat on the ground. And maybe someone knows whether the Roman formula could be duplicated with raw materials from other parts of the world.
The compressive strength of Roman concrete is highly variable. In the linked study the average is about 1700 psi or around half the minimum compressive strength of modern everyday concrete (3000 psi). Some modern concrete mixes have compressive strengths over 8000 psi.
JAllan, I’m not sure about your estimate of centuries for the degradation of reinforced concrete. Anyone who lives in or near Toronto knows about the woes of concrete deterioration on the Gardiner Expressway (a deterioration process accelerated by the presence of road salt and the rapid freeze/thaw cycles experienced by an exposed, elevated roadway set close to a major body of water). But hey — I’m sure future archaeologists won’t miss the Gardiner.
Another great example of Roman materials science and engineering is found in their road construction. Fascinating stuff.
I think a bigger question is that will our structures be around in 2000 years. Somehow I doubt it. Yet the Roman ones clearly stand the test of time.
Actually, unreinforced concrete has the same strength under COMPRESSION as reinforced. Our modern concrete has steel imbedded in it (hence the term “rebar”), often with the steel stretched while the concrete sets, so that sideways forces, which result in the near side being stretched and the far side being compressed, are transferred to the steel and then from the steel to the concrete as compression. That is why we can build things that the Romans could not, such as tall buildings and bridges, out of concrete.
But there is a disadvantage to reinforcement: over EXTREMELY long times, such as many centuries, water will slowly seep inside the concrete and begin to rust away the rebar, and in cold climates it will also freeze and expand, opening up cracks for more water. Plain concrete, used in things that only have compressive loads (such as road surfaces), has a long term survival advantage over reinforced, unless the reinforced is maintained and occasionally rebuilt.
On the other hand, Roman concrete was made ONLY using the volcanic ash under Rome. Is there another globally available substitute for that ash? Possibly recycled concrete?
more durable maybe, but half the strength