Hydration Properties and Interlayer Organization in Synthetic C-S-H

Abstract

Water in calcium silicate hydrate (C-S-H) is one of the key parameters driving the macroscopic behavior of cement materials, for which water vapor partial pressure has a impact on the Young's modulus and the volumic properties. Several samples of C-S-H with bulk Ca/Si ratio ranging between 0.6 and 1.6 were characterized to study their dehydration/hydration behavior under water-controlled conditions, using 29 Si NMR, water adsorption volumetry, X-ray diffraction, and Fourier-transform near-infrared diffuse reflectance, under various water pressures. Coherent with several previous studies, it was observed that an increase in the Ca/Si ratio is due to the progressive omission of Si bridging tetrahedra, with the resulting charge being compensated for by interlayer Ca and that water conditioning influences the layer-to-layer distance and the achieved NMR spectral resolution. Water desorption experiments exhibit one step toward low relative pressure, accompanied by a decrease in the layerto-layer distance. When sufficient energy is provided to the system (T ≥ 40 °C under vacuum) to remove the interlayer water, the shrinkage/swelling is partially reversible in our experimental conditions. A change in layer-to-layer distance of less than 3 Å is measured in the C-S-H between the wet and dried states. When the bridging SiO 2 tetrahedra are omitted, interlayer Ca interacts with layer O and water interacts with the cations and potentially with the surfaces. This structural organization is interpreted as a mid-plane monolayer of water in the interlayer space, this latter accounting for about 30 % of the volume of C-S-H particles.

Molecular Dynamics Analysis of Water Adsorption on Calcium Silicate Hydrate

“…It can be seen from Figure 4 that with an increase in the C/S ratio, the fraction of vacant site increases, especially when the C/S ratio < 1, it increases significantly. The simulation results are consistent with the results obtained by Sylvain Grangeon et al [29] who used 29 Si NMR, which again proves the reliability of the simulation results. At the same time, as the C/S ratio increases, the absolute value of the charge balance extent first decreases and then increases.…”

“…More water molecules will be embedded in the defective silicate chains, which will also lead to the rearrangement of the interlayer calcium atoms and spread to the nonbridging sites of the defective silicate chains. When C/S < 1, it is found that, at the same pressure, the number of adsorbed water molecules decreases with an increase in the C/S ratio, which is consistent with the experimental results [29]. In order to ensure the maximum density of the C-S-H, the number of Si atoms was kept certain when the model was created, and part of the free Ca atoms were deleted.…”

Reinforced concrete structures: A review of corrosion mechanisms and advances in electrical methods for corrosion monitoring

“…The role of confined water in C-S-H micropores was demonstrated through molecular dynamic simulation [34,35]. Because of these points, understanding the distribution of water in C-S-H and their thermodynamic and hydration properties is of prime importance when considering the strength and transfer properties of cement materials [36][37][38][39][40][41]. Nonetheless, all the hydrates must be considered as they play a role in the cement-paste properties.…”

An Atomistic Model Describing the Structure and Morphology of Cu-Doped C-S-H Hardening Accelerator Nanoparticles

“…Among them, the crystal structure of several polytypes have been resolved [ 49 , 50 , 51 , 52 , 53 ]; in particular, the tobermorite 11 Å [ 49 ] and the tobermorite 14 Å (or plombierite) [ 51 ] better reflect the crystalline counterpart of nanocrystalline and defective C-S-H produced by the hydration of Portland cement [ 29 ]. Indeed, C-S-H shows a variable layer-to-layer distance between 14 and 11 Å, depending on the Ca/Si ratio, with several ions and water molecules bound to the structure in the interlayer space [ 54 ]. Recent studies favor a continuous structural evolution between C-S-H types, spanning the entire Ca/Si range, based on a tobermorite structural model [ 19 , 21 , 23 , 24 , 31 , 54 , 55 ], rather than a two-phase model based on the occurrence of tobermorite and jennite to describe C-S-H at low (<c.a.…”

“…Indeed, C-S-H shows a variable layer-to-layer distance between 14 and 11 Å, depending on the Ca/Si ratio, with several ions and water molecules bound to the structure in the interlayer space [ 54 ]. Recent studies favor a continuous structural evolution between C-S-H types, spanning the entire Ca/Si range, based on a tobermorite structural model [ 19 , 21 , 23 , 24 , 31 , 54 , 55 ], rather than a two-phase model based on the occurrence of tobermorite and jennite to describe C-S-H at low (<c.a. 1.3) and high (>c.a.…”