Concrete from ancient Rome is just as strong as modern concrete, the ancient material may be more resilient to wear than modern mixtures, and it is better for the environment.
Every year, 19 billion tons of concrete is used in construction, making it one of the most popular building materials in the world. But heating the limestone (calcium carbonate) and clay to needed to create cement for the manufacture of concrete generates carbon emissions equal to seven percent of all industrial CO2 released into the atmosphere. The greenhouse gas comes both from the heating of the material as well as from the limestone itself.
Paulo Monteiro, a researcher from the Lawrence Berkeley National Laboratory, believes that the "sea concrete" used by ancient Romans in the construction of seaports and facilities could be the answer to reducing those emissions. The Roman concrete mix, made with volcanic ash and 10 percent limestone, only has to be heated to 1,650 degrees Fahrenheit, about 1,000 degrees lower than a typical modern variety, usually Portland cement.
"Volcanic ash is available in a good deal of the world, usually there are entire mountains of it following a volcanic eruption. The Romans were unbelievably good at using it as a building material," Monteiro said.
The ancient Romans would begin the manufacture of their waterproof concrete by mixing volcanic ash and limestone into a mortar, then adding small pieces of volcanic stones. The material would then be placed into wooden vessels, and placed in seawater. This would quickly create a reaction with the limestone, heating the substance, causing the mixture to fuse together. This secret Roman technology was first publicized by Marcus Vitruvius Pollio, a Roman engineer, in the year A.D. 30.
The ancient construction compound formed a solid binding agent that added durability to the material. This mixture, calcium-aluminum-silicate-hydrate or C-A-S-H, contains aluminum and less silicon than modern Portland cement, which is comprised of calcium, silica and hydrates.
An ancient breakwater in Pozzuoilli Bay, west of Naples, gave Monteiro a chance to see up-close how well the Roman concrete from which it was constructed has withstood the test of time.
"In the middle 20th century, concrete structures were designed to last 50 years. Now we design buildings to last 100 to 120 years. Yet, the Roman concrete has survived 2,000 years of waves and chemical attack," Monteiro said.
Studying the material in depth, Monteiro and his team determined that concrete from ancient Rome possesses just as much strength as modern types of concrete.
A type of volcanic ash used in ancient Rome called Pozzolan, common throughout the world, could replace 40 percent of the world's use of Portland cement, according to Monteiro.