FT-IR spectroscopy is employed to investigate the effect of the
local porosity, i.e., water to cement (w/c) ratio, at two different curing
times of 3 and 28 days on the bands spectra in the ordinary Portland
cement pastes (OPC) in the spectral range 400 to 4000 cm-1. The study
revealed the characteristic changes in the stretching and bending
vibration modes of the SiO4 group (≈ 460 cm-1), the stretching vibration
modes of the C-O and of C=O bonds (≈ 970 cm-1, and 1430 cm-1) (the
strong absorption of the 2-
3 CO group in the lattice region), and finally,
the stretching vibration of the water molecules (vibration of the OHgroup < br />of the Portland CH phase). The results have indicated that the
critical conditions for the change accompanying these vibration modes
during the hydration mechanism of the OPC samples occur at (w/c)
ratio of 0.3, and 0.35 independently of the hydration time.