Compositional Analyses of Concretes Drilled from Harbour Structures by ROMACONS
Compositional analyses of various components of the ancient maritime concretes and the concrete reproduction at Brindisi add to the descriptions of the drill cores in Appendix 3. These include the mineral assemblages detected in powdered specimens determined through X-ray diffraction analyses, mainly at CTG Italcementi Laboratories in Bergamo, Italy (Table A4.1); major and trace element geochemistry of the tuff caementa, pumice pozzolan clasts, and pozzolanic mortars determined through ICP-MS analyses of 3 to 5 gram powdered specimens in fused glass beads at Activation Laboratories in Ancaster, Canada (Table A4.2); and major element compositions of the pozzolanic mortars determined through X-ray Fluorescence analyses of powdered specimens at CTG Italcementi Laboratories in Bergamo, Italy (Table A4.3). Note that the volcanic tuff and pozzolanic mortar specimens are hybrid materials and have a mixed character. The tuffs are composed of “juvenile” components of pumice and crystals derived from the magma of the eruption, as well as lithic fragments, mainly lava rock particles, derived from the volcanic edifice. The ratios of immobile trace elements are, therefore, only qualitative estimates of eruptive provenance. The consistent pyroclastic fabrics of the tuff caementa of the central Italian harbour concretes – with the exception of the distinctive Tufo Lionato caementa at Portus – suggest that their clustered compositions in the diagrams of Figs 7.10–11 can be interpreted as a qualitative representation of volcanic provenance. The mortars are also mixed materials, or materies miscenda as described by Vitruvius (De architectura 2.4.1, pp. 15–16, Passage 5), and their composition is very heterogeneous both at the centimeter scale of the powdered samples and the point counts of thin sections with the petrographic microscope (Table 7.1). Numerous processes could have influenced their bulk chemical compositions, so the results of major element chemical analyses are described only as qualitative chemical trends (Figs. 7.16, 7.17). For descriptions of analytical methods, see pp. 186–87. For results of laboratory analyses describing the material and mechanical characteristics of the concretes see Chapter 7.
Table A4.1: Mineralogical compositions of components of the sea-water concretes, determined through powder X-ray diffraction analyses.
(1) Italics denote specimen with XRD, major and trace element analyses (Table A4.2)
(2) Asterisk (*) denotes specimen XRD and major element analyses (Table A4.3)
(3) Cementitious matrix is the <0.145 mm size fraction, lightly crushed and sieved from the mortar
(4) Zeolites in the mortar are unreacted constituents of the pumiceous pozzolan (Stanislao et al. 2011)
(5) Vola et al. 2011
Abbreviations of crystalline phases identified through X-ray diffraction analyses of components of ancient mortars and coarse aggregate (caementa). Crystalline phases include: Afw: Afwillite; Ank: Ankerite; Arg: Aragonite; Brc: Brucite; Bsn: Bassanite; Cal: Calcite; Cbz: Chabazite; Clc: Clinochlore; Etr: Ettringite; Fl: Fluorite; Gp: Gypsum; Hal: Halite; Hyc: Hydrocalumite; Hyt: Hydrotalcite; Mnt: Montmorillonite; Non: Nontronite; Nor: Nordstrandite; Phi: Phillipsite; Por: Portlandite; Sjg: Sjogrenite; Sm: Smectite; Str: Strätlingite; Tbm: Tobermorite; Vat: Vaterite, Wo: Wollastonite. Volcanic pozzolan (tuff pumice and lava fragments) phases include primary crystals: Alb: Albite; Anl: Analcime; An: Anorthite; Aug: Augite; Bio: Biotite; Di: Diopside; Hem: Hematite; Lct: Leucite; San: Sanidine; and authigenic alteration components: Cal: Calcite; Cbz: Chabazite; Hal: Halloysite; Ill: Illite; Kao: Kaolinite; Phi: Phillipsite. Sedimentary sands and coarse aggregates include: Cal: Calcite; Dol: Dolomite; Mg-Cal: Magnesium Calcite; Mic: Microcline; Ms, Mus: Muscovite; Ort: Orthoclase; Prg: Pargasite; Qtz: Quartz; San: Sanidine.
