Additionally,
a relatively well resolved band at 653–717 cm
1
appeared
which is associated to the symmetric stretching vibrations of
Si–O–Al bridges. The absorption band located at 1631–
1637 cm
1
is due to bending H–O–H vibration and the absorption band at 3436–3452 cm
1
is due to stretching of O–H
groups; This band disappeared in anhydrous GBFS due to
the absence of hydration products such as C–S–H or
C–A–H. The absorption bands of water are an indication to
crystalline H2O of the hydrated products such as C–S–H and
C–A–H[35]. The absorption bands located at 988–970 cm
1
are due to Si (Al)–O asymmetric stretching vibrations. The
high full width at half maximum (FWHM) of this band of
anhydrous GBFS is wider than that of GBFS-dry activator
blends. It is known that phases of non-ordered structure
increase the band width due to the existence of significant
fluctuations of geometric parameters, i.e.,