Cement Microstructures and Durability in Ancient Roman Seawater Concretes
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| Year of publication | 2012 |
| Type | Chapter of a book |
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| Description | Roman hydraulic maritime concretes of the central Italian coast have pumiceous volcanic ash, or pulvis Puteolanus, from the Bay of Naples as mortar pozzolan. Petrographic and mineralogical analyses of cement microstructures in relict lime, tuff, and pumice clasts suggest that pozzolanic reaction at high pH produced gel-like CASH cements. Orthorhombic 11A-tobermorite, with unit cell dimensions a=5.591(1)A, b=3.695(1)A, c=22.86(1)A, developed in the residual cores of portlandite clasts and in some pumiceous clasts. Ettringite and calcium-chloroaluminate formed in peripheral microstructures. Phillipsite and chabazite cements may reflect later dissolution of alkali-rich volcanic glass at pH 9–10. The cement systems have remained relatively stable for 2000 years, during partial to full immersion in seawater. Vitruvius’ De architectura and other ancient texts describe the raw materials of the concretes, preparation of lime, and construction of submerged wooden forms. Information concerning the materials, formulations, and installations of the concretes was apparently spread by movement of central Italian engineers around the Mediterranean but also, perhaps, by the circulation of sub-literary engineering manuals. Further analytical investigations will determine the diverse chemical processes that produced the cement microstructures, and why the harbour constructions have endured for two millennia. |
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