GabyThese buildings have survived for millennia. And that’s because ingenious ancient Roman engineers knew the recipe for durable concrete.
So it’s no surprise that colossal structures like Colosseum and the Pantheon (the building with the largest unreinforced dome in the world) have stood for more than 2,000 years. Even buildings erected in earthquake zones and other challenging sites have survived to this day.
Researchers from the U.S., Italy, and Switzerland found that Roman concrete outlasts modern concrete, which often deteriorates within decades. Their team identified a previously unrecognized ingredient that made the ancient Romans’ building material so strong.
Scientists analyzed samples of two-thousand-year-old concrete taken from archaeological excavations in the commune of Privernum in central Italy. Compositionally, these pieces match other concrete samples found across the Roman Empire.
As researchers found, white lime fragments in the concrete gave it the ability to heal cracks that formed over time. Previously, those inclusions were dismissed as the result of careless mixing or low-quality raw materials, so scientists had not considered them when studying ancient building materials.
Admir Masic, an associate professor in the Department of Civil and Environmental Engineering at the Massachusetts Institute of Technology, told CNN that it was hard to believe ancient engineers failed in their tasks; they always carefully selected and processed their materials.
Masic said this discovery could help manufacturers produce more durable, refined concrete. That strong material allowed the Romans to achieve an architectural revolution and build extraordinarily beautiful cities.
What else did the researchers find out?
Concrete is created by mixing cement (an inorganic hydraulic binder), fine and coarse aggregates, and water. In a study published in the journal Science Advances, scientists concluded that the mixing methods hold the key to the durability of ancient structures.
Masic said Roman texts recommend using slaked lime as a binder — that is, lime mixed with water — so researchers originally believed Roman concrete was made that way.
However, laboratory analyses showed that the white lime fragments that provided the material’s stability formed from quicklime used at extremely high temperatures. This “hot mixing” of quicklime with other components is key to explaining the concrete’s durability.
Masic noted that those high temperatures sped up the chemical reactions in the mix and caused it to harden faster. That allowed builders to construct structures much more quickly.
To test whether the white fragments matched the self-healing ability of Roman concrete, the team made two concrete samples: one using the Roman recipe and one made to modern standards. They deliberately cracked both samples. After two weeks, water no longer seeped through the Roman-style concrete, while it still passed easily through the modern sample.
The team said that understanding this self-healing potential could lead to more durable modern concrete and help reduce concrete’s carbon footprint, which currently accounts for up to 8 percent of global greenhouse gas emissions.
For years, materials scientists, historians, and architects have credited the strength of Roman concrete to volcanic ash from Pozzuoli. That ash, widely used in Roman construction, has long been considered an important ingredient in concrete production.
Now scientists know another secret behind the durability of this ancient building material.
