Effects of sodium/calcium cation exchange on the mechanical properties of Calcium Silicate Hydrate (C-S-H)

Abstract

Calcium silicate hydrate layer (C-S-Hlayer) is considered to be the fundamental building block of hydrated cement. The effect of sodium ions on the atomic scale mechanical properties of C-S-Hlayer remains, however, unclear. Yet, this information is critical for understanding and predicting the macroscopic performance of concrete structures during their service life. Herein, the intrinsic mechanical properties of C-S-Hlayer with sodium-exchange ions replacing some calcium cations were studied by molecular dynamics simulations. The interatomic interactions provided insights into the role of Na+ within the atomistic scale of C-S-Hlayer. It was found that Na+ did not significantly alter the mechanical properties (i.e., strength and stiffness) of C-S-Hlayer. The larger cationic attraction on the interlayer water molecules seen in the presence of Na+ occurred due to the exchange of two Na+ for one calcium cation and resulted in a volume expansion of C-S-Hlayer while a stiffening of its interlayer.