Evaluation of the hydraulicity of ancient Roman mortars: the aqueducts of ancient Rome

The aqueducts built by ancient Romans are not only majestic archaeological ruins, but the tangible expression of the technological level reached in the hydraulic mortar production, as some of them are still in function. Beyond the characterization of the materials constituting the mortars, using techniques already consolidated in the field, such as optical microscopy (OM), X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM-EDS), a relevant aspect is the evaluation of the hydraulicity of the mortar. Thermogravimetric analysis (TGA) has been applied at this purpose, as with this technique it is possible to evaluate the loss of carbonate phases (over 600 °C) and the loss of water in hydraulic compounds (200-600 °C) (Bakolas et al., 1998; Biscontin et al., 2002; Rizzo et al., 2008). The analysis has been applied on the sole binder fraction: each of the 76 mortar samples, collected from the inner duct of ancient Roman aqueducts in the surroundings of Rome, have been mechanically sieved, and only the fraction smaller than 63 µm (Maravelaki-Kalaitzaki et al., 2003), which is reported to be the most representative of the binder, has been investigated. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) has been performed on each sample, before and after TGA. TGA analyses on powders have been carried out at ISTerre (Grenoble, France), with a TGA-DSC3+ Mettler Toledo instrument, burning the sample from 25 to 1000 °C, under N2, with a heating rate of 10 °C/min. The calculation of CO2/H2O ratio firstly allowed to highlight the hydraulic nature of all the samples analyzed. Moreover, it permitted to define which samples contains more hydraulic phases than others, and correlate the TGA data with the characterization performed with OM, XRPD and SEM-EDS. The samples showing higher hydraulicity are also the ones that present an amorphous binder at OM, do not contain calcite at XRPD and have a binder rich in Si and Al at SEM-EDS. Moreover, these samples are also the ones coming from the two still functioning Roman aqueducts: Aqua Virgo and Aqua Traiana. REFERENCES Bakolas A., Biscontin G., Moropoulou A. & Zendri, E. (1998) - Characterization of structural byzantine mortars by thermogravimetric analysis. Thermochim. Acta, 321(1-2), 151-160, https://doi.org/10.1016/S0040-6031(98)00454-7. Biscontin G., Birelli M. P. & Zendri E. (2002) - Characterization of binders employed in the manufacture of Venetian historical mortars. J. of Cult. Herit., 3(1), 31-37, https://doi.org/10.1016/S1296-2074(02)01156-1. Maravelaki-Kalaitzaki P., Bakolas A. & Moropoulou A. (2003) - Physico-chemical study of Cretan ancient mortars. Cem. Concr. Res., 33(5), 651-661, https://doi.org/10.1016/S0008-8846(02)01030-X. Rizzo G., Ercoli L., Megna B. & Parlapiano M. (2008) - Characterization of mortars from ancient and traditional water supply systems in Sicily. J. Therm. Anal. Calorim., 92, 323-330, https://doi.org/10.1007/s10973-007-8758-4.