An Archaeological-Geological-Engineering Approach to Understanding the Durability of Ancient Roman Seawater Concretes

Peer-Reviewed Scientific Publications

Jackson, M., G. Vola, D. Vsiansky, J. Oleson, B. Scheetz C. Brandon, R. Hohlfelder, in press, Cement microstructures and durability in ancient Roman seawater concretes, Historic Mortars, Characteristics and Tests, edited by J. Valek, C. Groot, and J. Hughes. Springer – RILEM.

Abstract 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 calcium-aluminum-silica-hydrate cements. Orthorhombic 11Å-tobermorite, with unit cell dimensions a=5.591(1)Å, b=3.695(1)Å, c=22.86(1)Å, developed in the residual cores of portlandite clasts and in certain pumiceous clasts, as well. Ettringite and calcium-chloroaluminate formed in discrete, perimetral microstructures and in the cementitious matrix. Phillipsite and chabazite cements may reflect later dissolution of alkali-rich volcanic glass at pH 9–10. The cement systems have remained 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.

Stanislao, C., Rispoli, C., Vola, G., Cappellettoi, P., Morra, V. and De’ Gennaro, M. 2011, Contribution to the knowledge of ancient Roman seawater concretes: the Phlegrean pozzolan adopted in the construction of the harbour at Soli-Pompeiopolis (Mersin, Turkey). Periodico di Mineralogia, Special Issue Devoted to Prof. Franco Enrico, 80:3 (Special Issue), 471-488. [DOI:10.2451/2011PM0031].

Abstract This study deals with the characterization of ancient seawater concretes from the Roman harbour of Soli-Pompeiopolis, 1st century B.C., at Mersin in Turkey, drilled by the ROMACONS (Roman Maritime Concrete Study) team in 2009. This research activity was performed in collaboration with the Laboratories Department of CTG Italcementi Group and the Earth Sciences Department of the University “Federico II” of Naples. Results confirmed that the Roman engineers extensively used coarse tuff aggregate, lime hydrated in seawater, and pozzolanic volcanic fine sand, the so-called pulvis puteolanus of Vitruvius’s treatise De Architectura (1st century B.C.). The typical mineralogical association of phillipsite > chabazite > analcime, in particular points out the provenance for the tuff aggregate from the Yellow Neapolitan Tuff (NYT) formation, which is connected to the Campi Flegrei volcanic activity, dated back to 15.000 years ago. As far as the fine pozzolanic sand, of which just some scoria relics have been observed, can be ascribed to the same formation, or, probably, to the pozzolan stricto sensu pyroclastic flow from the Campi Flegrei area, as well. EDS microanalyses of different phillipsite crystals showed that the content of major alkaline and alkaline-earth metals was very close to those of phillipsite crystals from NYT, with K higher than Na and Ca, as previously reported in the literature. This fact clearly attests that zeolites were not involved in cation exchange processes within the seawater, despite of their long time curing - approximately two thousand years - in the marine environment.

Vola, G., Gotti, E., Brandon, C., Oleson, J. P., and Hohlfelder, R.L., 2011, Chemical, mineralogical and petrographic characterization of Roman ancient hydraulic concretes cores from Santa Liberata, Italy, and Caesarea Palestinae, Israel. Periodico di Mineralogia, 80:2, 317-338 [DOI:10.2451/2011 PM0023].

