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[h/t BeninSC]
The dome of the Pantheon in Rome, nearly 2000 years old, even now, is the largest dome made of unreinforced concrete. The Pantheon as a structure is exemplary of the durability of Roman concrete. Another example are the concrete seawalls constructed by the Romans, which have survived two millennia of the battering of storms and tides. Modern unreinforced concrete, on the other hand, crumbles to pieces on much shorter timescales. What did the Romans do to create a building material that could survive for so long?
Roman concrete is sometimes called pozzolanic concrete, because one of its ingredients is volcanic ash. (This volcanic ash is called pozzolana because there’s a rich supply of it near the town of Pozzuoli.) In addition to pozzolana, the other ingredients in the known recipe for Roman concrete are water and lime. Lime is generally a combination of calcium oxide (CaO), also called quicklime, and calcium hydroxide (Ca(OH)2), also called slaked lime. The three ingredients are then assumed to react together to form this highly durable material.
Researchers at the Massachusetts Institute of Technology (MIT) have discovered that pozzolanic concrete is not homogeneous. If you break apart a piece of Roman concrete, you will find chunks, called clasts, of unreacted lime within. It turns out that the presence of these lime clasts is key to the concrete’s durability. If a crack forms in the concrete, the crack will eventually reach one of these clasts, where the lime can react with water and carbon dioxide that diffuse through the crack to produce calcium carbonate, in form of the mineral calcite, which acts like a glue to repair the crack:
CaO + CO2 → CaCO3
The researchers also determined that the process of making pozzolanic concrete required much higher temperatures than previously thought, which results in more rapid concrete formation and curing.
So, the team tested their findings by making pozzolanic concrete from ancient and modern recipes using quicklime. They also made a control concrete without quicklime and performed crack tests. Sure enough, the cracked quicklime concrete was fully healed within two weeks, but the control concrete stayed cracked.
The team is now working on commercializing their concrete as a more environmentally friendly alternative to current concretes.
Comments are below the fold.
Top Comments (March 17, 2024):
From wandering in samsara:
I'd like to nominate a comment by G2geek in Frederick Clarkson's diary, This is not a hoax. G2geek points out that "a healthy sense of self worth" requires participation. Science may inspire, but the average person can't participate in it. And for so much of our entertainment, we are a passive audience, not participants. "Trumpism, populism, fascism" offer people participation. We need to counter this with our own participatory opportunities, and G2geek suggests one possible way of doing so.
Highlighted by GCNY:
This comment by Franks Human in today’s IAN diary by loggersbrat.
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Top Photos (March 16, 2024):
Thanks to jotter (RIP) for creating it and elfling for restoring it!