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Wednesday, 29 July 2015 08:26cat

Campi Flegrei Supervolcano and the Roman Concrete

Written by  TheStructuralEngineer.info
Campi Flegrei Supervolcano and the Roman Concrete Gabriele Forzano

'Geowarn' was a European research program which was designed to explore the most dangerous areas in Europe.

The Supervolcano of Kos, where the largest volcanic eruption in East Mesogeio- 161,000 years ago took place and the volcanic region of Campania -Italy, where there is the Supervolcano CampiFlegrei and Vesuvius; a densely populated area with 3.5 million people. A new study shows that the Supervolcano Campi Flegrei produces concrete!

The concrete produced in Campi Flegrei volcano is similar to Roman concrete, a legendary compound that was invented by the Romans (to be more specific by the ancient Greeks) and was used for the construction of the Pantheon, Colossal, and ancient ports across Mediterranean.

"This implies the existence of a natural process in the subsurface of Campi Flegrei that is similar to the one that is used to produce concrete," said Tiziana Vanorio, an experimental geophysicist at the Stanford School of Earth, Energy & Environmental Sciences.

The Campi Flegrei volcano is located in the center of a great depression, or caldera, consisting of craters formed by ancient eruptions, the most recent of which occurred about 500 years ago. Within this caldera there is the colorful port city called Pozzuoli, which was founded in 600 BC by the Greeks.

In 1982, the ground beneath Pozzuoli began to rise at an alarming rate. Within a period of two years, the elevation exceeded 2m. "The rising sea bottom rendered the Bay of Pozzuoli too shallow for large craft," Vanorio said.

The swelling of the soil was accompanied by earthquakes. When a 4M earthquake hit Pozzuoli, the authorities evacuated the city.

Vanorio who was a teenager at that time, was among the 40,000 residents who were forced to leave Pozzuoli and settled in towns between Naples and Rome. That was the reason for her to become geophysicist. Now as an assistant professor at Stanford University, Vanorio decided to apply her knowledge on how the rocks deep in the Earth can respond to mechanical and chemical changes, in order to investigate how the ground beneath Pozzuoli was able to endure so much deformation and elevation before cracks of earthquakes.

To understand why the surface of the caldera was able to host incredible intensity without sudden cracks, Vanorio and colleagues examined the area. In 1980, a deep drilling program was carried out in the active geothermal system of Campi Flegrei in a depth of about two miles. When scientists analyzed the rock samples, they discovered that the overlying rocks-a hard rock layer at Campi Flegrei had pozzolan and volcanic ash from the area.

The scientists also observed that the overlying rocks containing tobermorite and ettringite, which are fibrous minerals that exist in manmade concrete. These substances made overburden rocks of Campi Flegrei to be more ductile, and its presence explains why the ground beneath Pozzuoli was able to withstand considerable bending / deformation before breaking. But what made tobermorite and ettringite to be formed?

The samples showed that the caldera was consisting of carbonate-like limestone, and scattered into the carbonate rocks there was a mineral called actinolite.
"The actinolite was the key to understanding all of the other chemical reactions that had to take place to form the natural cement at Campi Flegrei," the researchers said.

"This is the same chemical reaction that the ancient Romans unwittingly exploited to create their famous concrete, but in Campi Flegrei it happens naturally," Vanorio said.
In fact, Vanorio believes that the Romans inspired from the observation of interactions between volcanic ash in Pozzuoli and seawater in the area. According to the Roman philosopher Seneca 'dust at Puteoli becomes stone when it touches the water.'

''The Romans keen observers of the natural world and fine empiricists '' said Vanorio.

Pozzuoli was the main commercial and military port of the Roman Empire, and ships used the pozzolan as ballast during the marketing of grain from the eastern Mediterranean. Consequently, the volcanic ash from Campi Flegrei, and the use of the Roman concrete spread throughout the ancient world. Archaeologists have recently discovered that piers in Alexandria, Caesarea, and Cyprus are all made from Roman concrete.

 

Source: stanford.eduIBT

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