Scientists replaced 40 percent of cement with rice husk cinder, limestone crushing waste, and silica sand, giving concrete a rubber-like quality, six to nine times more crack-resistant than regular concrete. It self-seals, replaces cement with plentiful waste products, and should be cheaper to use.

[u/mvea]

https://newatlas.com/materials/rubbery-crack-resistant-cement/

[u/Opeewan → u/[deleted]]

Obviously they didn't and either came up with their recipe through trial and error or it was a lucky coincidence.

[u/Oklahom0 → u/[deleted]]

Pompeii seems a likely guess. Imagine if you were a scientist who didn't have a word for volcano and heard of the horrors of Pompeii. And because these people are digging through this stuff, they probably noticed how it was getting harder and harder to dig up the ash.