Ancient roman concrete hold infrastructure’s long life elixir

Rome was not built in a day. And this may be one of the secrets of its pact with eternity. A pact so solid that its most representative monuments, from the Pantheon to the Colosseum, are no longer mere symbols or a 2000 years old empire, but today are also the subjects of research in the search for answers to one of the most complex engineering questions: is there a material that can withstand the test of time?

Researchers at Boston’s MIT, one of the world’s most prestigious universities, are trying to answer this question, and their starting point is precisely the study of the materials used by ancient Romans to build works such as the Pantheon, which after two millennia still appears sturdy and lasting.

Such monuments not only survived the fall of the Roman Empire, but also wars, famines and bombardments. In other words, the passing of time. And according to the MIT researchers, who published an in-depth study just in the last few weeks, the key to the longevity of Roman buildings lies in the techniques used to mix the materials.

“The Pantheon would not exist without the concrete as it was in the Roman time,” said Armir Masic, MIT engineering professor and author of the study.

From the Pantheon to Boston, the materials with which ancient Rome’s monuments were built traveled thousands of miles to MIT’s labs, where researchers studied the makeup of that concrete which, as Pliny the Elder had predicted, became more solid as time went on.

“They knew that was a great material, but they probably didn’t know that it would last thousands of years,” Masic said.

MIT’s labs discovered that it all depended on the way the materials were mixed together.  Roman cement was produced by mixing volcanic rock held together with a special mortar made by mixing pozzolan, lime and water. In addition, Roman peers and dams were built with a concrete that contains aluminous minerals that add strength and durability.

This point was also highlighted by the British magazine The Economist, which recently quoted “De Architecture”, the first century B.C. work  on architecture by Marcus Vitruvius Pollio, an architect that, according to historians, also joined Julius Caesar in many military campaigns. In his books, the Roman scholar focused on concrete production techniques that would allow the material to resist the passage of time.

The Boston research, published in the periodical “Scienze Advances,” takes what was already known about Roman construction techniques a step further, adding interesting discoveries about the monuments of Ancient Rome that may be useful to the world’s construction industry in the coming years. The researchers examined a sample of Roman concrete from a wall in the ancient city of Privernum near Rome, revealing it contained different forms of calcium carbonate of a kind usually formed when there is a lack of water. This led to the conclusion that ancient Romans did not add water to the lime but ash, as recently reported by The Guardian.

Called “hot mixing” because of the heat it produces, this process helps the mortar to set and reduces the water content. When in time the concrete cracks and water seeps in, it dissolves calcium carbonate, and the concrete self heals as the materials react.

The team note calcium carbonate filled cracks have recently been found in Roman concrete.

“Roman-inspired approaches, based for example on hot mixing, might be a cost-effective way to make our infrastructure last longer through the self-healing mechanisms we illustrate in this study,” Masic said.