It’s been a mystery why Roman concrete often lasted thousands of years, but ours decays in mere decades. Turns out they incorporated chemicals in a process that induces self-healing; scientists at MIT just figured this all out – in 2022.
Scientists in a MIT, Harvard University study found that Romans actually relied on a process called “hot mixing” to whip up their hyper durable concrete.
“The benefits of hot mixing are twofold,” MIT professor of civil and environmental engineering Admir Masic told MIT News. “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,” he added.
Masic was first alerted to the concept after noticing millimeter-small bright white minerals in the ancient concrete.
The outlet said these deposits, described as “lime clasts” and not found in concrete today, were once chalked up to poor mixing practices.
But the MIT professor took issue with this line of thought.
“The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me,” Masic told the publication. “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 and his team discovered that the white specs were actually calcium carbonate that had been formed after the mixture, which include quicklime, reached an “extreme temperature.”
His team then ran a series of tests using modern and ancient techniques with and without quicklime.
The team are now working to commercialize the ancient practices for modern use.