## 3 Results and Discussion
### Characterization of AC Waste
#### 3.1.3 Fourier Transform Infrared (FTIR) Spectroscopy and X-ray Diffraction (XRD) Study of AC Waste  
Fourier transform infrared (FTIR) spectroscopy was used for the identification of asbestos fibers in the AC sample. Chrysotile as a hydroxylated magnesium silicate has a structure consisting of brucite octahedral sheets linked to tetrahedral sheets of silica, producing layers of the 1:1 group minerals. Figure 5 shows FTIR spectra of the asbestos-cement sample. The main characteristic of the spectra of chrysotile is the presence of two bands at 3686 cm\({}^{-1}\) (strong) and 3638 cm\({}^{-1}\) (very weak) attributed to the stretching vibrations of the surface hydroxyl groups (crystallographically distinct) of the Si-OH and Mg-OH sheets in the chrysotile structure [53; 54]. The chrysotile OH stretching mode at around 3690 cm\({}^{-1}\) was also identified in the asbestos waste [55]. The peaks at 3452 and 1630 cm\({}^{-1}\) correspond to water molecules adsorbed into the chrysotile tubes. As shown in [56], Si-O stretching vibrations in asbestos minerals are reflected by the strong absorption band at the 1200-900 cm\({}^{-1}\) and 600-900 cm  
Figure 4: SEM micrographs of surface morphology of the asbestos–cement sample and map of the areal distribution and relative proportion (intensity) of all and the selected elements (Si, Ca, Mg, Al, K) over the scanned area (magnification 31 times). due to the vibration of the silicate chain, and the Si-O bending vibration. The broad band located between 1100 and 900 cm\({}^{-1}\) with a maximum at 1076, 1022 and 959 cm\({}^{-1}\) represents the symmetric stretching vibrations of Si-O-Si and Si-O bonds in SiO\({}_{4}\)\({}^{-4}\). In addition, O-H bending vibrations were observed in the 950-600 cm\({}^{-1}\) region. A broad O-H bending band is also present at 605 cm\({}^{-1}\). The absorption bands centered at about 1449 and 876 cm\({}^{-1}\) are due to the modes of the carbonate ions. Peaks centered at 1150 and 700 cm\({}^{-1}\) could be attributed to the vibrations of the bonds in SO\({}_{4}\)\({}^{-2}\)[55]. The bands at 605, 432 and 402 cm\({}^{-1}\) are assigned to stretching of Mg-O and/or of Mg-OH bending vibrations [54]. The typical band attributed to Mg-OH in brucite at 627 cm\({}^{-1}\) probably could be included in the wide band with a maximum intensity at 605 cm\({}^{-1}\). These bands observed at given wave numbers are in good accordance with the results in [57,58]. The presence of silicates, carbonates, and sulfates is obviously related to the cement matrix. Figure 6 shows the XRD pattern of the powder sample of asbestos-cement. The diffraction peaks correspond to the crystalline phases present in the cement matrix, and to the asbestos mineral chrysotile. The most intense two diffraction lines are assigned to presence of clinochrysotile (Mg\({}_{3}\)Si\({}_{2}\)O\({}_{5}\)(OH)\({}_{4}\), JCPDS no. 27-1275) at a basal d\({}_{\rm hld}\)-spacing of 7.33 A (20 angle of 12.07) and 3.65 A (20 = 24.37) (see Table 4). Other crystalline phases (calcium carbonates, and calcium silicates) originating from the cement matrix were found: (i) aragonite (CaCO\({}_{3}\), JCPDS no. 41-1475); (ii) calcite (CaCO\({}_{3}\), JCPDS no. 01-0837); (iii) vaterite (CaCO\({}_{3}\), JCPDS no. 33-0268); (iv) alite (Ca\({}_{3}\)SiO\({}_{5}\), JCPDS no. 49-0442); (v) larnite (Ca\({}_{2}\)SiO\({}_{4}\), JCPDS no. 29-0371). The presence of hydration products such as portlandite, calcium silicate hydrates, calcium aluminate hydrates, ettringite, and calcium monosulfoaluminate formed in a long-term hardened asbestos-cement sample was not identified. By calculating the crystallinity of the asbestos cement sample through Diffrac.EVA v4.2.2 software in the range of 10-80\({}^{\circ}\) 20, it was found that the sample contained only 30% of the crystalline phase and up to 70% of the amorphous phase. As is known, the main hydration cement products--calcium silicate hydrates (CSH phases)--are amorphous in nature with more complicated composition, therefore they were not observed on XRD pattern as expected.