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Why architectural marvels from Ancient Rome are still standing

SCOTT SIMON, HOST:

Ancient Rome wasn't built in a day, and some of its architectural marvels have lasted longer than most of us can fathom - like B.J. Leiderman, who writes our theme music. Consider if anything you've seen built in your lifetime would be standing nearly 2,000 years from now, like the Colosseum and Pantheon. The Romans apparently had a secret sauce, a blend of concrete that was a bit of a mystery until now. Admir Masic is a professor of civil and environmental engineering at MIT. Thanks so much for joining us.

ADMIR MASIC: Thank you for this invitation.

SIMON: What did you find when you looked into this durable blend of concrete?

MASIC: We found that there are key ingredients in ancient Roman concrete that lead to a really outstanding functionality property in the ancient mortar, which is self-healing.

SIMON: Self-healing - how so?

MASIC: So self-healing means that basically there are specific way how Romans mix their key ingredients, namely lime, volcanic ash and aggregates together with water. They mixed using this technique that is called hot mixing. Basically, mix heats up, up to, you know, 80, 90 degrees C, so equivalent of 180 degrees Fahrenheit. That is really unusual. You know, we, in modern time, we mix - do cold mixing, if you want to call it like that. Due to hot mixing and creation of these tiny granules of lime due to hot mixing, eventually you create a mechanism that that just naturally goes and fills the crack with the material and prevents water to flow and propagation of the crack.

SIMON: That's amazing. I mean, it sounds almost like partly what the human body does.

MASIC: Exactly. We like to compare it with the self-healing of our bones, indeed.

SIMON: Why did the exact nature of this composition elude us until your research just now?

MASIC: You know, engineers and scholars describe the formula of how to make a Roman concrete. And then, of course, they describe volcanic ash as a key ingredient, this miraculous addition to a traditional lime-based mortar. And we just ignored the lime as the key ingredient of a Roman concrete mix.

SIMON: Now, you point out that this ancient Roman concrete not only lasts centuries, but it would reduce the carbon footprint of making new concrete.

MASIC: Yeah. I mean, if we are able to build that next infrastructure that lasts longer, this will require less material and on the long run, that will eventually require less energy to maintain and eventually will correspond to less emissions. And so that's the first step, where we create a material that eventually is part of a solution instead of being a problem.

SIMON: Admir Masic is a professor of civil and environmental engineering at MIT. And his team's research has just been published in the journal Science Advances. Thanks so much for being with us.

MASIC: Thank you very much.

(SOUNDBITE OF SONG, "ROME (WASN'T BUILT IN A DAY)")

SAM COOKE: (Singing) But I know Rome wasn't built in a day. Listen to me, honey, now. How would Romeo feel if his Juliet had turned down his advances and played hard to get? He wouldn't have let this bother him, this I know, because where there's life, there's hope. Oh, baby, don't go away. Transcript provided by NPR, Copyright NPR.

Scott Simon is one of America's most admired writers and broadcasters. He is the host of Weekend Edition Saturday and is one of the hosts of NPR's morning news podcast Up First. He has reported from all fifty states, five continents, and ten wars, from El Salvador to Sarajevo to Afghanistan and Iraq. His books have chronicled character and characters, in war and peace, sports and art, tragedy and comedy.