What made Roman concrete so durable?

“What survives is proof of the fact that the technology they had was durable,” says Ferrara. But the concrete is only part of the reason so many ancient Roman buildings still stand, he explains. “You have the material, but you also have a way in which you use the material. We cannot decouple these two concepts.”

One of the special ingredients in Roman concrete was ‘pozzolana’. These volcanic rocks, which would have been widely available around Rome, react with the water used to hydrate the concrete, and in doing so improve its overall durability.

But the way the concrete was used within the structure was just as crucial to a building’s long-term survival, adds Ferrara. Roman structures – as anyone who has visited the Pantheon can attest to – were massive. Concrete was incorporated into buildings that worked under compressive stress, which also helped them stand the test of time.

On the other hand, the loads placed upon buildings and bridges would have been far smaller than today. “On a Roman bridge, it’s mostly just carts with horses and goats,” says Ferrara.

“They had the armies which would have been very demand-loading, but it''s completely different from what we demand for structures in cities nowadays,” he notes.In the EU-funded ReSHEALience project, Ferrara developed a series of mixtures to develop ultra-high durability concrete for use in marine structures and energy plants. The severe environmental conditions faced by these kinds of structures shortens their lifespan, leading to large financial costs each year for repairs.

The ReSHEALience project created new recipes to build resilience into the structures. Crucially, these mixtures come from locally sourced materials. This is the only way to ensure that future buildings will be sustainable from the environmental perspective, Ferrara adds.

“In most cases, one of the largest impacts on the sustainability of materials is the transport,” he remarks. “For example, everybody says timber is sustainable, because we have the wood which is already there. But if I have to transport the timber from northern Italy to southern Italy, that is no longer sustainable,” Ferrara explains.The new mixtures mean that people can create concrete with greener cement, and also less of it. “Most of all, we are able to make concrete which allows us to build a structure using less concrete and which lasts longer,” he adds.

In order to make the construction industry more sustainable in the future, the entire supply chain must be considered, remarks Ferrara.

“So less CO2 to produce cement, less cement in concrete, less concrete in the structure. Which does not mean we have to sacrifice the performance,” he says. “So we are able to do all this for the same performance, and in most cases for better performance – which includes the durability of the structure.”

And that’s a mix that would have made ancient Roman architects proud.

Click here to find out more about Liberato Ferrara’s research: Next-generation concrete for more sustainable marine construction