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Article
Unlocking the Secrets of Al-tobermorite in Roman Seawater Concrete
Geology Faculty Publications
  • Marie D. Jackson
  • Sejung R. Chae
  • Sean R Mulcahy, Western Washington University
  • Cagla Meral
  • Rae Taylor
  • Penghui Li
  • Abdul-Hamid Emwas
  • Juhyuk Moon
  • Seyoon Yoon
  • Gabriele Vola
  • Hans-Rudolf Wenk
  • Paulo J.M. Monteiro
Document Type
Article
Publication Date
1-1-2013
Keywords
  • Al-tobermorite,
  • ancient Roman concrete,
  • bonding environments,
  • volcanic pozzolan,
  • thermal mode
Disciplines
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 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.

Subjects - Topical (LCSH)
Pozzuolanas--Italy--Pozzuoli Gulf; Volcanic ash, tuff, etc.-- Italy--Pozzuoli Gulf; Lime-- Italy--Pozzuoli Gulf
Geographic Coverage
Pozzuoli Gulf (Italy)
Genre/Form
articles
Type
Text
Language
English
Format
application/pdf
Citation Information
Marie D. Jackson, Sejung R. Chae, Sean R Mulcahy, Cagla Meral, et al.. "Unlocking the Secrets of Al-tobermorite in Roman Seawater Concrete" Vol. American Mineralogist Iss. 98 (2013) p. 1669 - 1687
Available at: http://works.bepress.com/sean-mulcahy/13/