STRUCTURAL FEATURES OF C-S-H(I) AND ITS CARBONATION IN AIR - A RAMAN SPECTROSCOPIC STUDY. PT.1. FRESH PHASES

The Raman spectra of a series of mechanochemically prepared calcium silicate hydrate samples of type C-S-H(I) with C/S ratios ranging from 0.2 to 1.5 revealed changes in structure with changes in the C/S ratio. This supports the model of Stade and Wieker based entirely on the tobermorite structure. The main characteristic feature of the spectra is the Si-O-Si bending vibration at about 670 cm-1. Comparisons with bending frequencies of some known crystalline phases composed of single silicate chains led to an estimation of the mean Si-O-Si angles in the C-S-H(I) phases to be about 140 degrees. Finite silicate chains (Q2) dominate the structures of the samples at C/S ratios 0.2-1.0, the spectra showing characteristic bands from 1010 to 1020 cm-1. When the samples were measured in air, the spectra exhibited carbonate bands arising from surface carbonation. The nu1[CO3] bands obscured the characteristic Raman scattering of silicate units near 1080 cm-1, which was clearly evident in the fresh samples analysed in closed capillaries. At C/S > 1.00, dimers (Q1) were the main building unit of the silicate anionic structure, with a characteristic band at 889 cm-1. At C/S ratios 1.33 and 1.50, portlandite (Ca(OH)2) was also observed. 70 refs.