Proposed mechanism for the enhanced microstructure of graphene oxide-Portland cement composites

Graphene oxide (GO) nanosheets can enhance the nanostructure of calcium silicate hydrate (C-S-H), the binder phase of Portland cement, and thereby increase the strength and durability of building materials. However, the mechanism underlying the observed enhancements remains to be elucidated, impeding the full realization of GO in the cementitious composites. Based on a comprehensive microscopy analysis of the effect of GO on C-S-H gel formed in tricalcium silicate cement, Portland cement, and synthetic systems, here we present a growth model that can explain the GO-induced improvements in the C-S-H nanostructure. It is proposed that GO nanosheets function as two-dimensional platforms to promote the growth of C-S-H gel via the Stranski-Krastanov (island-on-wetting-layer) growth mode. This growth mode can account for the formation of C-S-H with compact nanostructure leading to the cement matrix densification that has been widely reported in the literature. Through reconciliation with well-established descriptions of C-S-H gel, the proposed model can rationalize the superior mechanical and durability properties of cement building materials containing GO and other 2D nanomaterials.