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Structural changes in C-S-H gel during dissolution: small-angle neutron scattering and Si-NMR characterization



Ana Trapote-Barreira, Lionel Porcar, Jordi Cama, J. M. Soler, Andrew J. Allen


Flow-through experiments were conducted to study the calcium-silicate-hydrate (C-S-H) gel dissolution kinetics under a CO2-free atmosphere at room temperature (22 ± 2) ºC in the pH range from 10 to 13 relevant to cement media. During C-S-H gel dissolution the initial aqueous Ca/Si ratio decreases to reach the stoichiometric value of the Ca/Si ratio of a tobermorite-like phase (Ca/Si = 0.83). As the Ca/Si ratio decreases, the solid C-S-H dissolution rate, based on Si release and normalized to the final Brunauer-Emmett-Teller (BET) specific surface area, increases from (4.5 x 10-14 to 6.7 x 10-12) mol m-2 s-1. The changes in the microstructure of the dissolving C-S-H gel were characterized by small-angle neutron scattering (SANS) and 29Si magic-angle-spinning nuclear magnetic resonance (29Si-MAS NMR). The SANS data were fitted using a fractal model. The SANS specific surface area (SSA) tends to increase with time and the obtained fit parameters reflect the changes in the nanostructure of the dissolving solid C-S-H within the gel. The 29Si MAS NMR analyses show that with dissolution the solid C-S-H structure tends to a more ordered tobermorite structure, in agreement with the Ca/Si ratio evolution.
Cement and Concrete Research


C-S-H gel, small-angle neutron scattering, nuclear magnetic resonance, cement dissolution, fractal models


Trapote-Barreira, A. , Porcar, L. , Cama, J. , Soler, J. and Allen, A. (2015), Structural changes in C-S-H gel during dissolution: small-angle neutron scattering and Si-NMR characterization, Cement and Concrete Research, [online],, (Accessed May 23, 2024)


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Created March 6, 2015, Updated October 12, 2021