Effects of graphene oxygen content on durability and microstructure of cement mortar composites

Graphene materials have been extensively explored and successfully used to improve the properties of cement-based composites. However, current studies mainly focus on optimizing additional amounts and dispersion modes of graphene. The influence of other parameters, such as graphene crystallinity, size, and oxygen-containing functional group level, on the performance of cement mortar composite is not fully understood. Therefore, in this study, a series of reduced graphene oxides (rGO) with different oxygen concentrations were synthesized by controlling two parameters, namely, different concentrations of l-Vitamin C (10, 20, 50, and 70 wt%) and different reduction times (15, 30, 45, and 60 min), and added to the cement-mortar composite at the same dosage. The effect of rGO with different oxygen concentrations on the durability and microstructure of the composites was investigated. The durability results revealed that rGO with mild oxygen group level (i.e., prepared by 50 % l-Vitamin C reduction for 30 min) can remarkably enhance the durability of cement mortar composite material. Adding 0.1 wt% rGO with mild oxygen concentration to the cement mortar caused the initial water absorption and secondary water absorption to decrease by 44.75 % and 31.95 %, respectively, compared with ordinary cement mortar. This enables rGO/cement-mortar composites to have outstanding resistance in harsh erosive environments (i.e., high concentrations of CO2) because rGO promotes the cement hydration reaction and generates more hydration products. Meanwhile, the mild oxygen acid groups on the surface of the rGO act as a neutralizer in a strong alkaline medium, resulting in the formation of calcium carbonate precipitation, which further improves the compactness of the matrix.