Technology Lost to Time Pt. II: Roman Concrete

The Romans are known for being engineering mad lads who couldn’t help but design some of the most wondrous architecture of the human era. Everything they did was big and grandiose. Their wars outshone all wars up to the Napoleonic Wars of the 18th Century. Their colonnades were ornately carved, their people were hearty and hedonistic. Their philosophy preached stoic piety and their politics weren’t complete without violent coup d’états.

Their Republic ran on slave labor from conquered peoples, and the Empire was hardly different.

So naturally, when I see the Wikipedia article referencing someone else’s statements without properly citing them as saying, “a candidate for the most durable building material in human history,” I get curious.

We know about Roman Concrete for a few main reasons. The first is the literal evidence left behind by the Romans in the form of some of their most majestic and in-your-face monuments like the dome of the Pantheon in Rome. As astonishing as it may seem, that hulking hunk of grey isn’t stone, but is in fact concrete. No rebar, no internal structural support whatsoever, actually. Roman engineers flexed on us modern plebs by pouring their concrete mix into a cast, similar to how they would a bronze sculpture. The dome is all one piece, and the weight is borne towards the center hole at the top, called a keystone hole. Roman engineers also pioneered keystone arches and took that concept a bit further with that keystone that serves as a glimpse of the modern Roman sky.

This is where Roman Concrete gets insanely interesting. Roman Concrete is the only hydraulic concrete that is not only able to withstand the tests of time, but use it to strengthen itself like a bodybuilder that just discovered creatine. The secret ingredient is the pozzolana, which makes it more resistant to saltwater than modern-day concrete. This is because of the high amount of silica and alumina that can be found in pozzolana. The longevity of Roman Concrete is understood to be the product of a chemical reaction that takes place between the seawater, volcanic ash (pozzolana), and quicklime to create a crystalline structure known as tobermorite, which strengthens the overall concrete structure and is part of the reason why Roman “Marine” Concrete lasts as long as it does. Essentially the seawater “percolates” into the tiny cracks, reacts with phillipsite, which is commonly found in volcanic ash, and produces the tobermorite crystal in those cracks, thereby strengthening the concrete.

As this article is growing rather long-winded, I’ll briefly discuss the modern issues we run into with Roman Concrete, its counterpart Portland Cement, and what that means for the future.

Many people state that the recipe was lost, though I just wrote it down above in not near enough detail to be considered scholarly, but enough to be considered concise. Many modern contractors, archaeologists, and chemical engineers speculate about the use of Roman Concrete in the modern day, essentially surmising that it has a plethora of environmental benefits considering the fact that it eliminates the need for rebar, and its longevity and marine use.

The two problems that arise when studying this fascinating subject are twofold. One, volcanic ash is rare and expensive to source, the Romans were lucky to have access to it since most pozzolana can be found in modern Italy from Vesuvius to Etna. Two being that reverse engineering Roman Concrete is difficult due to its sheer age. It gets stronger and stronger over time, making difficult to know what its tensile strength would have been in the beginning.

This is where Portland Cement comes into play as the modern solution to some of these problems. They replaced volcanic ash with a material known as fly ash, which is more widespread and up to 60% cheaper because it requires much less cement. I was unable to find a direct solution to the second issue, so much of Portland Cement has been a guess as far as tensile strength goes for any length of time beyond even a few centuries. For all we know, we’ve truly reinvented Roman Concrete without knowing it and put a modern twist on it.

In conclusion, I would like to propose a name-change for Portland Cement. We are following in the footsteps of our Roman forebears, and I believe we should honor them by naming it Roman-style Cement or something badass like that. Nothing against Portland, but Rome will always be the torch that burns at the heart of the West, and it is Rome whose foundations we have built upon. Quite literally, in fact. In homage to the Eternal City and its Eternal Concrete, I declare it to be badass and one of the most amazing discoveries of history.

(PS…Eternal Concrete is also pretty badass and Rome-inspired. Just a suggestion.)