Interfacial bonding between graphene oxide and calcium silicate hydrate gel of ultra-high performance concrete

Abstract

The incorporation of graphene oxide (GO) into ultra-high performance concrete (UHPC) can solve the problems of brittle fracture and low tensile strength of UHPC to some extent. By means of molecular dynamics simulation, this paper provided an insight into the interfacial bonding between GO and calcium silicate hydrate (C-S-H) gel, the dominant component of bonding phase in cement-based materials, in the chemical environment of UHPC in terms of C-S-H/GO interfacial structure, energies, and mechanical properties and gave the comparison with the case of ordinary Portland cement (OPC) materials. The results show that, as compared with the case of OPC, the C-S-H produced in UHPC has more calcium and hydroxyls distributed in the interlayer, leading to larger interlayer spacing with more water molecules absorbed. Water and hydroxyls occupy the sites of interfacial chemical bonds and weakens the C-S-H/GO interfacial Ca–O ionic bonds and H-bond network, but serve as bridges connecting C-S-H gel and GO sheet. More interlayer calcium for the UHPC case leads to larger interfacial interaction energies, which results in the higher tensile strength of the C-S-H/GO interface of UHPC sample. During tensile process, water molecules in the interface deforms with the structure and forms H-bond network serving to C-S-H/GO adhesion, which improves ductility of the structure. Furthermore, the configuration during elongation that the edge of GO sheet is tightly attached to C-S-H indicates the strong strength of Ca–Ocoo− bonds.