Jackson, Marie

The Grande Aula, or Great Hall, of the Markets of Trajan is an intact example of the sophisticated, domed, concrete architecture of imperial Rome, which records the expertise of Roman builders in formulating extraordinarily durable pozzolanic concretes between about AD 96 and 115. Petrographic, chemical, X-ray diffraction analyses and SEM images demonstrate that the pozzolanic mortars of the conglomeratic wall concretes contain strätlingite, a complex calcium aluminate cement hydrate (C2 ASH8) that gives modern cements high durability and compressive strength. It has not been previously recognized in ancient pozzolanic mortars. New methods of assessing bulk specific gravity of the porous concretes suggest unit weights of 1495 kg/m³ for the conglomeratic wall cores and 1200-1300 kg/m³ for the pumice-bearing vaulted ceiling mortar.Innovative point load tensile strength testing methods provide a means of evaluating the strengths of small samples of ancient, conglomeratic cementitious materials. Tests of coarse aggregate clasts, pozzolanic mortar, and the adhesive interfacial surfaces of coarse aggregate clasts (caementa) in contact with the mortar, suggest tensile strengths (ft) of 2.7 MPa for brick clasts, 1.2 MPa for Tufo Lionato tuff clasts, and 0.9 MPa for Tufo Giallo della Via Tiberina tuff clasts based on a tentative, approximate correlation with splitting (Brazilian) tests on these materials. The pozzolanic mortar and interfacial zones appear to have lower ft, in the range of 0.8 MPa to 0.5 MPa. The relatively low tensile strengths of the mortar and its somewhat tenuous adhesion to coarse aggregate clasts suggests that the caementa may have had a role in arresting the propagation of tensile microcracks that formed in the mortar, thereby increasing the composite tensile strength of the concrete. Roman builders evidently selected the complex aggregate mixes to optimize the performance and durability of the wall and vault masonry.

The rocks of Alban Hills and Monti Sabatini volcanoes (Central Italy) and their associated epiclastic deposits have been extensively used as building material in ancient Rome from about VIIIth century BCE to IVth century CE. However, the identification of the source areas of these rocks is difficult due to the lack of an integrated stratigraphic and geochemical analysis of the relationships between the two volcanic districts, and to the alteration affecting the primary products as consequence of weathering and pedogenetic processes. Here, a comprehensive, upgraded stratigraphic and geochronological review of the two volcanic districts, corroborated by new geochronological data for several eruptive units and altered deposits is presented, coupled to a complete geochemical background, achieved by means of newly determined major and trace element analyses for all the main eruptive units. A study of the alteration processes of the primary products is also presented, and the age of the main weathering and pedogenetic phases, associated to Quaternary climatic changes, are also investigated. The results are integrated with those from literature in order to construct discriminant diagrams based on selected trace elements, and allow us to characterize the primary and altered volcanic deposits in the Rome area, distinguish products of different volcanic districts, discuss the effects of different weathering processes on the mobility of some elements, and provide a reference frame for the provenance of the volcanic materials employed in ancient Roman masonry. The interdisciplinary data set and results presented here provide groundwork for volcanological, climate, pedological and archaeological provenance studies.

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 highquality, 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.

New archaeological excavations begun in 1998 have exposed the complexity of construction design and planning of the Basilica Ulpia and Forum of Trajan, raising new research questions and providing a unique opportunity to reexamine sectors of these structures that were the object of older excavations dating to 1812 and 1924-1933. In this article, we integrate archaeological, geological, and mechanical perspectives to reconsider diverse aspects of Roman building technology and the construction of the Forum. In particular, we investigate forms and structural stability of the integrated structural elements that constitute the upper stories of the Basilica Ulpia. Furthermore, we document the compositions of brick faced, opus latericium walls and the wall core, or nucleus, of these structures, as well as those of concrete vaults and staircases, focusing on the petrographic and material characteristics of their coarse aggregates (caementa) and the fine aggregates (harenae fossiciae) of their pozzolanic mortars. With this interdisciplinary approach, we evaluate the technical expertise of Roman builders in designing the complex concrete elements in the architectures of the Basilica Ulpia and Forum of Trajan

The hydrated lime-volcanic ash mortars of imperial age concrete construction in Rome owe their extraordinary durability to a specific alteration facies of scoriaceous ash from the Pozzolane Rosse ignimbrite, erupted at 456±3 ka from Alban Hills volcano. Stratigraphic, petrographic, and chemical investigations demonstrate that during the warm, humid period preceding marine isotope stage 11, hydrolytic pedogenesis produced an argillic horizon in Pozzolane Rosse, with thick illuvial clay that had little reactivity with hydrated lime, as shown by mortars from the Forum of Julius Caesar (46 to 44 BC). In the underlying soil horizon, however, translocated halloysite overlies opal and poorly crystalline clay surface coatings. Imperial age mortars, as from the Forum and Markets of Trajan (AD 96 to 115), show strong reactivity of these components, altered scoria groundmass, and zeolites with hydrated lime. Romans deliberately selected this alkali-rich ash for optimal performance of pozzolanic concretes.

Inter-laboratory and absolute calibrations of rock magnetic parameters are fundamental for grounding a rock magnetic database and for semi-quantitative estimates about the magnetic mineral assemblage of a natural sample. Even a dimensionless ratio, such as anhysteretic susceptibility normalized by magnetic susceptibility (Ka/K) may be biased by improper calibration of one or both of the two instruments used to measure Ka and K. In addition, the intensity of the anhysteretic remanent magnetization (ARM) of a given sample depends on the experimental process by which the remanence is imparted. We report an inter-laboratory calibration of these two key parameters, using two sets of artificial reference samples: a paramagnetic rare earth salt, Gd2O3 and a commercial "pozzolanico" cement containing oxidized magnetite with grain size of less than 0.1 m according to hysteresis properties. Using Gd2O3 the 10 Kappabridges magnetic susceptibility meters (AGICO KLY-2 or KLY-3 models) tested prove to be cross-calibrated to within 1%. On the other hand, Kappabridges provide a low-field susceptibility value that is ca. 6% lower than the tabulated value for Gd2O3, while average high-field susceptibility values measured on a range of instruments are indistinguishable from the tabulated value. Therefore, we suggest that Kappabridge values should be multiplied by 1.06 to achieve absolute calibration. Bartington Instruments magnetic susceptibility meters with MS2B sensors produce values that are 2–13% lower than Kappabridge values, with a strong dependence on sample centering within the sensor. The Ka/K ratio of ca. 11, originally obtained on discrete cement samples with a 2G Enterprises superconducting rock magnetometer and a KLY-2, is consistent with reference parameters for magnetites of grain size <0.1 m. On the other hand, Ka values from a 2G Enterprises magnetometer and K values from a Bartington Instruments MS2C loop sensor for u-channel and discrete cement samples, will produce average Ka/K values that are unrealistically high if not properly corrected for the nominal volume detected by the sensors for these instruments. Inter-laboratory measurements of K and Ka for standard paleomagnetic plastic cubes filled with cement indicate remarkable differences in the intensity of the newly produced ARMs (with a standard deviation of ca. 21%), that are significantly larger than the differences observed from the calibration of the different magnetometers employed in each laboratory. Differences in the alternating field decay rate are likely the major source of these variations, but cannot account for all the observed variability. With such large variations in experimental conditions, classical interpretation of a "King plot" of Ka versus K would imply significant differences in the determination of grain size of magnetite particles on the same material.