Secrets of Ancient Roman concrete revealed
By Janet Fang, Businessweek, June 18, 2013
The Ancient Romans were master engineers. Now, 2,000 years later, scientists have figured out the secret behind the creation of Roman concrete—one of the world’s most durable man-made creations ever. The discovery may impact how we build cities of the future. Bloomberg Businessweek reports.
Roman harbors have always fascinated geologists and engineers. Breakwaters constructed out of Roman concrete are still perfectly intact despite constant pounding by the sea.
The most common blend of modern concrete—Portland cement, used for 200 years—doesn’t come close to matching that track record. In seawater, its service life is less than 50 years. “The building industry has been searching for a way to make more durable concretes,” says Marie Jackson from the University of California, Berkeley.
So, an international team of researchers analyzed the mineral components of a concrete breakwater sample dating back to 37 B.C., extracted from the floor of Pozzuoili Bay.
The secret to the lost recipe of superior Roman concrete lies in its unique mineral formulation and production technique. According to a Lawrence Berkeley National Laboratory press release:
The Romans made concrete by mixing lime and volcanic rock. For underwater structures, lime and volcanic ash were mixed to form mortar, and this mortar and volcanic tuff were packed into wooden forms. The seawater instantly triggered a hot chemical reaction. The lime was hydrated—incorporating water molecules into its structure—and reacted with the ash to cement the whole mixture together.
Concrete made with Portland cement lacks the lime-and-ash mixture that made the Roman formula an exceptionally stable binder.
The work also points to how less environmentally damaging the Roman concrete is. Manufacturing Portland cement accounts for 7 percent of the carbon dioxide that industry puts into the air. The Romans used much less lime and made it from limestone baked at a much lower temperature, requiring far less fuel.