Effect of temperature on the capillary transport of sodium sulfate solution in calcium silicate hydrate nanopore: A molecular dynamics study

FJ Wang and Y Zhang and JY Jiang and B Yin and ZJ Li, CONSTRUCTION AND BUILDING MATERIALS, 231, 117111 (2020).

DOI: 10.1016/j.conbuildmat.2019.117111

This paper gives a new sight into the effect of raised temperature on the capillary transport and interaction of sodium sulfate with calcium silicate hydrate (C-S-H). Molecular dynamics is utilized and temperature parameters are set as 300, 330, 360, and 390 K, respectively. Elevated temperature promotes the transport of water in the nanometer C-S-H channel, however, the transport rate of sodium and sulfate ions in the channel is significantly reduced as a result of the formation and adsorption of ionic clusters on C-S-H channel. This unexpected phenomenon can be explained by three factors. Under elevated temperature, first, hydration shell of ions is weakened and thus increasing the probability of ion-ion and ion substrate contact. Second, more calcium is dissociated from C-S-H channel and resulting in the formation and precipitation of calcium sulfate, the precursor of gypsum. Third, the local structure of C-S-H channel is changed under elevated temperature, such as the dissociation of calcium from C-S-H channel, the strong stretching vibration of Si-Os bond and surficial hydroxyls, and increases in mean bond length of surficial hydroxyls. All of these increase the chemical activity of partial oxygen sites on C-S-H channel surface, contributing to more aqueous sodium ions adsorbed on C-S-H surface by electrostatic attraction from surficial oxygen. (C) 2019 Elsevier Ltd. All rights reserved.

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