Graphene and graphene oxide in calcium silicate hydrates: Chemical reactions, mechanical behavior and interfacial sliding

Abstract

We investigate chemical reactions, mechanical behaviors and interfacial sliding of calcium silicate hydrates (CSH) incorporating graphene nanosheet (GNS) and graphene oxide (GO) containing epoxides (GO-Oo) and hydroxyls (GO-OH) through molecular dynamics simulation. Structural analysis reveals that chemical reactions occur at the interface between GO and CSH matrices because the alkaline environment in CSH provides Ca2+ coordination and hydrogen bonds with GO. The Young's modulus and strength of CSH are enhanced by 52.6% and 23.3% with the incorporation of GO-OH while an increase of 31.6% and 17.5% in Young's modulus and strength is achieved by incorporating GO-Oo, attributed to high interfacial interaction energy and mechanical interlocking. However, GNS can hardly enhance the mechanical properties of CSH because its 2D surface has no interlocking with the matrix. The pull-out test reveals that mechanical interlocking plays a decisive role in the enhancement of the interfacial shear strength. During the pull-out process, functional groups are exfoliated from GO, which is harmful to its reinforcing ability. This study provides, for the first time, valuable insight into interfacial reaction mechanisms and working mechanisms of GNS/GO in realistic CSH structure.