Although the Roman Empire fell more than 1,500 years ago, its ancient cement structures — like the Pantheon, Trajan's Markets, piers and breakwaters — remain.
To make concrete, Romans mixed volcanic ash with lime and seawater to create a mortar. From there, they added chunks of volcanic rock.
Geologist Marie Jackson has been studying factors that make Rome's concrete so durable. In 2013, she examined mineral and microscale properties of Roman concrete and found that unlike modern cement concrete, Roman concrete's filler is chemically reactive, making it stronger and more resilient.
Now, she's at least figured out how Roman concrete holds up so well in water. In a new study, Jackson found that seawater filtering through the ancient Roman concrete dissolves parts of the volcanic ash and allows interlocking minerals to grow that strengthen the material. In modern concrete, seawater would make the structure crack.
Jackson is trying to develop a similar concrete using materials readily available in the U.S.
Besides its durability, Roman concrete has also been found to have a smaller carbon footprint than its modern counterpart.
But despite these benefits, Roman concrete probably won't enter the mainstream. It can't support as much weight as the modern stuff and takes a long time to develop resilience.