The longevity of ancient Roman structures lies in unslaked lime, scientists claim

Washington/Rome - The longevity of ancient Roman structures lies in a specific method of making concrete and mortar. This was shown by research from scientists at the Massachusetts Institute of Technology (MIT), Harvard University, and research centers in Italy and Switzerland, writes the newspaper Le Monde. Through the analysis of ancient Roman building materials, the researchers concluded that the key element in the buildings' resistance to the ravages of time is the use of slaked lime. This allows the mortar and concrete to acquire "self-healing properties."

According to the authors of the study, ancient Roman buildings exhibit very good resistance to wear. This is evidenced by structures such as the Roman Pantheon, built in the second century, or some aqueducts, whose structures are still in use. According to the authors, this contrasts with Portland cement, which predominates today and has a reported lifespan of 100 years.

For a long time, scientists attributed the good qualities of ancient Roman buildings to the use of pozzolana and volcanic ash in the production of concrete and mortar in ancient Rome. Today, sand is most commonly used.

However, according to the authors, this is not a complete explanation. In analyzing ancient Roman mortars and concretes, they noticed that they contain large particles of limestone, known as clasts. Previous studies attributed this to poor mixing technology. "The notion that the presence of these lime clasts can be easily explained by low-quality control has always annoyed me," said one of the study's authors, Admir Masic from MIT.

More detailed analyses also showed that the particles have a structure that corresponds to having formed at high temperatures. This would disprove the hypothesis that the particles arose from inconsistent mixing technology. The researchers explain their findings by suggesting that slaked lime was indeed used in the production of mortar and concrete in ancient Rome, which triggers chemical reactions that create high temperatures. Due to the specific structure of the clasts, ancient Roman concrete, according to the researchers, has self-healing capabilities.

The researchers verified this in a laboratory experiment. They made a small crack in concrete produced using both ancient Roman and modern methods, into which they then poured water. After two weeks, the concrete produced using the ancient Roman method was able to seal the gap, which did not happen with the concrete produced using modern methods.

The discovery, according to the study, could be interesting for the development of new types of concrete and ecology. According to estimates, the production of concrete and building materials accounts for about eight percent of global greenhouse gas emissions. Producing a material that decays more slowly could lead to a reduction in emissions in this sector.