Atomistic simulations of water-driven structural and mechanical changes in N–A–S–H gels

Abstract

This study employs molecular dynamics simulations to investigate the effect of varying water content (0–25 wt.%) and Si/Al ratio (1–3) on the atomistic structure and elastic properties of sodium aluminosilicate hydrates (N–A–S–H) gels. Results show that water molecules break the aluminosilicate framework by forming hydroxyl groups on AlO₄ and SiO₄ units. It induces the release of sodium from its charge-balancing role, which in turn solubilizes in water. The framework unfolds while the pores are progressively filled by water, and it leads to depolymerization. The elastic properties are therefore largely affected. In one hand, the framework of the gels and the filling of the pores by water control the evolution of the bulk modulus. On the other hand, subtle effects included in the density, where porosity and its saturation, density of the dry framework, and Si/Al ratio appear together, drive the Young's modulus.