Nice article, and this is certainly a topic that everyone should know a little about seeing how fundamental cement is to our civilization. But it left out something very important at the end there... steel reinforced concrete is fantastic stuff of course, but it also comes with a drawback that is about to cost us very dearly; it doesn't last very long. All of our magnificent bridges and fantastic architecture come with a built-in expiration date because the steel inside them is rusting. That expiration date is somewhere between 50 and 150 years, and for a lot of our infrastructure it's coming due.

Concrete made from portland cement is waterproof but it isn't moisture proof, nor airtight. It breathes just enough that the oxidation of steel isn't completely stopped. And when the rebar rusts it expands, which causes the concrete to crack, letting more moisture and air in, causting the rebar to rust faster.

There are solutions to this problem, such as using rebars made from materials less susceptible to rust (stainless steel or even carbon fiber), but for the most part they are either a lot more expensive or nowhere nearly as strong. And there is susprisingly little research into this considering how important it seems... our civilization isn't very good at committing resources to things that have payoffs longer than 50 years, so everyone continues to use plain old steel as rebar in their constructions. Meanwhile, the Roman pantheon remains standing, perhaps another couple of thousand years?