Why Roman Concrete has Survived for Centuries

Concrete, in one form or another, has been used throughout time starting with some of the earliest civilizations. While we are all familiar with the impressive architectural structures from ancient Roman times, one mystery that intrigues people today is why the buildings’ concrete lasted so long.  In contrast, modern concrete has a lifespan of about 120 years, not 2,000 years.  

We have known that ancient Roman concrete was made from volcanic sand and mortar, but recently, researchers went one step further to discover why the concrete has survived for so many years.  According to the new study reported on the Ancient-Origins’ website, a group of engineers and researchers mixed up a batch of mortar using a recipe from the ancient Roman architect, Vitruvius.  The mortar was left to harden for six months before it was examined. 

Studying the mortar under microscopes, researchers discovered that clusters of a dense mineral had formed during the Roman process.  They explain that the “strätlingite crystals, formed by the volcanic sand as it binds with limestone, prevented the spread of cracks by reinforcing interfacial zones,” further adding that “interfacial zones are weak links inside the concrete.”

Roman builders discovered that Pozzolonic ash from the Alban Hills’ Pozzolane Rosse ash flow created the best mortar.  In fact Augustus, the first Roman emperor, decreed in 27 A.D. that Pozzolonic ash be the standard used in Roman buildings.  With the benefit of these materials, the Romans built numerous architectural wonders including the Pantheon entirely from concrete and without using reinforcing steel such as we do today.  

Furthermore, the concrete manufactured by the Romans was more environmentally friendly as it only needed to be heated to 900 degrees Celsius as opposed to today’s concrete that must be heated to 1,450 degrees.  Ancient-Origins speculated in 2013 that, “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.”  

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Sources:pnas.org/content/111/52/18484.abstract, history.com/news/the-secrets-of-ancient-roman-concrete, ancient-origins.net/news-history-archaeology/researchers-discover-secret-recipe-roman-concrete-020141