The Green Concrete of Ancient Rome

Cement is one of the most energy-intensive materials to produce, so reducing its CO2 footprint could make a significant difference in the climate change equation. In “Cementing the Future” (Winter 2011), Eli Kintisch described how Stanford geologist Brent Constantz was looking to nature—specifically, the way marine organisms create carbonate shells—to develop a carbon-negative cement.

Other scientists are now looking to history for recipes for a more environmentally sound cement. Researchers from the University of California, Berkeley, analyzed the microscopic structure, chemical composition, and mechanical properties of the crystalline cementing component of ancient Roman concrete—a material that has survived 2,000 years, submerged in the Mediterranean Sea. The team recently published its results in Journal of the American Ceramic Society.

To make Portland cement, a mix of limestone and clays must be heated to 1,450 degrees Celsius. The Roman seawater concrete, by contrast, used lime mixed with volcanic ash, and the calcination of limestone occurs at about 900 degrees Celsius—requiring far less fuel to produce than Portland cement does. And the Roman concrete has withstood the test of time: the mixture of lime and ash from nearby volcanoes reacts with seawater to form an extremely strong and stable material. This recipe could provide a model for producing durable, environmentally friendly concretes, say the researchers, since volcanic ash is found in many areas of the world.

Jackson, M.D. et al. 2013. Journal of the American Ceramic Society doi: 10.1111/jace.12407.

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