An international team of researchers from the US Department of Energy’s Lawrence Berkeley National Laboratory have uncovered the chemical mysteries of a concrete Roman breakwater submerged for over 2000 years in the Mediterranean Sea.
The researchers discovered that the ancient Roman concrete that is superior to the majority of modern concrete because they mixed 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 water immediately caused 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.
Portland cement is responsible for the adhesive property that holds most modern concrete together, but manufacturing it releases carbon from burning fuel, needed to heat a mix of limestone and clays to 2,642˚ Fahrenheit, and from the heated limestone, or calcium carbonate, itself. The Romans, however, used far less lime and made it from limestone baked at 1,652˚ Fahrenheit, a far lower temperature requiring far less fuel that Portland cement.
Modern concrete that is more sustainable includes volcanic ash or fly ash from coal-burning power plants. Taking a cue from the Romans, if modern concrete is made with less fuel, thereby releasing less carbon into the atmosphere, it will be much more environmentally friendly.