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The application of waste rubber powder (WRP) for asphalt pavement could achieve the harmless and resourceful utilization of solid waste, but the storage stability of waste rubber powder modified asphalt (RA) is one of the main problems restricting its application. Existing studies have demonstrated that graphene could enhance the storage stability of RA, but graphene's size effect on the modifying effect and its corresponding mechanism are still uncertain. In this research, the effects of graphene microstructural properties (i.e., molecular size and layer number) on the storage stability of RA were investigated by storage stability testing, dynamic shear rheometry (DSR) testing and fluorescence microscopy (FM) testing, in combination with molecular dynamics simulation (MD). The experimental results indicated that graphene improved the storage stability of RA significantly, with few-layer graphene being more effective in enhancing it. MD was used to investigate the graphene size effect on RA in compatibility, intermolecular binding energy and structural stability of the system. The simulation results revealed that small-sized graphene molecules were more compatible with RA. Meanwhile, few-layer, small-sized graphene can provide higher binding energy and better enhancement of storage stability of RA. The number of graphene layers mainly influences the binding energy rather than solubility parameters. The relative concentration distribution results demonstrated that graphene facilitated the spatial distribution of asphaltenes, rubber components and light components. This research provides theoretical support for the rational selection of microstructural properties of graphene to improve the modified asphalt storage stability performance. [ABSTRACT FROM AUTHOR]

• The improvement of the rheological properties of asphalt by graphene was studied. • Using multiple-scale experiments combined with molecular dynamics simulation. • The focus is on the size effect of graphene on the modification efficiency. The use of waste rubber powder modified asphalt (RA) in road engineering can lead to environmental and economic benefits. However, there are still some concerns over the performance of the pavement with RA, especially the rheological properties under heavy traffic conditions. This paper aims to investigate the improvement effects of graphene on the rheological properties of RA using multiple-scale experimental characterizations combined with molecular dynamics simulation. Special attention was paid to the influence of geometric characteristics of graphene on the modification efficiency. The experimental findings demonstrated that the physical blending of graphene and RA could enhance viscoelasticity, persistent deformation, and mobility resistance of modified asphalt, while its low-temperature performances were marginally improved with the graphene. Graphene with a single layer or a few layers was more efficient in enhancing the high-temperature deformation and rutting resistance and microstructures of RA than that with multiple layers. The molecular dynamics simulation results showed that graphene could improve the shear viscosity of the modified asphalt and inhibit the diffusion of asphalt components, and the effect on the low-temperature performance is related to the size effect. Moreover, the size of graphene particles could strongly influence the performances of the modified asphalt. Specifically, increasing the graphene size decreased the shear viscosity, free volume fraction, and glass transition temperature, indicating the improved deformation resistance. The change in the number of graphene layers was more effective in altering the modification effect of small-sized graphene compared to large-sized graphene. This research can offer a theoretical guideline for optimizing the use of graphene in modified asphalt. [ABSTRACT FROM AUTHOR]