HOKAY. Doing this in layman’s terms because I could not explain the chemistry in detail if I tried. Pls forgive if I’m a little off in the explanation because idk chem lol
So we’ve been trying to figure out why the fuck Roman concrete has held up so long, right? Our concrete lasts maybe like ten years before it looks like it took a wrecking ball to the face. And even then, our roads suck in general. Universally. Potholes. Everywhere.
Roman concrete has lasted two thousand years. Or more. Depends on where you go.
Now a bunch of scientists took chunks of concrete and threw a bunch of waves at it to figure out the composition, and turns out the concrete has lime in it. At first they were like “Huh, that’s weird, why are these imperfections in this super durable long-lasting concrete?”
So anyways they dismissed the lime, and they also figured out that Roman concrete is suuuuuper strong in water. Like it gets stronger in water. Compare that to our shitty ass concrete. Our concrete suffers in water. It’s shit. Our concrete is a middle-schooler’s newspaper bridge project compared to the Bifrost that is Roman concrete.
Now, because chemical composition is fairly easy to figure out, they found volcanic ash. We don’t have volcanic ash in our concrete (as far as I know), so idk I guess they thought that was the differential factor that made Roman concrete so strong. To my understanding, the Romans used hydraulic mortar rather than aerial mortar. Hydraulic mortar could harden with hydration and reactive silicates, whereas aerial mortar needed exposure to the air and was weaker.
Now, remember those imperfections I mentioned earlier? Lime is very, very weak. You ever felt limestone? Yeah. You get it. So it’s not hard to figure out why we thought these were actually imperfections in otherwise amazing, god-like, S-tier concrete. We used to think it was slaked lime, which is just lime paste.
One of the labs involved in the research developed a chemical mapping technique that allowed them to determine the exact makeup and type of lime present in the concrete. They figured out that this particular form of lime might have been quicklime, which is extremely brittle and very reactive. Quicklime forms at extremely high temperatures. We mix our concrete cold. Another common modern L.
In short, the Romans engineered preferential pathways for faults in the concrete to pass through the lime, which would react to hydration and recrystallize as more lime (calcium carbonate) and heal itself.
This is groundbreaking. I’m so amazed. Here’s the MIT publication, and here’s the journal article.
