The effects of graphene oxide-silica nanohybrids on the workability, hydration, and mechanical properties of Portland cement paste

Although graphene-based materials have attracted much attention as nanoreinforcements for cementitious materials, their effectiveness is significantly dependent on their dispersibility in cement matrix. In particular, graphene hybridization (e.g. with silica) has shown considerable potential to meet this challenge within the broader family of graphene-based materials. In this study, we investigated the effects of silica coated graphene oxide (GOS) nanohybrids on the workability and the mechanical and microstructure properties of Portland cement paste composites. GOS with three different thicknesses of silica coating (5, 10 and 30 nm) were designed via a sol-gel method and characterized using microscopic techniques. We found that the increase in thickness of silica coating resulted in reduced workability of cement paste and a corresponding increase in cement mechanical properties with nanohybrid addition. With the incorporation of GOS, the compressive strength of cement paste was increased by 3.2–34.6% at 7 days and by 7–12.4% at 28 days, proportional to the increasing coating thicknesses. X-ray diffraction and mercury intrusion porosimetry indicated that the reaction of portlandite with the silica coating of the GOS nanohybrids led to pore refinement of the cement matrix, with more pronounced effects in samples with thicker coatings. These results demonstrate that rational design of graphene oxide nanohybrids presents an effective method to obtain stronger and more durable Portland cement composites.