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/xcvbsdfgwert]

Also note that longevity of the original Roman concrete has not (yet) been reached in modern times, i.e., the original recipe was lost.

[u/Shamhammer → u/[deleted]]

We know what's in it. But we dont know the exact chemical process that made it. What heat, additional additives that burned off, and how long are all important steps we may not know.

[u/WhiskeyElement → u/Shamhammer]

Blood of heathens is hard to come by these days

[u/SauronOMordor → u/WhiskeyElement]

But there are so many of us!