Let’s talk about something concrete

While in Rome, I visited the Pantheon for the first time. It was a humbling experience walking into this 2000 years old monument that boasts the largest unreinforced concrete dome in the world. The Romans are credited for inventing concrete, which allowed them to build their empire. As such, I want to talk about concrete before talking about the Pantheon. I will not be offended if you skip this post. It is a bit technical. But if you are interested, let’s make concrete.

To make concrete, we first need to make cement. The process starts by collecting rocks. Not any type of rocks. We need limestone, which contains calcium carbonate, and rocks that contain silicate. Grinding those rocks make a powder. We heat this powder to a temperature of 1450 degrees and add aluminium and iron. When this cools down we are left with a grey powder. This is cement.

How did the Romans figure out this process? They did not. They got lucky. The Romans found ready-made cement in Pozzuoli near Naples. This region is characterized by an accumulation of lava and ash from volcanic eruptions taking place over millions of years. The chemical reactions in a volcano are similar to the ones for making cement. The Romans only had to mine the rock powder.

The Romans figured out, however, to make concrete by adding water to cement. This creates chemical reactions that form a gel. The gel is made up of an internal skeleton composed of calcium silicate hydrate fibrils. The fibrils grow and mesh together locking in more and more water until the gel turns to a solid rock. This is concrete.

The fibrils within the concrete can bond with stones and rocks to make harbours, aqueducts, and monuments such as the Pantheon. Thus, concrete was a key ingredient for the Romans to build their empire.

If you are still with me, thank you! Next post, I will talk about the Pantheon and its concrete dome.

This two-part series is written by my husband, the guy in the Italia cap.