Extended X‐ray Absorption Fine Structure Investigation of Calcium Silicate Hydrates

Lequeux, Nicolas; Morau, Alain; Philippot, S.; Boch, P.

doi:10.1111/j.1151-2916.1999.tb01911.x

Cited by 46 publications

(64 citation statements)

References 38 publications

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“…In both cases, the mean chain length increases with decreasing Ca/Si ratio, in agreement with previous 29 Si NMR studies [3,4,[16][17][18][19][20]. However, for Ca/Si ratios above 1, there is a small but significant difference between the two preparations, as the mean chain lengths of the samples from the C 3 S group are consistently higher than those from the double decomposition group.…”

Section: Si Nmrsupporting

confidence: 91%

“…Single dreierketten have been confirmed by 29 Si NMR and by trimethylsilylation (TMS), the latter showing that the removal of bridging tetrahedra fragments the infinite silicate chains into segments containing 2, 5, 8,…(3n-1) tetrahedra [13][14][15]. The mean chain length, measured by 29 Si NMR, increases with decreasing Ca/Si ratio, particularly below a Ca/Si ratio of 1.1-1.3 [3,4,[16][17][18][19][20].…”

Section: Less-crystalline Phases: C-s-h(i) C-s-h(ii) and C-s-h Gelmentioning

confidence: 98%

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Solubility and structure of calcium silicate hydrate

Chen

Thomas

Taylor³

et al. 2004

Cement and Concrete Research

721

414

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C-S-H, the poorly crystalline calcium silicate hydrate formed in cement paste and aqueous suspension, is characterized by extensive disorder and structural variations at the nanometer scale. An analysis of new and published solubility data for C-S-H formed by different preparation methods and with a broad range of compositions illustrates a previously unrecognized family of solubility curves in the CaO-SiO 2 -H 2 O system at room temperature. As demonstrated by 29 Si magic-angle spinning (MAS) NMR data and by charge balance calculations, the observed differences in solubility arise from systematic variations in Ca/Si ratio, silicate structure, and Ca-OH content. Based on this evidence, the family of solubility curves are interpreted to represent a spectrum of metastable C-S-H phases whose structures range from purely tobermorite-like to largely jennite-like. These findings give an improved understanding of the structure of these phases and reconcile some of the discrepancies in the literature regarding the structure of C-S-H at high Ca/Si ratios.

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Section: Si Nmrsupporting

confidence: 91%

Section: Less-crystalline Phases: C-s-h(i) C-s-h(ii) and C-s-h Gelmentioning

confidence: 98%

Solubility and structure of calcium silicate hydrate

Chen

Thomas

Taylor³

et al. 2004

Cement and Concrete Research

721

414

View full text Add to dashboard Cite

show abstract

“…For instance, the simulated and experimental Ca total pair distribution functions as measured in EXASF (Fig. 2 A), agree well, showing peaks at the same inter-atomic distances with same relative intensities that allow discriminating C-S-H against all other calcio-silicate crystalline solids (12). The fact that the first peak in the experimental EXAFS signal is broader than that obtained in simulation suggests that real C-S-H may exhibit an even larger volume fraction of short-range structural disorder.…”

supporting

confidence: 55%

A realistic molecular model of cement hydrates

Pellenq

Kushima²,

Shahsavari³

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

787

533

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Despite decades of studies of calcium-silicate-hydrate (C-S-H), the structurally complex binder phase of concrete, the interplay between chemical composition and density remains essentially unexplored. Together these characteristics of C-S-H define and modulate the physical and mechanical properties of this ''liquid stone'' gel phase. With the recent determination of the calcium/silicon (C/S ‫؍‬ 1.7) ratio and the density of the C-S-H particle (2.6 g/cm 3 ) by neutron scattering measurements, there is new urgency to the challenge of explaining these essential properties. Here we propose a molecular model of C-S-H based on a bottom-up atomistic simulation approach that considers only the chemical specificity of the system as the overriding constraint. By allowing for short silica chains distributed as monomers, dimers, and pentamers, this C-S-H archetype of a molecular description of interacting CaO, SiO2, and H2O units provides not only realistic values of the C/S ratio and the density computed by grand canonical Monte Carlo simulation of water adsorption at 300 K. The model, with a chemical composition of (CaO)1.65(SiO2)(H2O)1.75, also predicts other essential structural features and fundamental physical properties amenable to experimental validation, which suggest that the C-S-H gel structure includes both glass-like short-range order and crystalline features of the mineral tobermorite. Additionally, we probe the mechanical stiffness, strength, and hydrolytic shear response of our molecular model, as compared to experimentally measured properties of C-S-H. The latter results illustrate the prospect of treating cement on equal footing with metals and ceramics in the current application of mechanism-based models and multiscale simulations to study inelastic deformation and cracking.atomistic simulation ͉ mechanical properties ͉ structural properties B y mixing water and cement, a complex hydrated oxide called calcium-silicate-hydrate (C-S-H) precipitates as nanoscale clusters of particles (1). Much of our knowledge of C-S-H has been obtained from structural comparisons with crystalline calcium silicate hydrates, based on HFW Taylor's postulate that real C-S-H was a structurally imperfect layered hybrid of two natural mineral analogs (2) (4)]. While this suggestion is plausible in morphological terms, this model is incompatible with two basic characteristics of real C-S-H; specifically the calcium-tosilicon ratio (C/S) and the density. Recently, small-angle neutron scattering measurements have fixed the C/S ratio at 1.7 and the density at 2.6 g/cm 3 (1), values that clearly cannot be obtained from either tobermorite (C/S ϭ 0.83, 2.18 g/cm 3 ) or jennite (C/S ϭ 1.5 and 2.27 g/cm 3 ). From the standpoint of constructing a molecular model of C-S-H, this means that these crystalline minerals are not strict structural analogs. Here we adopt the perspective that the chemical composition of C-S-H is the most essential property in formulating a realistic molecular description. We show that once the C/S ratio is described...

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“…The maps show sharp peaks, corresponding to the position of atoms of the structure (empty circles), and smooth cavities with only few contour lines, corresponding to ideal atom positions, i.e., where the valence sum of Nd is at or close to its nominal valence +3 [31]. [32]. The DW factor was found to vary between 0.008 ± 0.001 Å 2 and 0.014 ± 0.002 Å 2 in most cases.…”

Section: Bond-valence Approachmentioning

confidence: 99%