Full process of calcium silicate hydrate decalcification: Molecular structure, dynamics, and mechanical properties

Abstract

C-S-H gel is the origin of cohesion of cement and deteriorates with decalcification. However, the molecular process underlying its complex chemical reactions and structure/properties evolution is mostly unexplored. Herein, the influence of decalcification on calcium silicate hydrate (C-S-H) is studied by molecular dynamics and experiments. The results show, during the decalcification, the transformation of C-S-H molecular structure from lamellar crystal into cross-linked glassy structure, transformation from bound water into -OH groups, and transformation of dynamics characteristics from lattice vibration at fixed sites into diffusion, which would be exacerbated by the dissociation of intralayer calcium. Mechanically, for both nano and micro/macro scale, tensile property of C-S-H depends on interlayer bonding and so is weakest at complete dissociation of interlayer calcium, whereas compressive property decreases continuously with decalcification. The interlayer bonding basically determines the threshold of micro/macro mechanical properties of C-S-H gel. This study provides a well example for molecular-scale exploration of the full process of aluminosilicate mineral dissolution.