Sunday, February 5, 2023

Scientists uncover secret to longevity of Roman buildings

(CNN) — The majestic structures of ancient Rome have survived through the millennia, testament to the skill of Roman engineers, who perfected the use of concrete.

But how did its building material help giant buildings like the Pantheon (which has the largest unreinforced dome in the world) and the Colosseum stand for more than 2,000 years?

In many cases, Roman concrete has proven to be more durable than its modern equivalent, which can deteriorate in a matter of decades. Now, scientists responsible for a new study claim to have discovered the mysterious ingredient that allowed the Romans to make their building materials so durable and to build elaborate structures in difficult places such as docks, sewers and seismic zones.

The study team, made up of researchers from the United States, Italy and Switzerland, analyzed samples of 2,000-year-old concrete taken from a wall at the Privernum archaeological site in central Italy, and other samples similar in composition. The Roman Empire.

The researchers found that the white pieces of concrete, called lime clasts, gave it the ability to heal cracks that build up over time. White bits were previously ignored as evidence of sloppy mixing or poor quality raw materials.

“It was very hard for me to believe that the ancient Romans[engineers]didn’t do a good job, because they put a lot of effort into selecting and processing materials,” says Admir Macic, study author and associate professor of civil engineering. and environmental engineering. at the Massachusetts Institute of Technology.

“Scholars wrote down precise recipes and superimposed them on works (from across the Roman Empire),” Messick said.

The new discovery could help make today’s concrete construction more durable, potentially revolutionizing society as the Romans did in their own time.

“Concrete allowed the Romans an architectural revolution,” explains Messick. “The Romans were able to build cities and make them something extraordinary and beautiful to live in. And that revolution basically completely changed the way humans lived.”

Roman Concrete

Tourists visit the Colosseum in Rome in June 2019. credit: Eyeswide Open / Getty Images

Durability of lime clast and concrete

Concrete is essentially artificial stone or rock, formed by mixing cement, a binding agent usually composed of limestone, water, fine aggregate (sand or finely crushed rock), and coarse aggregate (gravel or crushed rock) .

Messick noted that Roman texts suggested the use of slaked lime (when the lime is mixed with water before it is first mixed) as a binder, and so scholars have assumed that Roman concrete was made is made.

Upon further study, researchers concluded that lime explosions were due to the use of quicklime (calcium oxide) – the most reactive and dangerous dry form of limestone – in mixing concrete, in place of the use of dead lime, or in its Excessive.

Further analysis of the concrete showed that lime flakes at the extreme temperatures predicted by the use of quicklime, and that this “hot mix” was critical to the concrete’s durable nature.

“The benefits of hot mixing are two-fold,” Messick says in a press release. “First, when finished concrete is heated to a high temperature, it allows chemistry that would not be possible if only dead lime was used, which produces compounds associated with high temperatures. which otherwise would not have happened.

Second, this increase in temperature significantly reduces curing and setting times, as all reactions are accelerated, allowing for much faster fabrication.”

To test whether blasts of lime were responsible for Roman concrete’s apparent ability to repair itself, the team conducted an experiment.

He made two concrete models, one according to Roman formulas and the other according to modern standards, and deliberately broke them. After two weeks, water could no longer flow through concrete made with the Roman recipe, while it passed without problem through a piece of concrete prepared without lime.

Their findings suggest that lime flakes can dissolve in cracks and recrystallize when exposed to water, healing cracked cracks before they spread. According to the researchers, this self-healing ability could pave the way for the production of more durable and therefore more durable modern concrete. According to the study, this will reduce the carbon footprint of concrete, which accounts for up to 8% of global greenhouse gas emissions.

For many years, researchers thought that volcanic ash from the Pozzuoli area in the Bay of Naples was what made Roman concrete so strong. This type of ash was transported throughout the vast Roman Empire for use in construction, and was described in the accounts of architects and historians of the time as a key ingredient in concrete.

Both components are important, according to Messick, but lime has been overlooked in the past.

The research was published in the academic journal Science Advances.

Nation World News Desk
Nation World News Desk
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