“It’s the most durable building material in human history,” said Philip Brune, a researcher at DuPont, “and I say that as an engineer not prone to hyperbole.”
As reported in the Washington Post and Popular Mechanics, the newly rediscovered recipe for ancient Roman concrete could help in the battle against rising sea levels.
As global temperatures rise, sea ice is melting and causeing the sea level to rise at a faster rate than during the 1900s, says Popular Mechanics. “Exactly how much it will rise is dependent on a number of variables, but there is a high likelihood that rising sea levels will force us to reinforce infrastructure around coastal cities.”
While sea walls exist all around the world, from Britain to Australia to Japan, they inevitably get pounded by the tides into dust. However, as modern concrete structures have shown weakness even in the last few hundred years, ancient Roman concrete has stood the test of millennia.
The material, called opus caementicium by the Romans, is made from a hydraulic cement, meaning it can set underwater, or in wet conditions. The Romans mixed this with volcanic ash, which added a mineral called phillipsite, a study published in American Mineralogist reported. They found that aluminous tobermorite crystals grow in the Roman concrete when it comes into contact with water. They believe these crystals provide the structural reinforcement that makes Roman concrete so durable.
Pliny the Elder, a famed Roman author and historian, wrote “As soon as it comes into contact with the waves of the sea and is submerged [it] becomes impregnable to the waves.”
Between 22 and 10 BCE, the Romans constructed an underwater foundation for the harbor at Caesarea (which is now part of Israel). Two thousand years later, that foundation remains firm and intact. Rather than eroding the concrete, the saltwater actually strengthens it.
An archaeologist from the University of Utah, Marie Jackson, is attempting to recreate this cement using volcanic rocks found around San Francisco. She has found that artificially producing the aluminous tobermorite requires a large amount of heat, and it would probably be more cost effective to harvest it at the source—volcanos—rather than create it artificially.
Despite that, it remains a positive alternative to the steel-reinforced sea walls being built today. And if ocean levels are to rise as scientists predict, alternatives like this could be essential.
As a test case, Jackson proposed the concrete for a U-shaped breakwater in the UK, where they want to use the movement of the waves as a new source of electricity. Jackson says that it would take 120 years to break even on the money spent on the project, and in that time standard cement will have likely broken down. Instead, she recommends this Roman concrete, shown to last for thousands of years. Time will tell if she can properly recreate the recipe.