Massive, iconic structures like the Roman Colosseum and the Pantheon are so indelible and so fixed a part of the West's landscape that it's easy to forget that, uh, wow, they've been there for literally thousands of years.
When you realize that, a pretty reasonable question follows: How come that concrete sidewalk I poured is already cracking after just half a decade, but the frickin' Roman Forum still has massive columns standing after nearly 2,000 years?
Well, here's why:
Roman concrete, in many cases, has proven to be longer-lasting than its modern equivalent, which can deteriorate within decades. Now, scientists behind a new study say they have uncovered the mystery ingredient that allowed the Romans to make their construction material so durable and build elaborate structures in challenging places such as docks, sewers and earthquake zones.
As an aside, yes, the masonry is that impressive. By way of example, one ancient Roman aqueduct, the Acqua Virgo, was built several years before the birth of Christ and is still bringing fresh drinking water to Rome:
So what makes it all so unbelievably durable?
The study team, including researchers from the United States, Italy and Switzerland, analyzed 2,000-year-old concrete samples that were taken from a city wall at the archaeological site of Privernum, in central Italy, and are similar in composition to other concrete found throughout the Roman Empire.
They found that white chunks in the concrete, referred to as lime clasts, gave the concrete the ability to heal cracks that formed over time. The white chunks previously had been overlooked as evidence of sloppy mixing or poor-quality raw material.
So basically ancient Roman concrete had the ability to heal itself.
That'll keep you upright for 2,000 years!
Archeologists had originally assumed that ancient Romans used "slaked lime" as an additive in their concrete, but it turns out that they actually used quicklime, with a process known as hot mixing playing a key role:
"The benefits of hot mixing are twofold," Masic said in a news release. "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."
The importance of these developments to human history, meanwhile, were apparently massive:
"Concrete allowed the Romans to have an architectural revolution," Masic said. "Romans were able to create and turn the cities into something that is extraordinary and beautiful to live in. And that revolution basically changed completely the way humans live."
The full research was published in the Science Advances.