Researchers discover why Roman concrete lasted so long

Researchers have discovered the reason why ancient Roman concrete has held up throughout history – not only because of its ingredients but also how it was mixed.

In a study conducted by scientists at MIT and Harvard University and released on Friday, researchers discovered that Romans used a mixing process called “hot mixing” in order to create a more durable form of concrete. 

As MIT professor Admir Masic explained to MIT News, “The benefits of hot mixing are twofold. First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form.”

“Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction,” Masic said, adding that they came to realize the concept after noticing extremely small white minerals in the concrete.

These deposits were once thought to be a weakness in concrete, but researchers now believe it’s the opposite.

“The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me,” Masic told MIT.

Researchers now know that the white mineral is calcium carbonate, which was formed after the concrete had been mixed at an “extreme temperature.”

“If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product?” Masic said.

Researchers will use their newfound knowledge to try to improve the quality of modern concrete.