Concrete for the Ages

Have you ever wondered how it’s possible for an ancient building like the Pantheon to still be standing?  Well, the Pantheon does have the distinction of being the best-preserved old building in Rome but there are many other Roman buildings that share the same solid staying power and it all comes down to the concrete.

Yes, we’re going to talk about concrete again!

This time, scientists are at the centre of the story because they’ve discovered the “secret” behind the durability of ancient masonry. The secret turns out to be the particular ingredients in the concrete they mixed, and in this story, it’s the specific mixture of lime and volcanic rock.

Nowadays, as we’ve discussed elsewhere on the website, the main ingredient in concrete is Portland cement. From a modern standpoint, it’s considered pretty durable stuff but a structure built today will have a limited lifespan (say 150-200 years at best) especially when exposed to certain elements and weather conditions. So when you consider the fact that the ancient Roman Colosseum and the aqueducts are still standing, you can understand why the scientists decided to delve into the matter. Apparently it was the underwater structures like harbours and breakwaters that really intrigued them. How could these structures survive the ravages of the Mediterranean sea and the salt water?

Well, salt water is one clue to solving the mystery. The Romans made their concrete of lime and volcanic rock or ash. For underwater structures, lime and volcanic ash were mixed to form the mortar base. With the addition of seawater, an instant and hot chemical reaction was triggered, cementing this powerful mixture together. Also the ancient Romans used much less lime in the creation of their cement compared to modern-day cement, according to the discovery by scientists from the U.S. Department of Energy’s Berkeley Lab at the University of California. It was determined that the ancient Roman formula contained aluminum (from the ash) and had less silicon than is contained in today’s Portland cement.

It’s widely understood that the manufacture of Portland cement for modern concrete creates harmful carbon dioxide emissions because of the fuel needed to produce it. This ancient recipe for concrete is considered much “greener” because it is less harmful to the environment, so it probably suggests some future changes in construction materials. Masons, builders and architects, take note!

Interesting Fact: The Pantheon contains the world’s largest un-reinforced concrete dome.