Silicate Bond Characteristics in Calcium-Silicate-Hydrates Determined by High Pressure Raman Spectroscopy

DW Gardner and JQ Li and A Morshedifard and S Masoumi and MJA Qomi and PJM Monteiro and R Maboudian and C Carraro, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 18335-18345 (2020).

DOI: 10.1021/acs.jpcc.0c04563

The mechanical and thermal properties of the gigatonnes of concrete produced annually are strongly affected by the anharmonicity of the chemical bonds in its main binding phase, nanocrystalline calcium-(alumino-)silicate-hydrate (C-(A-)S-H). Improvements in C-(A-)S-H design increasingly depend on simulations utilizing a set of effective interatomic forces known as "CSH-FF", yet these assumptions have never been directly examined at the chemical bond level, and there is no guidance for their improvement. In this work, we use high-pressure Raman spectroscopy to directly measure bond anharmonicity in a representative series of C-(A-)S-H samples with varying composition and two natural model minerals, 14 angstrom tobermorite and xonotlite. We find that structural water molecules effectively scatter thermal energy, providing a heuristic for improving the thermal resistance of concrete. A comparison of experimental and calculated bond anharmonicities shows that a stiffer Si-O interaction would improve the transferability of CSH-FF to the thermal properties of C-(A-)S-H. High-pressure Raman spectroscopy is suggested to improve the calculations of C-S-H and to characterize other complex, nanocrystalline materials.

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