Scientists studying the composition of Roman concrete , which has been submerged under the Mediterranean Sea for the last 2,000 years, have discovered that it was superior to modern-day concrete in terms of durability and being less environmentally damaging.
The international team of researchers led by the US Department of Energy’s Lawrence Berkeley National Laboratory made the discovery while examining concrete samples recovered from the Harbour of Baiae, one of the many ancient underwater sites in the northwestern region of the Bay of Naples.
The Romans made concrete by mixing lime and volcanic rock. For underwater structures, the combination of lime and volcanic ash with seawater instantly triggered a chemical reaction in which the lime incorporated molecules into its structure and reacted with the ash to cement the whole mixture together.
The team of researchers found that Roman concrete differs from the modern kind in several essential ways. One is the kind of glue that binds the concrete’s components together. Roman concrete produces a significantly different compound to modern day Portland cement, which is an incredibly stable binder. The second concerns the hydration products in concrete – the ancient seawater concrete contains the ideal crystalline structure of Tobermorite, which has a greater strength and durability than the modern equivalent.
“In the middle 20th century, concrete structures were designed to last 50 years, and a lot of them are on borrowed time,” research lead Paulo Monteiro said. “Now we design buildings to last 100 to 120 years.” Yet Roman harbour installations have survived 2,000 years of chemical attack and wave action underwater.
Finally, microscopic studies identified other minerals in the ancient concrete which show potential application for high-performance concretes, including the encapsulation of hazardous wastes.
The results of the study show how these improvements could be adopted in the modern world and, in particular, how they could result in a significant reduction of environmental damage caused by the manufacturing of concrete.
“It’s not that modern concrete isn’t good — it’s so good we use 19 billion tons of it a year,” said Monteiro. “The problem is that manufacturing Portland cement accounts for seven percent of the carbon dioxide that industry puts into the air.”
Conventional modern cement requires heating a mix of limestone and clay to 1,450 degrees Celsius which releases significant amounts of carbon into the atmosphere. In contrast, Roman cement used much less lime and made it from baking limestone at 900 degrees Celsius, requiring much less fuel.
Stronger, longer-lasting modern concrete, made with less fuel and less release of carbon into the atmosphere, may be the legacy of a deeper understanding of how the Romans made their incomparable concrete. Another significant lesson from this study is that our ancient ancestors were not as primitive as many believe. In fact, many would argue that certain aspects of their knowledge were significantly more advanced than our own.