▎ 摘　　要

The investigations on reduced graphene oxide (rGO) or graphene as an additive for cement reinforcement is relatively limited. Previous studies either employed thick graphene nanoplates, obscuring the flexible nature of graphene, or involved toxic agents, hindering their practical applications. Interestingly, in spite of the importance of uniform dispersion, there is still no method for quick and effective evaluation of the dispersion quality of rGO in both water and pore solution. Here, we prepare high-quality rGO by green chemical reduction of graphene oxide, followed by thorough washing without drying. The dispersion quality of rGO was assessed by dynamic light scattering, transmission electron microscopy, as well as morphological characterization of rGO film prepared by filtration. Because of water depletion by cement hydration, rGO agglomeration in pore solution is inevitable even for 0.05 wt% rGO/cement nanocomposites. This work shows that the compressive and flexural strength of a cement paste at 28 days were enhanced by 16.5% and 20.9% by admixing 0.05 wt% rGO, corresponding to very high reinforcement efficiency of 330% and 418%, respectively. Interestingly, the extremely low concentration (0.01 wt%) of rGO resulted in a decrease of flexural strength of cement paste. This is probably attributable to the flexibility of rGO nanosheets, which allows rGO to conformally wrap cement particles and affect its hydrated microstructure. Therefore, a minor level of rGO agglomeration is likely beneficial to the effective reinforcement of cementitious material by rGO, and the effect of nanosheets encapsulating the reactive particle or its matrix should be considered.