The exact formula for Roman concrete has been lost. This is unfortunate, as many 2,000-year-old Roman concrete piers and breakwaters structures are even stronger today than they were when they were built millennia ago, while our modern marine concrete structures break down in decades. An international team of researchers recently discovered that seawater has a role to play in the ancient material’s surprising longevity.
Concrete in ancient Rome was comprised of volcanic ash, lime, and seawater, mixed with chunks of volcanic rock. A team led by University of Utah geologist Marie Jackson discovered it’s seawater that could help the building material last – the substance fosters the growth of interlocking minerals that provide cohesion to the concrete.
Back between 2002 and 2009 Jackson and colleagues found the rare mineral aluminous tobermorite, or Al-tobermorite, in Roman harbor concrete gathered by the ROMACONS project. The mineral is incredibly difficult to make in a laboratory, requiring high temperatures. Going back to those drill cores to scrutinize them with new methods for this research, Jackson found the mineral again along with a related one, phillipsite, in pumice particles and pores.
The team knew something had to encourage those minerals to grow in low temperatures after the concrete hardened, and it turns out seawater washing over those piers and breakwaters could be the key. Jackson said in a statement, “We’re looking at a system that thrives in open chemical exchange with seawater…No one has produced tobermorite at 20 degrees Celsius. Oh – except the Romans!”
Jackson has never come across the Roman recipe for concrete in an extensive search of old texts. But she’s working with geological engineer Tom Adams on a replacement recipe. The rocks the Romans used aren’t common throughout the world, so they’ll have to make substitutions. And if they’re successful, Roman concrete probably won’t start popping up everywhere, but could be perfect for certain projects like a proposed tidal lagoon for tidal power in the United Kingdom.
Jackson is the lead author on a study published on July 3 in American Mineralogist. She was joined by researchers at institutions in China, Italy, Washington, and California.