The Concrete Poured By The Romans Was Way Better

The concrete mixture used by the Romans wasn’t the same as what your Uncle the mason uses, not likely. That recipe, while not eternal, has stood the pounding of the ocean in places for thousands of years. What is more surprising is that we’ve only recently figured out how to make it again.

On only need travel in the developing world or the undeveloped parts of the United States to see how far today’s concrete goes. After a few years, it crumbles, breaks off, and falls apart. It’s sad. Bad architecture aside, it’s too bad there wasn’t some way to make concrete that could last longer. Well, there is, there was.

The mixture of concrete, championed by our Roman predecessors, known as opus caementicium, poured itself into history during the late Roman Republic dating until its demise. The projects built from that ‘crete, including ocean harbor projects, remain almost intact in many places. In some cases, they still stand, like the aqueduct.

This super concrete not only lasted against the sands of time, it also outperforms modern concrete methods with a smaller environmental footprint, begging the question: How the heck did we forget how to make the good stuff?

Opus Caementicium

The devil is in the details. To make their concrete, the Romans followed the same basic recipe we use today: aggregate (rocks), mortar, and a binder.

The aggregate only matters for the desired use. What is really impressive about concrete they poured was that they used no rebar. The steel rods that run through modern architecture, called rebar, we forge from steel.

How convenient that humanity discovered how to temper steel to compensate for our crummy concrete. Had we made it like the Romans, we may not need it or we may have even stronger building than they.

The binder was the key difference. Romans used volcanic dust, something they called pozzolana. As we’ve since figured out, pozzolana is more resilient, even resistant to salt water.

What We Know

Today’s usual mixture of concrete is something called Portland cement, which uses limestone power with no volcanic ash. It lasts about 50 years in water before needing replacement or attention.

The general consistency of limestone ash compared to the volcanic dust is about the same, but the mineral properties are not.

Limestone is caustic, causing chemical burns with regular exposure. Mining limestone is costly and harmful to the environment, but access to limestone is easy.

Builders regard Portland cement is the most versatile building material in the world. To our credit, that which we pour today are ten times stronger than what we poured in the mid 19th century.

It’s still not as plastic as Roman concrete.

New Roman Concrete

After a team of researchers from Italy and the United States analyzed a sample of Roman concrete from around 37 BCE, they determined what exactly made up this magic material.

The solution to the problem was not as much an issue of knowing the materials. Writings from the time celebrated the virtues of concrete poured using volcanic ash.

Figuring what it was about that ash that made it better, what the best ratios of those elements were to replicate opus caementicium, was what we needed. As it turns out, the Romans did not keep a web database of concrete recipes.

The research, completed at labs at U.C. Berkeley, in Saudi Arabia, and in Germany were able to determine the secrets from their sample.

What they found was that the seawater was as much as part of the chemistry as the volcanic ash. Whether the Romans knew it or not (likely not) it was that component of seawater that bonded the elements together.

Environmental Impact

About 7% of the Earth’s carbon dioxide comes from the production of Portland cement, which isn’t too bad considering it’s used everywhere. Still, any decrease in carbon footprint is generally considered good, especially if it costs industry no more money to adopt.

The heat required to produce a limestone product we can use requires a furnace of 2,642 degrees Fahrenheit. Roman concrete uses much less limestone, and the furnace temps to produce it are only 1,652 degrees. That means the fuel expense alone is 30-40% more efficient.

Adding to that, the concrete poured will last longer, which means builders will have to replace it less frequently. The durability also extends where and how we can use it.

While widespread use of what these researchers discovered is not yet a common practice, we now have the know-how to improve our uses of concrete. Hopefully, we don’t spend another 1500 years getting in back into practice.