Cracking the Secrets of Ancient Rome’s High Performance Concrete

Sometimes the biggest innovations come from analyzing the past.

In the modern world, concrete is one of the most important building components due to its strength, utility and perceived durability. Concrete made from Portland cement – the most common form in wide use – has an estimated useful life of 100 years. While that may seem like a long time, it begs the question: How come the concrete in ancient Rome lasted so long?

Researchers led by Berkely Lab’s Paulo Monteiro studied core samples of 2,000 year-old Roman concrete structures, especially those used in marine environments. (Portland cement is expected to have a useful life of less than 50 years in such conditions.) Their findings may lead to more durable and substantially more environmentally friendly concrete.

“It’s not that modern concrete isn’t good – it’s so good we use 19 billion tons of it a year,” says Monteiro. “The problem is that manufacturing Portland cement accounts for seven percent of the carbon dioxide that industry puts into the air.”

The Ancient Roman Secret to Long Lasting Concrete: Volcanic Rock/Ash

For land-based applications, the ancient Romans mixed lime and volcanic rock. Underwater applications utilized lime mixed with volcanic ash. Wooden forms were filled with mortar made from the lime and ash. Upon contact with seawater, a hot chemical reaction transformed the mixture into some of the most durable concrete the world has ever known.

The research also showed that the overall environmental impact of making the volcanic concrete is much less than our current methods. According to Berkely Lab:

Portland cement is the source of the “glue” that holds most modern concrete together. But making it releases carbon from burning fuel, needed to heat a mix of limestone and clays to 1,450 degrees Celsius (2,642 degrees Fahrenheit) – and from the heated limestone (calcium carbonate) itself. Monteiro’s team found that the Romans, by contrast, used much less lime and made it from limestone baked at 900˚ C (1,652˚ F) or lower, requiring far less fuel than Portland cement.

The primary chemical elements that make up the “glue” in Portland cement are calcium, silicates and hydrates (C-S-H). The Roman binder based on so-called pozzolan ash is slightly different: calcium, aluminum, silicates and hydrates (C-A-S-H).

“For us, pozzolan is important for its practical applications,” says Monteiro. “It could replace 40 percent of the world’s demand for Portland cement. And there are sources of pozzolan all over the world. Saudi Arabia doesn’t have any fly ash, but it has mountains of pozzolan.”

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.

Via Berkely Lab

Image courtesy Oggie Dog