The Secret of Ancient Roman Architecture

The Romans began to make concrete more than 2000 years ago, but it is not exactly the same as today's concrete. They have a different formula, which leads to a substance that is not as strong as modern products. However, buildings such as the Pantheon and the Colosseum have existed for centuries and are usually rarely maintained. Geologists, archaeologists and engineers are studying the characteristics of ancient Roman concrete to solve the mystery of its life. It is much more fragile than modern concrete. Lei Natuo Perrucci, a mechanical engineer at the University of Rochester in New York, said: "Its strength is about 10 times of the original." . "This material is considered to have a significant resistance that varies with time."

This resistance or durability to the natural environment may be due to one of the key components of concrete: volcanic ash. Modern concrete is a mixture of lime-based cement, water, sand and so-called fine gravel. The formula of Roman concrete also started from limestone: the builders burned it into quicklime and then added water to make it into a paste. According to the works of Vitruwe, an architect and engineer in the first century BC, they then mixed volcanic ash (usually three parts volcanic ash and one part lime). Volcanic ash reacts with lime slurry to form durable mortar, which is combined with bricks or volcanic rocks of the first size (called tuff) and then filled in place to form a structure similar to a wall or vault. At the beginning of the 2nd century BC,

. The Romans have used this kind of concrete in large-scale construction projects, which shows that their experiments on this building material began even earlier. Other ancient societies, such as the Greeks, may also use lime mortar (in ancient China, glutinous rice was added to enhance strength). However, Perrucci said that it may be an invention of Rome to combine mortar with aggregates such as bricks to make concrete.

In the earliest concrete, the Romans mined ashes from various ancient volcanic sediments. But in 27 BC, Augustus became the first Roman emperor, and construction workers became picky. At that time, Augustus launched an extensive plan to repair old monuments and build new ones throughout the city. Construction workers specialize in using volcanic ash. Volcanic ash comes from volcanic ash deposition, and volcanic ash flow erupted for 456 years. 1000 years ago, the Pantheon was completed in 128 years, located on the hill of Mount alban 12 mile southeast of Rome. The dome of this temple is still the largest unreinforced concrete dome in the world. (Guido Bogman/Bundesregierung Pool via Getty Images) The Colosseum in Rome was built in 80 AD, with a capacity of 50,000 people. Gladiator competitions, animal hunting ceremonies, * * and executions were held. (Tiziana Fabi/AFP/Getty Images) Tomb of Cassilia metra, daughter of Roman consul. This Daguerre photo of 184 1 is one of the earliest known Italian photos. (SSPL/ Getty Photo Agency) Tempio di Venere Roma is a temple dedicated to two goddesses, which was inaugurated by Emperor Hadrian in 135. Mary, a geologist and research engineer at the University of California, Berkeley? Mary Jackson said:

"Emperor Augustus is the driving force of systematization and standardization of mortar and volcanic ash mixture." She added that Roman builders might prefer this ash deposit because the concrete made of it is durable. "This is the secret of concrete. Concrete is a very good combination, coherent and solid material."

Jackson and her colleagues have been studying the chemical composition of concrete made of volcanic ash roses. The unique mineral combination of volcanic ash seems to help concrete resist chemical corrosion and destruction.

The Romans liked another special kind of volcanic ash, when the concrete port structure was submerged in the salt water of the Mediterranean. Shell-and-core powder is mined from sediments near the Gulf of Naples. "The Romans transported thousands of tons of volcanic rocks" and built ports around the Mediterranean, from the Italian coast to Israel, from Alexandria in Egypt to Pompeii in Turkey, "Jackson said.

Modern concrete was badly damaged by seawater. But in Roman concrete, the shell-core powder "actually played a role in alleviating the deterioration of water infiltration," Jackson said. Although the exact mechanism is not clear, the chemical reaction between lime slurry, volcanic ash and seawater seems to form a microstructure in concrete, which captures molecules such as chloride and sulfate, which are harmful to concrete today.

Despite the success of Roman concrete, the use of this material disappeared with the disappearance of the Roman Empire. Perruccio said that few concrete structures were built in the Middle Ages, which shows that volcanic ash is not the only secret of the durability of Roman concrete. "These truly large-scale projects can only be completed through the appropriate bureaucracy and appropriate organization provided by the Roman Empire."

Eileen Weiman is an assistant editor of the Smithsonian Institution. She wrote a blog about primitive hunting.