Infrared and Raman vibrational modelling of β-C2S and C3S compounds

Abstract

Density Functional Theory was applied to obtain a refined IR and Raman theoretical vibrational spectra of the major silicate phases of Portland cement, i.e. dicalcium silicate (β-C2S) and tricalcium silicate (C3S). We investigate the crystal structure and vibrational frequency values in the electronic ground state using a plane wave density functional method with new norm-conserving pseudopotentials. The calculated results show that the optimized geometry can reproduce the crystal structure well, and the theoretical vibrational frequency values show good agreement with the experimental values and allow us to describe some uncertainties in the experimental assignments previously described. The assignment performed for 100–1200 cm−1 region shows that the vibrations of C2S and C3S are presented in the IR spectra, while the vibrations with a minor contribution from the silica groups are observed in the Raman spectra. Satellite bands from C3S are observed in the experimental spectra but there not in the calculated one.