We’ve long known that Romans knew how to make highly durable concrete structures. After all, many of their concrete structures, like the Parthenon, are still standing. The Pantheon was built 2,000 years ago and its roof is still the world’s largest unreinforced concrete dome.

ABC News in Australia has posted that scientists have finally discovered how they did it. Here’s some of what it says:

So how has Roman concrete outlasted the empire, while modern concrete mixtures erode within decades of being exposed to seawater?

Scientists have uncovered the chemistry behind how Roman sea walls and harbour piers resisted the elements, and what modern engineers could learn from it.

Romans built their sea walls from a mixture of lime (calcium oxide), volcanic rocks and volcanic ash, a study, published in the journal American Mineralogist, found.

Elements within the volcanic material reacted with sea water to strengthen the concrete structure and prevent cracks from growing over time.

So how does it work?

Scientists previously discovered Roman concrete contained aluminous tobermorite, a rare mineral that is hard to produce.

The tobermorite formed within the Roman concrete early on, as seawater reacted with the mixture to generate heat.

Now a more detailed examination of the chemistry of the concrete showed significant amounts of that rare mineral growing out of another mineral naturally found in volcanic rock called phillipsite.

The long-term exposure of the concrete to seawater caused both the tobermorite and phillipsite to crystallise throughout the concrete.

These prevented cracks from forming, therefore reinforcing the concrete over time.

The researchers said this could lead to more environmentally friendly ways of modern concrete construction, but warned it may take years before the precise Roman mixture was discovered.

“I think [the research] opens up a completely new perspective for how concrete can be made,” Dr Jackson said.

“That what we consider corrosion processes can actually produce extremely beneficial mineral cement and lead to continued resilience, in fact, enhanced perhaps resilience over time.”

Photo: Ancient Roman concrete harbors and the project’s drill sites, as indicated by the green circles. Volcanic districts are indicated by red triangles. Photo courtesy Marie Jackson et al