3.1.2. FTIR

The FTIR spectra of the cement and ground CDW can be seen in Figure 1. In the case of the raw cement spectrum, the transmittance bands at 1421, 874 and 713 cm−<sup>1</sup> can be assigned to v3, v2, and v4 stretching modes of CO3 <sup>2</sup>−, respectively. The weak band at 1124 cm−<sup>1</sup> is generally the indication of Si–O–Si stretching vibrations and the band at 521 cm−<sup>1</sup> corresponds to the Si–O deformation vibrations of the siliceous phases [22,23].

For the CDW samples, some new bands could also be observed compared to the cement sample. The broad band between ~3500–2800 cm−<sup>1</sup> corresponds to the stretching O–H, and the weak band at 1614 cm−<sup>1</sup> to the O–H bending mode, indicating the presence of a small amount of structural and weakly bound water in the samples. The bands centered between 1420–1450 cm−<sup>1</sup> and at 875 cm−<sup>1</sup> are associated with the calcite and other carbonate species. The broad band of 1010–1030 cm−<sup>1</sup> originates from the asymmetric stretching vibrations of the C–S–H structure that was originally formed in the cementitious matrix. The bands at 795 and 695 cm−<sup>1</sup> show the presence of quartz [20,24]. Comparing the spectra of the ground CDW samples, no significant changes occurred in the structure with the different milling times. After 3 min or longer mechanical activation, the intensity of the C–S–H band slightly increased and broadened, indicating the possible amorphization of the material.