Abstract This study reports chemical, mineralogical and petrographic characterization of ancient hydraulic concretes from the Roman piers at Santa Liberata Orbetello (Grosseto) Italy (~ 50 B.C.), and breakwaters at the harbour of Caesarea Palestinae, Israel (c. 25 B.C.), drilled by the ROMACONS (Roman Maritime Concrete Study) team in 2003-2005. Both sets of concrete contain a pozzolanic sanidine- and clinopiroxene-bearing tuff, identified as coming from the pyroclastic deposits of the Phlegrean Fields (Naples), the so-called pulvis Puteolanus of Vitruvius. However, the content of tuff changes, being predominant at Santa Liberata, whereas it is only a smaller fraction of the total aggregate at Caesarea that is mostly composed of local kurkar calcareous sandstone, with occasional ceramic fragments. The cementitious binding matrix presents amorphous gel-like, silica-rich C-A-S-H, with subordinated “sparry” calcite cement, and unusual dull white grains composed of calcite, tobermorite, and ettringite, apparently derived from reaction with hydrated lime in seawater. Saline encrustations, from the diffusion of chlorides and sulphates, and characteristic authigenic spherical zeolites with the “rosette” texture also occur within the mortar’s porosity. These new data put further constraints on the various reactions occurring in roman concretes in over two thousand years of curing in an aggressive marine environment.

Gotti, E., Oleson, J. P., Bottalico, L., Brandon, C., Cucitore, R., and Hohlfelder, R. L. (2008) A comparison of the chemical and engineering characteristics of ancient Roman hydrauli concrete with a modern reproduciton of Vitruvian hydraulic concrete, Archaeometry 50, 576-590. [DOI: 10.2451/2011PM0031]

Abstract. The authors have completed structural and compositional analysis of Roman hydraulic concrete using large cores taken from a variety of maritime structures. In 2005 an 8 m³ block of hydraulic, pozzolanic concrete was built in the sea at Brindisi (Italy), applying the materials and procedures specified by the Roman architect Vitruvius. Cores were taken at 6 months and 12 months after construction and subjected to the same analyses as the first-century bc cores from pilae associated with the Villa of the Domitii Ahenobarbi at Santa Liberata. Results show that a slight variation on the Vitruvian formula yields results closest to the Roman material, and that substantial curing requires 12 months.

Presentations, Papers and Posters at Conferences

Vola, G., Stanislao, C., Rispoli, C., Morra, V. e De’ Gennaro, M. 2011, Analisi petrografica quantitativa di malte pozzolaniche provenienti da antichi calcestruzzi marini di età romana, campionati dal Romacons team (2006-2009), in A. GIULIANI (a cura di): Rocce minerali industriali, Atti della Sessione 16 - 85° Congresso Nazionale della Società Geologica Italiana, Pisa 6-8 settembre 2010, Aracne Editrice, Roma, 29-41 [ISBN 978-88-548-3745-4].

Vola, G., Stanislao, C., Rispoli, C., Morra, V. e De’ Gennaro, M., 2010, Petrographic quantitative analysis of pozzolanic mortars from ancient Roman marine concrete cores, drilled by Romacons team (2006-2009). Rendiconti online della Società Geologica Italiana, 11:2, 563-564 (with poster).

Oleson, J., and Jackson, M., 2010, How did expertise in maritime hydraulic concrete spread through the Roman empire? In Proceedings of the Second Historic Mortars Conference (HMC 2010) and RILEM TC 203-RHM Final Workshop, 22-24 September, 2010, Prague, Czech Republic, edited by J. Válek, C. Groot, and J. Hughes, 285-292, [e-ISBN:978-2-35158-112-4].

Vola, G., Jackson, M., Oleson, J., Brandon, C., Hohlfelder, R., 2010, Mineralogical and petrographic characterisation of ancient Roman maritime concretes, In Proceedings of the Second Historic Mortars Conference (HMC 2010) and RILEM TC 203-RHM Final Workshop: 22-24 September, 2010, Prague, Czech Republic, edited by J. Válek, C. Groot, and J. Hughes, 381-388 (with poster) [e-ISBN: 978-2-35158-112-4].

Jackson, M., Vola, G., Scheetz, B., Oleson, J., Brandon, C. and Hohlfelder, R.L., 2010, Chemical durability of cement systems in pozzolanic mortars of ancient Roman seawater concretes, In Proceedings of the Second Historic Mortars Conference (HMC 2010) and RILEM TC 203-RHM Final Workshop, 22-24 September 2010, Prague, Czech Republic, 217-225 [e-ISBN: 978-2-35158-112-4].