*3.5. ATR Spectroscopy*

ATR spectra of the newly formed materials in the cracks are displayed in Figures 8 and 9. All the systems that were cured in water immersion presented aragonite and calcite peaks. The bands at 690 cm<sup>−</sup>1, 855 cm−1, 1082 cm−<sup>1</sup> and 1456 cm−<sup>1</sup> are bond vibrations of aragonite [29]. The calcite bond vibrations correspond to ~1400 cm<sup>−</sup>1, 875 cm−<sup>1</sup> and 712 cm−<sup>1</sup> [29]. The band of carbonates (Figure 8) has its maxima at 1456 cm−<sup>1</sup> (aragonite) but is broad and includes the CO3 <sup>−</sup><sup>2</sup> response of calcite at 1400 cm<sup>−</sup>1. The asymmetric stretching vibration of Si-O-M responses between 900–1100 cm−<sup>1</sup> [30], where M is a

metal cation. At 1003 cm<sup>−</sup>1, the response of calcium silicate is possible in the healing material of the nano-modified systems. In the reference healing material (Rw), this band was not observed.

**Figure 8.** ATR spectra of the healing material obtained from the crack of the samples cured in water immersion.

**Figure 9.** ATR spectra of the healing material obtained from the crack of the samples cured under wetting-drying cycles.

Under wetting-drying cycles (Figure 9), the reference healing material and the healing material from combined nanoparticles showed similar behavior with the water immersion healing materials. Aragonite and calcite presence prevailed in the newly formed material, though the presence of calcium silicate products is possible for NSLc. The addition of NC led to the formation of calcite rather than aragonite. The cycles have played a crucial role in the precipitation of the calcium carbonates in this case. The band at 1398 cm−<sup>1</sup> corresponds to carbonates. As for the silicate compounds, their band is shifted to 1017 cm<sup>−</sup>1.
