Effect of graphene dispersion methods on mechanical and electrical properties of ultra-low-w/b cement pastes

This study investigates the influence of different dispersion methods of graphene nanoplatelets (GNPs) on the fluidity, mechanical, electrical, and microstructural properties of cement pastes with ultra-low water-to-binder (w/b) ratio of 0.18. Five dispersion strategies including ultrasonication (30 min and 60 min), mechanical stirring, and hybrid dispersion with silica fume (5% and 10%) were evaluated. Results reveal that extended ultrasonication for 60 min slightly reduced the initial fluidity but produced more stable time-dependent flow behavior due to the increased water adsorption on well-dispersed GNPs. Compared to the reference paste, the paste mixture after ultrasonication treatment for 60 min achieved the highest flexural and compressive strengths, as well as the most reduced electrical resistivity. This is possibly due to the fact that uniform GNP dispersion promotes crack bridging, nucleation of hydration products, and microstructural densification. Conversely, silica fume incorporation markedly improved early compressive strength through pozzolanic reactions and particle packing but significantly increased the electrical resistivity by disrupting conductive pathways. The findings highlight that dispersion efficiency is an important factor in maximizing the multifunctional potential of GNPs-containing cementitious composites, offering valuable insights for designing the next-generation high-performance self-sensing materials.