Ancient Romans created super strong concrete
By mixing aggregate with mineral-rich sea water
By Russel Davis
A recent study published in the journal American Mineralogist revealed the chemical structure that made ancient Roman concrete so durable that they remained strong for more than 1,500 years. To carry out the study, a team of researchers at the Department of Energy’s Lawrence Berkeley National Laboratory used X-rays to examine samples of Roman concrete taken from an ancient pier and breakwater site. The sample was analyzed at microscopic levels to determine what made it incredibly strong.
The research team found that the recipe for the ultra-durable concrete included a mix of volcanic ash, lime or calcium oxide, seawater, and lumps of volcanic rock. According to the experts, this recipe fortified ancient water-based structures that have become more enduring over the millennia. The research team’s previous work at the Berkeley Laboratory’s Advanced Light Source showed that the increased durability was a result of seawater reacting to the volcanic material in the concrete, which in turn allowed the formation of new materials that reinforced the ancient structures.
“At the ALS we map the mineral cement microstructures. We can identify the various minerals and the intriguingly complex sequences of crystallization at the micron scale…Contrary to the principles of modern cement-based concrete, the Romans created a rock-like concrete that thrives in open chemical exchange with seawater,” Marie Jackson, co-author and University of Utah geologist, told ScienceDaily.com.
Experts identify minerals that reinforce ancient structures
The analysis showed that calcium oxide particles used during the first stages of constructing the ancient structures may have reacted thoroughly with volcanic ash, which in turn resulted in the formation of aluminous tobermorite and phillipsite crystals. According to the researchers, the new set of minerals form fine fibers and plates that then filled up cracks and cavities in the structure. This in turn prevented cracks from growing, and made the ancient structures more durable over time. (Related: Ancient people used shockingly advanced mathematics to erect monuments based on sacred geometry.)
In contrast, most modern concrete is made from Portland cement that uses components — such as limestone, sandstone, ash, chalk, iron, and clay– that were otherwise not intended to chemically react. As a result, any chemical reaction may lead to unwanted damage and expansions in the concrete.
“I think [the research] opens up a completely new perspective for how concrete can be made – 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. There’s many applications but further work is needed to create those mixes. We’ve started but there is a lot of fine-tuning that needs to happen. The challenge is to develop methods that use common volcanic products – and that is actually what we are doing right now,” Jackson said in a separate article on The Guardian website.
Why Roman concrete still stands strong while modern version decays
Scientists have cracked the secret to Roman water-based structures’ strength – and findings could help today’s builders
Their structures are still standing more than 1,500 years after the last centurion snuffed it: now the Romans’ secret of durable marine concrete has finally been cracked.
The Roman recipe – a mix of volcanic ash, lime (calcium oxide), seawater and lumps of volcanic rock – held together piers, breakwaters and harbours. Moreover, in contrast to modern materials, the ancient water-based structures became stronger over time.
Scientists say this is the result of seawater reacting with the volcanic material in the cement and creating new minerals that reinforced the concrete.
The ancient Romans had a recipe for concrete that won't corrode in seawater. Scientists are trying to figure it out. Learn more at https://unews.utah.edu/roman-concrete/
“They spent a tremendous amount of work [on developing] this – they were very, very intelligent people,” said Marie Jackson, a geologist at the University of Utah and co-author of a study into Roman structures.
As the authors note, the Romans were aware of the virtues of their concrete, with Pliny the Elder waxing lyrical in his Natural History that it is “impregnable to the waves and every day stronger”.
Now, they say, they’ve worked out why. Writing in the journal American Mineralogist, Jackson and colleagues describe how they analysed concrete cores from Roman piers, breakwaters and harbours.
Previous work had revealed lime particles within the cores that surprisingly contained the mineral aluminous tobermorite – a rare substance that is hard to make.
The mineral, said Jackson, formed early in the history of the concrete, as the lime, seawater and volcanic ash of the mortar reacted together in a way that generated heat.
But now Jackson and the team have made another discovery. “I went back to the concrete and found abundant tobermorite growing through the fabric of the concrete, often in association with phillipsite [another mineral],” she said.
She said this revealed another process that was also at play. Over time, seawater that seeped through the concrete dissolved the volcanic crystals and glasses, with aluminous tobermorite and phillipsite crystallising in their place.
These minerals, say the authors, helped to reinforce the concrete, preventing cracks from growing, with structures becoming stronger over time as the minerals grew.
By contrast, modern concrete, based on Portland cement, is not supposed to change after it hardens – meaning any reactions with the material cause damage.
Jackson said: “I think [the research] opens up a completely new perspective for how concrete can be made – 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.”
The findings offer clues for a concrete recipe that does not rely on the high temperatures and carbon dioxide production of modern cement, but also providing a blueprint for a durable construction material for use in marine environments. Jackson has previously argued Roman concrete should be used to build the seawall for the Swansea lagoon.
“There’s many applications but further work is needed to create those mixes. We’ve started but there is a lot of fine-tuning that needs to happen,” said Jackson. “The challenge is to develop methods that use common volcanic products – and that is actually what we are doing right now.”