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Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete

Marie D. Jackson, Sean R. Mulcahy, Chen Heng, Li Yao, Li Qinfei, Piergiulio Cappelletti and Hans-Rudolf Wenk
Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete
American Mineralogist (July 2017) 102 (7): 1435-1450

Abstract

Pozzolanic reaction of volcanic ash with hydrated lime is thought to dominate the cementing fabric and durability of 2000-year-old Roman harbor concrete. Pliny the Elder, however, in first century CE emphasized rock-like cementitious processes involving volcanic ash (pulvis) "that as soon as it comes into contact with the waves of the sea and is submerged becomes a single stone mass (fierem unum lapidem), impregnable to the waves and every day stronger" (Naturalis Historia 35.166). Pozzolanic crystallization of Al-tobermorite, a rare, hydrothermal, calcium-silicate-hydrate mineral with cation exchange capabilities, has been previously recognized in relict lime clasts of the concrete. Synchrotron-based X-ray microdiffraction maps of cementitious microstructures in Baianus Sinus and Portus Neronis submarine breakwaters and a Portus Cosanus subaerial pier now reveal that Al-tobermorite also occurs in the leached perimeters of feldspar fragments, zeolitized pumice vesicles, and in situ phillipsite fabrics in relict pores. Production of alkaline pore fluids through dissolution-precipitation, cation-exchange and/or carbonation reactions with Campi Flegrei ash components, similar to processes in altered trachytic and basaltic tuffs, created multiple pathways to post-pozzolanic phillipsite and Al-tobermorite crystallization at ambient seawater and surface temperatures. Long-term chemical resilience of the concrete evidently relied on water-rock interactions, as Pliny the Elder inferred. Raman spectroscopic analyses of Baianus Sinus Al-tobermorite in diverse microstructural environments indicate a cross-linked structure with Al (super 3+) substitution for Si (super 4+) in Q (super 3) tetrahedral sites, and suggest coupled [Al (super 3+) +Na (super +) ] substitution and potential for cation exchange. The mineral fabrics provide a geoarchaeological prototype for developing cementitious processes through low-temperature rock-fluid interactions, subsequent to an initial phase of reaction with lime that defines the activity of natural pozzolans. These processes have relevance to carbonation reactions in storage reservoirs for CO (sub 2) in pyroclastic rocks, production of alkali-activated mineral cements in maritime concretes, and regenerative cementitious resilience in waste encapsulations using natural volcanic pozzolans.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 102
Serial Issue: 7
Title: Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete
Affiliation: University of Utah, Department of Geology and Geophysics, Salt Lake City, UT, United States
Pages: 1435-1450
Published: 201707
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 84
Accession Number: 2017-064768
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendices
Illustration Description: illus. incl. 3 tables, sketch map
N36°30'00" - N47°30'00", E06°30'00" - E19°00'00"
Secondary Affiliation: Western Washington University, USA, United StatesSoutheast University, CHN, ChinaXi'an Jiaotong University, CHN, ChinaHarbin Institute of Technology, CHN, ChinaUniversita degli Studi di Napoli Federico II, ITA, ItalyUniversity of California at Berkeley, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201734
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