Effect of Aging on Physical, Chemical, and Thermal Properties of Bitumen
Syeda Aamara Asif, Naveed Ahmad, Syed Usman Asif, Syed Bilal Ahmed Zaidi, Saad Amin
Abstract
Bitumen is a complex hydrocarbon material that is used as a binder for the construction of road pavements. Asphalt pavements are frequently exposed to high temperatures that result in the aging of bitumen. This investigation reports the effect of aging on the chemical properties, mechanical properties, and thermal stability of bitumen. Pressure ageing vessel (PAV) was used to study the long-term aging of the bitumen. Characterization of binders was carried out using conventional testing, rheological measurements with a dynamic shear rheometer (DSR), and chemical study by SARA analysis, Fourier transform infrared spectroscopy (FTIR) analysis, and thermal stability analysis through thermogravimetric analysis (TGA) and dynamic scanning calorimeter (DSC) tests. Results presented that aging significantly affects the rheological, chemical, and thermal properties of bitumen. The aging of bitumen increased asphaltenes, resins, and decreased aromatics, saturates which increased the colloidal instability index (CII). A maximum increase in CII was observed after 20 h of PAV aging with a comparatively insignificant increase after 60 h of PAV aging. TGA results indicated that the unaged binder was most thermal sensitive, whereas 60 h PAV aged binder showed the least thermal sensitivity up to 550°C but lost maximum mass at 800°C. The endothermic DSC curve indicated that weight loss was due to evaporation up to 550°C, whereas a maximum mass loss at 800°C could be due to decomposition of asphaltene fraction as also verified from FTIR results. Aging increased the carbonyl index, and the rate of formation of carbonyl group was high for 20 h aged binder. Furthermore, strong increasing and decreasing correlations between different parameters of rheological, chemical, and thermal properties were observed.