Effect of ageing on micromechanical properties of bitumen by means of atomic force microscopy

This study focuses on morphological changes and micromechanical properties of bitumen and its components (maltenes and asphaltenes) under neat, laboratory short- and long-term, and long-term field ageing. The material was analysed by means of atomic force microscopy in pulsed force mode, allowing for material nano-mechanical measurements. It was concluded that the colloidal equilibrium of asphalt fractions is affected by a significant loss of low molecular weight components, and air oxidising the bitumen. In addition, stiffness and adhesion were measured for each condition. It was observed that the greatest contribution in stiffness is associated with polar components, while the adhesiveness is associated mainly with non-polar components. Finally, to relate the ageing process to chemical changes, Fourier transform infrared spectroscopy measurements were performed to quantify the functional groups associated with oxidation. Furthermore, thermodynamic analysis by means of differential scanning calorimetry was performed to explain some of the observed changes in micromechanical behaviour.