Tribological characterization of graphene nano-platelet (GNP) bituminous binders

According to recent research, the addition of graphene nano-platelets (GNPs) to bitumen can lead to a considerable improvement of the compactability of bituminous mixtures, without reducing the viscosity of the binder, meaning that other mechanisms are responsible for this phenomenon. In this regard, the present study focuses on the characterization of the lubricating behaviour of GNP binders obtained by adding 3% and 6% GNPs to a plain PG 58-28 bitumen, through a novel tribological approach recently proposed in literature. In addition, the experimental program is completed by viscosity tests. Results show that GNP addition leads to an increase in both viscosity and friction, which in general is greater for higher GNP contents, for all testing temperatures. A good correlation between viscosity and minimum friction exists in the elasto-hydrodynamic regime of lubrication, whereas the results obtained in the boundary and mixed regimes may be significantly affected by the testing conditions considered. Specifically, the use of different substrates is suggested for future work, in order to achieve a better understanding of the mechanisms that govern the compaction behaviour of bituminous mixtures.