Investigation of graphene additive performance in hot mix asphalts

The most widely used type of pavement is flexible pavement, in which bitumen is used as a binding material due to its many advantages. Hot mix asphalt pavements (HMA) are often preferred for the safety, comfort, economy and sustainable roads expected from transportation. However, different deteriorations occur in HMA pavements due to traffic, climate, and environmental effects. Bitumen is modified with different additives to make the pavements more resistant to these deteriorations. In this study, graphene nanoplatelet (GNP) was used as an additive material due to its strength, flexibility, and cost-effectiveness. According to the experimental plan determined by the Taguchi method, 0; 0.35; 0.70; 1% GNP rates; 145, 160, 175, 190°C mixing temperatures; 15, 30, 45, 60 minutes mixing times; 1000, 2000, 3000, 4000 rpm mixing speeds, 16 different mixtures were prepared using four parameters and four levels each. Penetration, softening point, flash point, elastic recovery, rotational thin film heating loss (RTFOT), Fourier transform infrared spectroscopy (FT-IR), and Marshall design experiments were conducted on these mixtures, and the effects of the determined parameters and levels on bitumen were investigated. As a result of the study, the GNP additive reduced the penetration and RTFOT mass loss of pure bitumen; it increased the softening point, flash point, elastic recovery, and Marshall stability. According to the results of multiple response performance index (MRPI) optimizations performed at the selected parameters and levels with the 70/100 penetration bitumen used, the optimum levels were found to be 0.70% GNP rate, 145°C mixing temperature, 15 minutes mixing time, and 2000 rpm mixing speed. GNP provided energy saving and environmental advantages by reducing the optimum mixing temperature to 145°C. It also increased the permanent deformation resistance at high temperatures and cracking and fracture resistance at low temperatures by reducing the temperature sensitivity of bitumen.