About 2000 years ago, the Romans developed a standard formula for a volcanic ash-lime mortar that was used to bind cobble-sized fragments of tuff and brick in the concrete walls of a number of ancient architectural monuments.
In order to determine how modern concrete structures could achieve the longevity of renowned Roman landmarks such as the Pantheon, Trajan’s Markets and the Colosseum, researchers reproduced the formula and cured it over 180 days while observing its mineralogical changes.
The researchers found that the curing process resulted in the formation of a calcium-alumino-silicate mineral. A press release from one of the universities that led the study, California-based UC Berkeley, explained that this durable mineral “acts to bind and reinforce interfacial zones in the mortar, preventing obstacles to the growth of micro-cracks”.
Marie Jackson, a faculty scientist from UC Berkeley’s Department of Civil and Environmental Engineering, stated that in addition to “unmatched resilience and durability”, these Roman mortars offered environmental advantages.
According to Jackson, the process of manufacturing Portland cement – which is used to bind most modern concrete – accounted for about seven per cent of the total annual amount of carbon emitted.
“Roman architectural mortar, by contrast, is a mixture of about 85 per cent volcanic ash, fresh water and lime, which is calcined at a much lower temperature than Portland cement,” she explained. “Coarse chunks of volcanic tuff and brick compose about 45 to 55 per cent of the concrete. The result is a significant reduction in carbon emissions.
“If we can find ways to incorporate a substantial volumetric component of volcanic rock in the production of specialty concretes, we could greatly reduce the carbon emissions associated with their production and also improve their durability and mechanical resistance over time,” Jackson concluded.
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Doing concrete as the Romans did