The effect of aromatic interactions on the elasticity of bituminous binders

In this paper, experimental support is provided showing the importance of polyaromaticity on the elastic properties of bituminous binders. Especially the size of the polyaromatic structures seems to play a crucial role. The observations indicate that larger conjugated aromatic structures provide stronger interactions and relate to the elastic behaviour at longer loading times or up to higher temperatures, while smaller aromatic structures determine more the elastic behaviour at short loading times or at low temperatures. In addition to aromatic interactions, natural wax can, upon crystallization, also induce increased elastic effects, especially at low frequencies. A large variety of binders was investigated: bitumen from straight distillation, visbreaking, solvent deasphalting and oxidation were included in the sample set. Average levels of aromaticity were determined by Fourier transform infrared (FT-IR) spectroscopy and by refractive index measurements. Chromatography combined with UV-visible absorption spectroscopy was used as an indicator of the average size of the aromatic structures. Rheological properties were determined using a dynamic shear rheometer, in a temperature range from 0 up to 90 °C. Good relations were observed between the phase angle measurements, at specific test conditions of frequency and temperature, and UV-vis absorption levels at specific wavelengths.