Raman spectroscopy of C-S-H, tobermorite, and jennite

Abstract

Raman spectra of single-phase calcium-silicate hydrate (C-S-H) samples with C/S ratios between 0.88 and 1.45 are consistent with a defect tobermorite model for the structure of these materials, in agreement with previously published nuclear magnetic resonance (NMR) spectroscopic data for the same samples. The Raman spectra of C-S-H samples with C/S ratios <1.0 are very similar to those of 14Å tobermorite. Those of C-S-H samples with C/S ratios ⩾1.0 show substantial concentrations of both Q¹ and Q² Si sites and indicate the possible presence of jennite-like environments. Raman spectroscopy, like infrared and NMR, is a probe of local structure on the atomic nearest neighbor and next-nearest neighbor scale, and thus provides significantly different information than diffraction methods. The Raman spectra of the C-S-H have a rich structure and contain peaks for Si-O stretching, Si-O-Si bending, internal deformation of the Si-O tetrahedra and Ca-O polyhedra, and characteristic peaks at lower frequencies. The spectra of jennite and 14Å tobermorite are quite similar, confirming the result from NMR spectroscopy that jennite has dominantly Q² polymerization. The Raman spectra of 11Å and 14Å tobermorite are also similar, although our sample of 11Å tobermorite has a significant concentration of Q³ Si sites, which indicates cross-linking of the chains.