The effects of carbonation of mechanochemically prepared C-S-H samples under ambient conditions for upto 6 months have been investigated by Raman spectroscopy and X-ray diffraction. The type and extent of carbonation are strongly dependent on the initial CaO/SiO 2 (C/S) ratio of the samples. Amorphous calcium carbonate hydrate is formed within minutes upon exposure to air. It crystallizes, over time, to give primarily vaterite at C/S ! 0.67 and aragonite at C/Sr0.50. Calcite was not observed as a primary carbonation product within the time frame investigated. Decalcification upon storage also initiates silicate polymerization. The dimeric silicate units seen in the calcium-rich phases polymerize rapidly to yield Q 2 silicate moieties. After 6 months, broad bands are seen in most spectra, ascribed to poorly ordered silica. C-S-H phases with C/S ratios of 0.75 and 0.67 are the most resistant to carbonation, and even after 6 months of storage, Q 2 silicate units still dominate their structures. The ability of Raman spectroscopy to probe the short-range order of poorly crystalline materials is ideal for investigations of C-S-H structure. Additionally, the technique's sensitivity toward the various calcium carbonate polymorphs illuminates the sequence of carbonation and decalcification processes during aging of C-S-H. Of particular importance is the identification of amorphous calcium carbonate as the first carbonation product. Additionally, the formation of aragonite as a carbonation product is related to the presence of SiO 2 gel in the aged samples.G. Scherer-contributing editor

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 reveal changes in structure with changes in the C/S ratio. These support 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 À1 . 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 B1401. Finite silicate chains (Q 2 ) dominate the structures of the samples at C/S ratios 0.2-1.0, the spectra showing characteristic bands from 1010 to 1020 cm À1 . When the samples are measured in air, the spectra exhibit carbonate bands arising from surface carbonation. The n 1 [CO 3 ] bands obscure the characteristic Raman scattering of silicate units near 1080 cm À1 , which is clearly evident in the fresh samples analyzed in closed capillaries. At C/S41.00, dimers (Q 1 ) are the main building unit of the silicate anionic structure, with a characteristic band at 889 cm À1 . At C/S ratios 1.33 and 1.50, portlandite (Ca(OH) 2 ) is also observed.G. Scherer-contributing editor

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We report a systematic FTIR study of the perturbation of water “sorbed” into the polymers PET and PVC as a function of crystallinity (PET) or plasticizer content (PVC). Band shapes of the composite ν(OH) band of H2O obtained by the ATR technique have been fitted to individual components,corresponding to those recently found for pure water itself. A detailed quantitative analysis of the frequency shifts and relative intensties has led to conclusion that these component bands show direct evidence for the breaking of the water network in the polymer matrix and that this process depends on the polymer chemical and/or physical properties. Evidence is also found for interactions of water with the polymer at the lower end of the hydrogen bond interaction scale. The component band relative intensities (compared with those of pure water) have been used to compute an intensity enhancement parameter, P, which is a measure of the perturbation of a particular water distribution due to dissolution in the polymer matrix. For PET, P varies systematically with density, reflecting the ability of water to penetrate the polymer microstructure. For PVC the plasticizer content (and hence T g) has a considerable influence on the sorption (and swelling) process and on the equilibrium content and state of water. Thus, ATR-FTIR has been used for the first time to demonstrate,via intensity enhancement, the extent of electronic perturbation at a polymer/water interface.