Scientists solve the mystery of why ancient Roman buildings lasted longer – CNN.co.jp

2023.04.09 Posted on Sun at 17:30 JST

Katie Hunt, CNN

The magnificent structures of ancient Rome have been around for thousands of years. This is evidence of the ingenuity of the ancient Roman engineers who perfected the use of concrete.

But how did the building materials they used help keep gigantic structures like the Pantheon (which contains one of the world’s largest unsupported domes) and the Colosseum alive for more than 2,000 years?

Ancient Roman concrete, called “Roman concrete,” has often been shown to last longer than modern concrete. Modern concrete can deteriorate in a matter of decades. How were the ancient Romans able to make building materials long-lasting and build complex structures in hard-to-build places like sidewalks, sewers, and seismic zones? Scientists conducting some of the latest research claim to have finally discovered the mysterious substance that made it possible.

The research team, which also includes researchers from the United States, Italy and Switzerland, analyzed 2,000-year-old concrete samples taken from the walls of the Priverno ruins in central Italy. This specimen is similar in formulation to other types of concrete found throughout the Roman Empire.

Researchers have found that the white lumps in concrete, called “lime crust,” give concrete the ability to repair cracks that develop over time. Until then, these white lumps were overlooked as a sign of poor mixing or poor quality ingredients.

said Massachusetts Institute of Technology (MIT) civil engineer Admir Masik, assistant professor of environmental engineering and author of the study.

Macyck added: “Scientists wrote[الرومان القدماء]Exactly how to make[الخرسانة]Then they imposed it on construction sites[في جميع أنحاء الإمبراطورية الرومانية]”.

This new discovery could help make today’s concrete more sustainable, and could even reshape society as the Romans did.

“Concrete enabled the Romans to revolutionize architecture,” Masek said, adding, “(Thanks to concrete) the Romans were able to build many cities and turn them into beautiful and wonderful living environments.” This revolution has changed the way people live,” he added.

Durability of lime and concrete veneer

Concrete is basically an artificial stone or rock made by mixing cement, which generally consists of limestone, water, fine aggregate (sand or crushed rock) and coarse aggregate (gravel or crushed stone).

Ancient Roman texts suggested that slaked lime (lime mixed with water and age) was used in cement. So the scientists thought Roman concrete was made with this slaked lime as the main ingredient, says Massick.

However, more research revealed that the cause of lime crust in Roman concrete was that quicklime (also known as calcium oxide, which is highly reactive), the researchers concluded that this was due to the use of dry, hazardous limestone.

In addition, as a result of further analysis of the concrete, the lime crust formed under extremely high temperatures, which is believed to be generated using quicklime, and “hot mixing (a method of making concrete under extremely high temperatures)” increases the durability of the concrete and turns out to be the key to the improvement .

“There are two advantages to hot mixing,” Masek said in a press release. “First, heating the whole concrete to high temperatures allows chemical reactions that would not occur if only slaked lime were used, resulting in high-temperature bound compounds that could not otherwise form. Second, the high temperature speeds up all the reactions, so all the reactions are Dramatically reducing curing time (for concrete), allowing for much faster construction.”

The researchers conducted an experiment to see if lime rind was responsible for the apparent self-healing ability of Roman concrete.

They prepared two samples of concrete. One was made according to ancient Roman methods, the other by modern standards, and both were cracked on purpose. After two weeks, the Roman-style concrete became impermeable, but the concrete block without quicklime was permeable.

The results indicate that lime scale dissolves on contact with water, flows into cracks, recrystallizes, and heals cracks caused by weathering before it multiplies. The researchers note that the self-healing ability of lime crust lasts longer than traditional concrete, and thus could pave the way for the production of a modern, more sustainable version of concrete. Using self-healing concrete can also reduce concrete’s “carbon footprint,” which accounts for up to 8% of global greenhouse gas emissions, according to the study.

Researchers have long attributed the strength of Roman concrete to volcanic ash from Pozzuoli, along the Gulf of Naples. This type of volcanic ash was transported throughout the vast Roman Empire for use in construction, and is presented as an important material for concrete in the accounts of architects and historians of the time.

Both[lime and volcanic ash]are important ingredients, Macick says, but lime has been overlooked until now.

The research has been published in the US scientific journal Science Advances.