Roman concrete, one of the world's most durable compounds, closely resembles the rock formed in the depths of a dormant supervolcano in Italy, suggesting that ancient Romans mimicked nature when they created their resilient, impermeable mortar.
Used to construct monuments such as the Pantheon and the Coliseum, Roman concrete has withstood two millennia of attacks by time and the elements, including wave and water, since it was also used to create artificial harbors throughout the Mediterranean.
Tiziana Vanorio, professor at the Geophysicist Department, Stanford's School of Earth, Energy & Environmental Sciences, discovered that a natural process reflecting that of the engineering of the Roman concrete occurs in the subsurface of Campi Flegrei (Phlegraean Fields),a large volcanic area west of Naples.
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The rock's microstructures in these sunken volcanic fields have shown an exceptional strength, able to withstand tremendous strains.
Campi Flegrei lies at the center of a large depression, or caldera, and comprises fissures and craters formed during past eruptions, the last of which occurred in 1538.
The city of Pozzuoli is nestled within the caldera and was founded in 600 B.C. by the Greeks. Known to Italians as the birthplace of movie star Sophia Loren, the city was in Roman times one of the major trading ports of the Mediterranean, called Puteoli.
Beginning in 1982, the ground beneath Pozzuoli began rising at an alarming rate. Within two years, the town was raised by six feet - an amount unprecedented anywhere in the world.
The ground swelling was accompanied by persistent seismic activity, and nearly 40,000 people were evacuated from Pozzuoli.
"Ground swelling occurs at other calderas such as Yellowstone or Long Valley in the United States, but never to this degree, and it usually requires far less uplift to trigger earthquakes at other places," Vanorio said.
"At Campi Flegrei, the micro-earthquakes were delayed by months despite really large ground deformations," she added.
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To answer the long standing question of why the subsurface of the caldera was able to accommodate the deformation without immediately releasing the stored energy through rock fracturing or cracking, Vanorio and a post-doctoral associate, Waruntorn Kanitpanyacharoen, now at Chulalongkorn University in Thailand, analyzed the rock cores from wells that were drilled in the caldera just before the Pozzuoli uplift.
The results, detailed today in Science, showed impressive similarities with the Roman concrete engineering.
"The Roman concrete was made by mixing slaked lime and pozzolana, the volcanic ash from Campi Flegrei. Similar to this technique, the natural process in Campi Flegrei forms a layer, laying between 3200 and 6500 feet, that is made up of a fibrous substance resulting from the mixture of lime and pozzolana," Vanorio told Discovery News.
The core samples showed that in the Campi Flegrei caldera, the natural lime comes from the decomposition of deep carbonate rocks due to the presence of high temperature and mineral fluids, a process called decarbonation.
"Once formed, the lime is transported by the geothermal fluids up to shallower depths where it finds the rock layer made of pozzolana ash and reacts with it," Vanorio said.
"It is this reaction that leads to the formation of fiber minerals, Tobermorite and Ettringite, that are also found in man-made concrete, including Roman concrete," she added.