Portland cement

So it's cement with a long grain.

It's Portland type 2 cement, which is really good cement.

with long grain cellulose fibers in it.

So basically the concept of it is you get the flexibility and workability of like a wood product, only all the benefits of cement.

And the textbook draws specific attention to the modern cement industry's role in this.

We have to differentiate between ordinary Portland cement, known as OPC, and Portland pozzolana cement, or PPC.

And PPC is incredibly common globally.

The textbook notes that practically all cement industries in India use it, for example.

Yeah.

And of course the Romans knew how to do this, but then that technology was lost and then it was found again in England, in Portland, which is why it's called Portland cement and, and immediately applied to lighthouses.

One thing that I didn't know, though, is that those early lighthouses actually dovetailed their stone in order to hold it together.

I learned that, too, and that's part of the reason that they taper.