Roman concrete produces as much, if not more, CO2 as modern concrete, fewer air pollutants.

Builders in ancient Rome used a special kind of ancient concrete to construct their aqueducts, bridges, and buildings. But is Roman concrete more sustainable than the Portland cement used in today's concrete? The answer is more nuanced than one might think, according to a new paper published in the journal iScience. Roman concrete produces as much CO2 as modern methods, but fewer air pollutants.

As we've reported previously, like today's Portland cement (a basic ingredient of modern concrete), ancient Roman concrete was basically a mix of a semi-liquid mortar and aggregate. Portland cement is typically made by heating limestone and clay (as well as sandstone, ash, chalk, and iron) in a kiln. The resulting clinker is then ground into a fine powder, with just a touch of added gypsum—the better to achieve a smooth, flat surface. But the aggregate used to make Roman concrete was made up of fist-sized pieces of stone or bricks.

...read more at arstechnica.com