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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu


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1945-3027
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Volume 98, Issue 10

Issues

Unlocking the secrets of Al-tobermorite in Roman seawater concrete

Marie D. Jackson
  • Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, U.S.A.
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/ Sejung R. Chae
  • Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, U.S.A.
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/ Sean R. Mulcahy
  • Department of Earth and Planetary Science, University of California, Berkeley, California 94720, U.S.A.
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/ Cagla Meral
  • Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, U.S.A.
  • Middle East Technical University, 06800, Ankara, Turkey
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/ Rae Taylor
  • Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, U.S.A.
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/ Penghui Li
  • State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing, 100084, China
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/ Abdul-Hamid Emwas
  • King Abdullah University of Science and Technology, Thuwal, 23955-6900, Kingdom of Saudi Arabia
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/ Juhyuk Moon
  • Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, U.S.A.
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/ Seyoon Yoon
  • Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, U.S.A.
  • School of Engineering, King’s College, The University of Aberdeen, Aberdeen AB24 3UE, U.K.
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/ Gabriele Vola / Hans-Rudolf Wenk
  • Department of Earth and Planetary Science, University of California, Berkeley, California 94720, U.S.A.
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/ Paulo J.M. Monteiro
  • Corresponding author
  • Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, U.S.A.
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Published Online: 2015-03-07 | DOI: https://doi.org/10.2138/am.2013.4484

Abstract

Ancient Roman syntheses of Al-tobermorite in a 2000-year-old concrete block submerged in the Bay of Pozzuoli (Baianus Sinus), near Naples, have unique aluminum-rich and silica-poor compositions relative to hydrothermal geological occurrences. In relict lime clasts, the crystals have calcium contents that are similar to ideal tobermorite, 33 to 35 wt%, but the low-silica contents, 39 to 40 wt%, reflect Al3+ substitution for Si4+ in Q2(1Al), Q3(1Al), and Q3(2 Al) tetrahedral chain and branching sites. The Al-tobermorite has a double silicate chain structure with long chain lengths in the b [020] crystallographic direction, and wide interlayer spacing, 11.49 Å. Na+ and K+ partially balance Al3+ substitution for Si4+. Poorly crystalline calcium-aluminum-silicate-hydrate (C-A-S-H) cementitious binder in the dissolved perimeter of relict lime clasts has Ca/(Si+Al) = 0.79, nearly identical to the Al-tobermorite, but nanoscale heterogeneities with aluminum in both tetrahedral and octahedral coordination. The concrete is about 45 vol% glassy zeolitic tuff and 55 vol% hydrated lime-volcanic ash mortar; lime formed <10 wt% of the mix. Trace element studies confirm that the pyroclastic rock comes from Flegrean Fields volcanic district, as described in ancient Roman texts. An adiabatic thermal model of the 10 m2 by 5.7 m thick Baianus Sinus breakwater from heat evolved through hydration of lime and formation of C-A-S-H suggests maximum temperatures of 85 to 97 °C. Cooling to seawater temperatures occurred in two years. These elevated temperatures and the mineralizing effects of seawater and alkali- and alumina-rich volcanic ash appear to be critical to Al-tobermorite crystallization. The long-term stability of the Al-tobermorite provides a valuable context to improve future syntheses in innovative concretes with advanced properties using volcanic pozzolans.

Keywords : Al-tobermorite; ancient Roman concrete; bonding environments; volcanic pozzolan; thermal model

About the article

Received: 2013-01-28

Accepted: 2013-05-07

Published Online: 2015-03-07

Published in Print: 2013-10-01


Citation Information: American Mineralogist, Volume 98, Issue 10, Pages 1669–1687, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am.2013.4484.

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© 2015 by Walter de Gruyter Berlin/Boston.

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