A COMPARISON OF THE CHEMICAL AND ENGINEERING CHARACTERISTICS OF ANCIENT ROMAN HYDRAULIC CONCRETE WITH A MODERN REPRODUCTION OF VITRUVIAN HYDRAULIC CONCRETE*

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.     

PROVENANCING OF LIGHTWEIGHT VOLCANIC STONES USED IN ANCIENT ROMAN CONCRETE VAULTING: EVIDENCE FROM ROME

This paper presents the geochemical analysis of lightweight scoria and pumice used in concrete vaults from ancient Rome. The geochemical signatures of dark scoria indicates a provenance of the 36–18 ka lavas of Vesuvius, as opposed to the more recent events on which Pompeii was built, as previously thought. The light‐coloured pumices analysed, which were originally thought to belong to the Sabatini volcanic system (north of Rome), corresponded instead to products from Campi Flegrei. These results provoke re‐evaluation of the trade and acquisition of these specialized materials destined for imperial projects in the capital city.     

MORTAR STUDIES TOWARDS THE REPLICATION OF ROMAN CONCRETE

The use of strong and durable materials is one essential ingredient leading to the survival of many monumental Roman concrete structures. Replicated concrete mortars with different lime to pozzolan ratios, encompassing the range likely to have been used by the Romans, have been studied here to determine their relative compressive strengths as a function of time. This has been supplemented by the use of the scanning electron microscope to delve into the structure and composition of the binders formed within the strongest and weakest mortars, leading to a deeper understanding of the reasons for the differences in compressive strength.     

Interpretation of the Thermogravimetric Curves of Ancient Pozzolanic Concretes

Pozzolanic concretes submitted to thermogravimetric (TG) analysis show a continuous weight loss starting from about 400 °C. In order to reconcile these observations with those from other analytical methods, it is necessary to attribute this weight loss to CO₂ removal. It has been proposed, in the literature, that silicates and CaCO₃ react at lower temperatures, producing calcium silicates and CO₂. In this paper, the FTIR spectra collected on samples submitted to TG analysis, stopped at conveniently selected temperatures, provide direct evidence that the continuous weight loss recorded with thermogravimetric analysis of the pozzolanic concrete in the temperature range 400–900 °C is to be attributed to the reaction between the silicates and calcite, with the formation of CO₂ and of a silicate that is richer in CaO. Therefore it is justifiable that the whole weight loss, in the temperature range 400–900 °C, should be taken into account in the calculation of the CaCO₃ content of the concrete. Moreover, the described procedure—of recovering small samples (2 mg) from the sample‐holder of the TG apparatus at various steps of the heating rate and comparing the FTIR spectra—can help in identifying the pozzolanic nature of a concrete that, in general, is not easily recognizable from the trend of the thermoanalytical curve.     

BUILDING MATERIALS OF THE THEATRE OF MARCELLUS,ROME*

The building materials of the Theatre of Marcellus, 44–11 bce , reflect Roman builders' careful selections of tuff and travertine for dimension stone and volcanic aggregates for pozzolanic concretes. The vitric–lithic–crystal Tufo Lionato tuff dimension stone contains a high proportion of lava lithic fragments, which increase its compressive strength and decrease water sorption, enhancing durability. Sophisticated installations of travertine dimension stone reinforce the tuff masonry, which is integrated with durable concrete walls and barrel vaults. The pozzolanic mortars of the concretes contain harenae fossiciae mainly from the intermediate alteration facies of the mid‐Pleistocene, scoriaceous Pozzolane Rosse pyroclastic flow. They have pervasive interpenetrating pozzolanic cements, including strätlingite, similar to high‐quality, imperial era mortars. Concrete walls are faced with refined Tufo Lionato opus reticulatum and tufelli, and opus testaceum of fired, greyish‐yellow brick. The exploratory concrete masonry, which includes some of the earliest examples of brick facings and strätlingite cements in Rome, and the integration of these materials in complex architectural elements and internal spaces, reflect the highly skilled workmanship, rigorous work‐site management and technical supervision of Roman builders trained in republican era methods and materials.     

PROVENANCING OF LIGHTWEIGHT VOLCANIC STONES USED IN ANCIENT ROMAN CONCRETE VAULTING: EVIDENCE FROM TURKEY AND TUNISIA

The mastery of the use of lightweight rocks in concrete as a means of controlling the thrusts of large‐scale vaults was among the most important contributions of the Roman builders to the development of vaulted architecture. The string of volcanoes along the Tyrrhenian coast of Italy produced a variety of lightweight rocks, which allowed the builders in Rome to develop highly sophisticated ways of manipulating form and mass to create stable structures. The use of lighter rocks in vaults and heavier in foundations occurs from the mid‐first century bc in Rome, but the systematic use of imported lightweight rocks only began in the early second century ad under Trajan ( Lancaster 2005 , 59–64). Soon thereafter, the technique of using lightweight stones to build large vaults spread throughout the empire, usually to areas that had a local source of lightweight volcanic material. However, there was also a seaborne trade in lightweight rocks to areas that did not have local sources of such material. The intention of our analysis is to determine as precisely as possible the provenance of the lightweight stones used in vaulting of two areas of the Mediterranean, modern Turkey (ancient Cilicia) and Tunisia (ancient Africa Proconsularis), and thus to provide a better understanding of the nature of this trade.