How Roman concrete could build better buildings now
Long regarded for a far more durable product, the 2,000-year-old recipe is also better environmentally than current processes.
Here's a nerdy but exciting story that combines archeology, chemistry and infrastructure issues -- and it has an economic impact, too.
A team of international researchers say they've uncovered the chemical secrets of why 2,000-year-old Roman concrete has lasted so long, especially in breakwaters along some of the ancient empire's ports, compared with the modern recipe for concrete, which includes portland cement. And unlocking that secret, they say, may have long-term environmental benefits as well as help future building projects.
"It's not that modern concrete isn't good -- it's so good we use 19 billion tons of it a year," Paulo Monteiro with the U.S. Department of Energy's Lawrence Berkeley National Laboratory said in a press statement earlier this month. "The problem is that manufacturing portland cement accounts for 7% of the carbon dioxide that industry puts into the air."
Monteiro led the research team, which analyzed concrete samples taken from a submerged Roman breakwater in the Mediterranean Sea. The secret to its durability, they found, was a combination of limestone (heated and powdered into lime), volcanic rock and seawater. As the press statement noted, the Romans mixed the lime and volcanic ash into a mortar. They added volcanic tuff -- the rocks formed by explosive volcanic eruptions -- to the mortar and then packed the whole mixture into wood forms and submerged them.
"The seawater instantly triggered a hot chemical reaction," the press release said. "The lime was hydrated -- incorporating water molecules into its structure -- and reacted with the ash to cement the whole mixture together."
And even when seawater wasn't available, the Roman method used much less lime and lower baking temperatures than modern concrete. Researchers say along with cutting greenhouse emissions, adapting the Roman method could provide the world with a more durable concrete.
"In the middle 20th century, concrete structures were designed to last 50 years, and a lot of them are on borrowed time," Monteiro said. "Now we design buildings to last 100 to 120 years."
"The question remains: Can we translate the principles from ancient Rome to the production of modern concrete?" Marie Jackson, a research engineer at the University of California at Berkeley and part of the research team, told Bloomberg. "I think that is what is so exciting about this new area of research."
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