# Investigations on an Ancient Mortar from Ulpia Traiana Sarmizegetusa Archaeological Site, Romania
## 3 Results
### ATR-FTIR Results  
FTIR analysis, given in Figure 12, was performed in two areas: the first was a white area (red curve) and the second a grey area of the matrix (blue curve). Both curves have absorbance peaks at the same position; what differs is their band intensity ratio. For example, peaks at 1418, 873, and 711 cm\({}^{-1}\), respectively, can be attributed to calcite and have a higher amplitude for white areas (red curve), confirming that these areas contain more CaCO\({}_{3}\) than the grey areas. A broad, asymmetric feature in the range of 1200-900 cm\({}^{-1}\) may indicate, with a high probability, the existence of albite feldspar, which was found in the XRD analysis (Figure 4); however, many minerals that come from granite/gneiss rocks containing Si-O (biotite, quartz) or kaolinite could be found in that area. The 520 and 441 cm\({}^{-1}\) peaks identify the presence of quartz (or Si-O-Si in other minerals) in similar concentrations in the two samples. The broad band peaking at 3391 cm\({}^{-1}\) is related to the existence of -OH groups; this may indicate the presence of adsorbed water and is directly related to the observed high porosity. This band will mask the peaks of the hydroxyl groups in biotite or kaolinite. No evidence of calcium hydroxide (CH) could be found, even in the ATR mode (CH could be identified by its sharp peak at 3640 cm\({}^{-1}\)), as its signal can be hidden if the CH concentration is low enough. Figure 12: FTIR analyses on two areas of the specimen: white (red curve), grey (blue curve). Previous literature data [19; 35] were used to identify functional groups like CO\({}_{3}\)\({}^{2-}\) and Si-O and their characteristic FTIR peaks. Differentiation between anthropogenic (pyrogenic) and geogenic CaCO\({}_{3}\) can be achieved using Fourier-transform infrared spectroscopy (FTIR) and the luminescence properties of calcium carbonate [36]. Both methods are based on different densities and distributions of atomic defects in the calcite crystal structure. In calcite, three major infrared absorption peaks are identified: \(\
u_{2}\) out-of-plane bending CO\({}_{3}\)\({}^{2-}\) (873 cm\({}^{-1}\)), \(\
u_{3}\) asymmetric stretching CO\({}_{3}\)\({}^{2-}\) (1418 cm\({}^{-1}\)), and \(\
u_{4}\) in-plane bending CO\({}_{3}\)\({}^{2-}\) (711 cm\({}^{-1}\)). It was shown that the ratio between \(\
u_{2}\) and \(\
u_{4}\) bands' intensities reflects the order of the calcite crystal structure [37]. A high ratio is indicative of disorder in the crystal, i.e., the calcite is a pyrogenic, while at low values of the ratio (around 3), the calcite has a geogenic origin [37]. The analysis of Figure 12 according to the procedure given in [37] confirmed, based on the values of the ratio of the infrared absorption peaks, \(\frac{\
u_{2}}{\
u_{4}}\cong 8\) for lumps and \(\cong 5.7\) for grey areas (binder), that the origin of the calcite in the examined specimens is pyrogenic, highlighting the absence of S1 geogenic calcite. A higher value ratio for lumps suggests this material to be radiocarbon dated. To confirm the existence of biotite, FTIR microscopy and maps were recorded. The red cross is placed, in Figure 13a, on the dark particle of about 0.5 mm size. FTIR maps corresponding to Si-O-Si groups and Al-O-Si groups, corroborated by the color, indicate that the particle is most likely made of biotite. Figure 13b shows an FTIR map plotted at 1005 cm\({}^{-1}\), corresponding to Si-O-Si groups, which could indicate biotite, having the highest absorbance in the area of the particle. Figure 13c gives the FTIR map recorded at 728 cm\({}^{-1}\), corresponding to Al-O-Si groups, which could indicate biotite, showing the highest absorbance in the area of the particle. Note that the larger, white particle to its right side responds similarly, although weaker, indicating that is most probably made of albite. FTIR-ATR analysis highlighted the structure of the compounds in the two areas. Calcite was identified both in the mortar binder and in the lumps.