Modern concrete is a mix of a lime-based cement, water, sand and so-called aggregates such as fine gravel. The formula for Roman concrete also starts with limestone: builders burned it to produce quicklime and then added water to create a paste. Next they mixed in volcanic ash—usually three parts volcanic ash to one part lime, according to the writings of Vitruvius, a first-century B.C. architect and engineer. The volcanic ash reacted with the lime paste to create a durable mortar that was combined with fist-size chunks of bricks or volcanic rocks called tuff, and then packed into place to form structures like walls or vaults.
Monday, December 5, 2011
I know you've always wanted to know, so here is how the Romans made that concrete that keeps their buildings standing after 2,000 years: