The growing power of Rome’s monuments: the secrets of dynamic concrete. From the article: 

Engineers and materials scientists are still studying Roman structures today, and they say the secret is the marriage of ingenious design with an innovative recipe for concrete, a supremely durable and adaptable material that is still used the world over. While the Romans didn’t invent concrete, they certainly raised the bar for building with it….

The highest expressions of the Roman Empire’s built environment confront modern visitors with an “engineering approach”, said Renato Perucchio, a mechanical engineer at the University of Rochester in New York. “The Romans performed sophisticated analyses that led them to these designs, which were then expressed through an extremely careful construction process.”

The concrete that held these designs together was also unique and deeply considered. Roman concrete used a different recipe than modern concrete, and researchers studying this ancient material say its ingredients appear to endow the material with phenomenal resistance to degradation….

In contrast to modern concrete, this ongoing reactivity allows Roman concrete to get stronger over time. These long-term chemical reactions can serve to reinforce small cracks that often form between the pieces of aggregate and the binding cement and prevent them from propagating farther. This regenerative capacity, made possible by the reactive volcanic minerals, is what enables Roman concrete’s tremendous capacity to endure….

No visit to Rome would be complete without a visit to the Colosseum, but for anyone seeking the pinnacle of concrete construction in the ancient world, Perucchio says the Pantheon’s unreinforced dome is a must.

Inside the Pantheon’s rotunda, the distance from the floor to the very top of the dome is virtually identical to the dome’s 43m diameter, inviting anyone inside to imagine the huge, perfect sphere that could be housed within its interior. When trying to appreciate the Pantheon’s dome, “unreinforced” is really the key word….

“The dome creates very high tensile stresses, yet it’s been standing for 19 centuries,” said Perucchio. “From this you can draw one of two conclusions: either gravity worked differently in Roman times; or there is knowledge that we have lost.”…

[Admir] Masic and [Marie] Jackson are studying Roman concrete with an eye towards making today’s concrete more environmentally friendly. The biggest advantage of Roman concrete, Masic said, is that its lime-based binder only needs to be heated to around 900C, while portland cement needs to be fired at close to 1,450C.

This alone means that Roman concrete has the potential to offer massive reductions in the carbon footprint of concrete production. But Masic said the material’s’ longevity could also allow us to replace infrastructure less frequently.