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    Unlocking the secrets of Al-tobermorite in Roman seawater concrete

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    Type
    Article
    Authors
    Jackson, Marie D.
    Chae, Sejungrosie
    Mulcahy, Sean R.
    Meral, Cagla
    Taylor, Rae
    Li, Penghui
    Emwas, Abdul-Hamid M.
    Moon, Juhyuk
    Yoon, Seyoon cc
    Vola, Gabriele
    Wenk, Hans Rudolf
    Monteiro, Paulo José Meleragno
    KAUST Department
    Imaging and Characterization Core Lab
    Advanced Nanofabrication, Imaging and Characterization Core Lab
    KAUST Grant Number
    KUS-11-004021
    Date
    2013-10-01
    Online Publication Date
    2013-10-01
    Print Publication Date
    2013-10-01
    Permanent link to this record
    http://hdl.handle.net/10754/563028
    
    Metadata
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    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 Q 2(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 sea-water 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.
    Sponsors
    This research was supported by Award No. KUS-11-004021, from King Abdullah University of Science and Technology (KAUST) and the Loeb Classical Library Foundation at Harvard University. Data were acquired at beamlines 5.3.2.1, 5.3.2.2, and 12.2.2 at the Advanced Light Source at the Lawrence Berkeley Laboratories supported by the Director of the Office of Science, Department of Energy, under Contract No. DE-AC02-05CH11231, and the Advanced Nanofabrication Imaging and Characterization Laboratories at King Abdullah University of Science and Technology. We thank the ROMACONS drilling program: J.P. Oleson, C. Brandon, R. Hohlfelder, and CTG Italcementi researchers and staff, especially B. Zanga, in Bergamo, Italy; A.D. Kilcoyne and T. Tyliszczak at the 5.3.2.1, 5.3.2.2 beamlines; and S. Clark at the 12.2.2 beamline. T. Teague, D. Hernandez, B. Black, C. Hagen, and C. Kosso provided research support. We thank M. Sintubin, G. Sposito, R-A. Itty, P. Brune, and J. Kirz for critical discussions, and the anonymous reviewers whose comments improved the manuscript. H.-R. Wenk acknowledges support by NSF (EAR-0836402). The Berkeley Research Impact Initiative provided funds for Open Acess.
    Publisher
    Mineralogical Society of America
    Journal
    American Mineralogist
    DOI
    10.2138/am.2013.4484
    ae974a485f413a2113503eed53cd6c53
    10.2138/am.2013.4484
    Scopus Count
    Collections
    Articles; Imaging and Characterization Core Lab

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