Roman architecture has been known to last for thousands of years and get stronger with each passing year. No one knew the reason behind it, but new research has now revealed the chemical processes that are behind the super strength of these buildings.
A research team under the lead of Marie D. Jackson from the University of California at Berkeley has been on the case of these amazing structures. Back in 2014, their first study revealed the recipe for Roman concrete, which was a mixture of lime, volcanic ash, and seawater along with a volcanic rock aggregate that created super-strong concrete holding these buildings together.
But a follow-up study, published in American Mineralogist, now also reveals another previously hidden factor at play behind the super strong concrete. The paper suggests that the strengthening process was facilitated by a steady filtering of corrosive and salty sea water through the concrete over the years, that grew rare, interlocking minerals, which helps the concrete grow stronger as the years go by.
The Romans created concrete inspired by naturally-cemented volcanic ash deposits using a pozzolanic reaction that grows minerals between the aggregate and the mortar, which, in the case of Romans, was a mixture of silica oxides and lime in the volcanic ash that prevents the cracks from growing. This is facilitated by the presence of a rare mineral called aluminous tobermorite, which helps mineral crystals grow around the lime particles. But it only happens at high temperatures, so the modern day researchers were still at loss about how the Romans managed to pull this off.
But now Marie D. Jackson’s team conclude that it was in fact, a heavy dose of seawater that helped the reaction be so effective. The seawater seeps through the material and dissolves the components of the volcanic ash, which over the course of 2000 years has allowed minerals to grow from the alkaline fluids leeching out of the construction. This leads to the proliferation of interlocking and creation of crystal-shaped structures increasing the concrete’s resistance to brittle fracture.
“We’re looking at a system that’s contrary to everything one would not want in cement-based concrete,” said Jackson in a press release. “We’re looking at a system that thrives in open chemical exchange with seawater.”
So why don’t we apply the same principles in our construction today?
“Romans were fortunate in the type of rock they had to work with,” said Jackson. “They observed that volcanic ash grew cements to produce the [mortar]. We don’t have those rocks in a lot of the world, so there would have to be substitutions made.”
Jackson and his team are now working to reproduce the replacement recipe, which if fully developed, it can revolutionize modern day construction materials.