Modern scientists have known for quite some time that Roman concrete was very different from the Portland concrete used in construction work today. But the chemistry behind the process that made the concrete so durable and resistant to seawater has always been a mystery.
However, scientists working at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) used X-rays to study samples of Roman concrete from an ancient pier and breakwater sites to learn more about the mineral makeup of the cement, reports Science Daily.
We do know the Roman recipe for their concrete was a mixture of volcanic ash, lime (calcium carbonate), seawater and lumps of volcanic rock. What is astounding about this mixture is that it gets stronger over time. The researchers found out that this happened as a result of seawater reacting with the volcanic material in the cement, creating new minerals.
“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. Writing in the journal American Mineralogist, Jackson and her colleagues explain how they analyzed the concrete core samples.
Explaining the makeup of Pozzolana concrete
Previous research into the makeup of the unusual concrete called Pozzolana concrete, found that it contained a rare mineral called aluminous tobermorite, a layered mineral that played a key role in strengthening the concrete as it aged over time. The mineral was formed by the heat produced as seawater, lime and volcanic ash reacted with each other.
But the scientists discovered something else about the concrete – “I went back to the concrete and found abundant tobermorite growing through the fabric of the concrete, often in association with phillipsite [another mineral],” Jackson said.
The Guardian reports that the study suggests that over a long period of time, the seawater seeped through the concrete, dissolving the volcanic ash and glasses, allowing for aluminous tobermorite and phillipsite crystals to fill up the spaces. And as the crystals grew, they reinforced the concrete, preventing cracks from growing and basically, making the structures stronger.
Our modern cement, based on Portland concrete, is not supposed to change as it gets hard, so it goes without saying that any chemical reactions, especially with seawater will cause damage.
Jackson said: “I think [the research] opens up a completely new perspective on 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.”
Modern concrete and its environmental impact
As the BBC explains, modern buildings are constructed using concrete based on Portland cement. Portland cement is produced by heating limestone, sandstone, ash, chalk, iron, and clay in a kiln to form something called clinker, then grinding the clinker, and adding small amounts of other materials, such as one or more of the forms of calcium sulfate.
The process of making the cement generates over 5.0 percent of the world’s greenhouse gasses, and additionally, it is a caustic mixture that can cause burns. In some instances, severe exposure can lead to lung cancer. And Portland cement can contain some hazardous components; such as crystalline silica and hexavalent chromium.
Basically, having a greater understanding of the Roman concrete recipe could possibly lead to greener building technologies in today’s world. As a matter of Fact, Dr. Jackson told the BBC earlier this year that the planned Swansea tidal lagoon should be built using the ancient Roman knowledge of concrete.
“Their technique was based on building very massive structures that are really quite environmentally sustainable and very long-lasting,” she said, adding, “I think Roman concrete or a type of it would be a very good choice [for Swansea]. That project is going to require 120 years of service life to amortize [pay back] the investment.
