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

Published

March 7, 2015

Author(s)

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

Abstract

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.

Citation

Cement and Concrete Research

Volume

72

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.cemconres.2015.02.009

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Keywords

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

Citation

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], https://doi.org/10.1016/j.cemconres.2015.02.009, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=916312 (Accessed April 29, 2024)