TIL ancient Roman concrete used seawater as a key ingredient, not just lime

Fiona Robinson · 2026-08-17T17:35:20.620675+00:00

I was reading a 2017 paper from Berkeley about Roman harbor structures, and it turns out their concrete actually got STRONGER from exposure to seawater because of a reaction with volcanic ash. My old professor always said they used plain lime and called it a mystery, but the real recipe is a mix of lime, volcanic tuff, and seawater that forms a rare mineral called aluminum tobermorite. I checked against a few digs I visited last summer in Italy, and the surviving piers match that exact chemistry. Why do textbooks still push the simpler story when the evidence has been public for nearly a decade? Has anyone else run into outdated explanations like this in field guides or museum plaques, and how do you correct them without sounding like a know-it-all?

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TIL ancient Roman concrete used seawater as a key ingredient, not just lime | Archaeology Discoveries - HW Forums