Thread by @cullenroche

This meme going around Twitter is fun.

The history and economics of hardscaping is actually very fascinating.

Cobblestone, or sampietrini, as the ancient Romans referred to it, is basically a cement surface with huge rock aggregates. That is, it's large stone connected with a cement bond. It's only as strong as the bonding agent used.

In the 16th century the Romans would heat limestone and mix sand to create mortar. It was a relatively low PSI concrete for various reasons.

Interestingly, Marcus Vitruvius, who made many of these discoveries, was considered a Roman "Engineer".

goodreads.com/book/show/5238…

The economics of cobblestone made sense in the 16th century mainly because slaves were a thing. But even to this day the economics don't work because cobblestone requires tremendous skill and labor to lay. That's why Rome is replacing their cobblestone.

travelandleisure.com/travel-news/ci…

Additionally, the stone in cobblestone is prone to potholes since the stones are simply too large. That's why modern day concretes use relatively small stone (usually 1 inch or so). This is also why you often see "NO TRUCKS" signs on cobblestone roads.

Which brings us to the real reason we don't use cobblestone (ie, large concrete aggregate roads) - cars. Due to the required upkeep of cobblestone and the increase in vehicle weight we engineered surfaces that could better withstand things like Mack Trucks.

Portland Cement (and the like) was one of the most important developments during the industrial revolution. This used finely ground clay and limestone that was fired until calcined. When you added strong stones you created a super strong concrete (cement + rock).

Modern day cement based concretes are super strong due to various changes in production technology and they are easy to pour for the same reason. But they are still expensive relative to other surfaces (such as asphalt).

Asphalt is like the cheap evil cousin of cement. It is a petroleum based bonding agent mixed with rock aggregate to create most of the roads we see today (asphalt concrete roads). It is inexpensive, weaker but also easy to pour.

The economics of asphalt vs cement roads are controversial. Most govts defer to asphalt because of cost. But you still have the cobblestone problem with the surface being pothole prone due to its relatively low PSI and flexibility (a short-term strength and long-term weakness).

Long story short, the engineers know all of this and have helped us make huge progress. But they've also run into govt budget constraints that limit the ideal materials we might use thereby making roads that appear worse than they could be.

Source: Just a big dork who goes to Home Depot almost every day. And I also poured about 10 tons of concrete in my backyard in the last 6 months and did my homework. :-)

* Oops. This should be 1st century Rome. Sorry for the mistake.