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Rock physics of fibrous rocks akin to Roman concrete explains uplifts at Campi Flegrei Caldera

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Science  07 Aug 2015:
Vol. 349, Issue 6248, pp. 617-621
DOI: 10.1126/science.aab1292

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Cementing Roman concrete to a caldera

Ancient concrete would seem to have little to do with volcano geology. However, Vanorio and Kanitpanyacharoen found similarities between the caprock of the Campi Flegrei caldera near Naples, Italy, and the Roman-era concrete for which the region was known. Both materials require a similar set of chemical reactions to give it the high strength caused by microstructures of intertwining fibrous minerals. The high strength of the natural rock explains the ability of the caldera to withstand periods of high-rate uplift without eruption. The Romans living in the caldera, where the town of Pozzuoli is today, may have been trying to mimic nature to produce this iconic material.

Science, this issue p. 617

Abstract

Uplifts in the Campi Flegrei caldera reach values unsurpassed anywhere in the world (~2 meters). Despite the marked deformation, the release of strain appears delayed. The rock physics analysis of well cores highlights the presence of two horizons, above and below the seismogenic area, underlying a coupled process. The basement is a calc-silicate rock housing hydrothermal decarbonation reactions, which provide lime-rich fluids. The caprock above the seismogenic area has a pozzolanic composition and a fibril-rich matrix that results from lime-pozzolanic reactions. These findings provide evidence for a natural process reflecting that characterizing the cementitious pastes in modern and Roman concrete. The formation of fibrous minerals by intertwining filaments confers shear and tensile strength to the caprock, contributing to its ductility and increased resistance to fracture.

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