PSI - Issue 67

I. Flores-Vivián et al. / Procedia Structural Integrity 67 (2025) 80–89 Ismael Flores-Vivián/ Structural Integrity Procedia 00 (2024) 000 – 000

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Figure 7 . Comparison of FT-IR spectra of precursors vs pastes added with a) natural zeolite ZN, b) zeolite NaY

The band located at 1058 cm -1 in the MK is attributed to Si-O bonds, the displacement of this band to lower frequencies indicates the dissolution of these bonds and the formation of new aluminum-rich phases (Belmokhtar, Ammari, Brigui, & Allal, 2017 ). This displacement is evident when comparing the position of the initial band in the MK and in the zeolites 1034 cm -1 and 994 cm -1 , for ZN and NaY, respectively, against the position of the pastes after hydration, 867 cm -1 , 862 cm -1 , 854 cm -1 in R10, ZN10 and ZY10, respectively. However, there is no appreciable difference in band positions between 3- and 7-day-old pastes. On the other hand, this band becomes more pronounced as the polycondensation process progresses, which can be observed in ZN10 and ZY10 pastes compared to reference pastes (Ming, Yong, Bakri, & Hussin, 2016). The band close to 780 cm -1 found in the MK is attributed to the stretching of the Si-O-Si/Si-O-A groups, it is displaced to 720 cm -1 and with less intensity in the pastes. In the spectra belonging to zeolites ZN and NaY, the band 600 cm -1 , assigned to the symmetrical stretching of the internal tetrahedra of SiO 4 and AlO 4 , in geopolymers can reach frequencies up to 460 cm -1 (Ahmedzeki, Yilmaz, & Al-Tabbakh, 2016) (Yun Ming, Cheng-Yong, Bakri, & Hussin, 2016). 3.2.2. Influence of NaOH molarity Figure 8 shows the FT-IR spectra of pastes with 7M and 12M NaOH concentrations, which are compared to observe the effect of the increase in the molarity of the AA. The presence of -OH ions increase the dissolution of Si O bonds, so a higher concentration of NaOH promotes a better dissolution of the silicoaluminous precursor (Provis & Deventer, 2009). This is reflected in a greater shift towards lower frequencies of the absorption bands of the Si-O bonds, previously mentioned, of pastes with a concentration of 12M, compared to those of 7M, as well as in both reference pastes and those with the addition of ZN. However, this was not observed in the ZY10 paste which, although this band is more pronounced than ZY7, does not show greater displacement as in the other pastes with molarity of 12. It is also possible to see the displacement of the band of the -OH groups towards lower frequencies, which may be due to an increase in the Si/Al (Chester & Derouane, 2009). 2.3. Scanning electron microscopy The SEM was used to compare the microstructure of the hydrated pastes and compare the effects of the addition of zeolites on the geopolymeric matrix. The micrographs of the R10, ZN10 and ZY10 pastes were compared at the age of 7 days, in Figure 9 the three pastes have a similar microstructure, amorphous particles with homogeneous distribution are seen.