چكيده به لاتين
Although a small percentage of the asphalt mixture is composed of bitumen, the behavior of asphalt against environmental conditions, loading conditions is highly dependent on the behavior of bitumen. This is why the cause of many failures, problems and behaviors of asphalt pavements during their service life should be sought in the behavior and properties of bitumen. Bitumen is exposed to aging during the asphalt processing and paving service. During the aging process, the chemical properties of bitumen and the ratio of maltene to asphalt change. This change increases the viscosity and decreases the ductility as well as decreases the bitumen resistance to thermal cracking, which leads to a reduction in pavement durability. Various solutions and additives such as the use of recycling agents, soft bitumen, polymers, etc. have been proposed to restore the properties of aged bitumen.
In this research, 60/70 penetration grades of bitumen was used as a base bitumen. Aged bitumen was obtained by performing an aging simulation test (RTFO + PAV) on base bitumen. Recycling agents in three different categories of aromatic oils, Paraffinic oils and naphthenic oils were used to determine the suitable chemical composition to evaluate the feasibility of production of the bitumen recycling agent. In order to investigate the long-term effect of recycling agents on the properties of aged bitumen, the restored bitumens were tested in the aging simulator. Saturates, aromatics, resin and asphaltenes (SARA) fractionation, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), elemental analysis ,Penetration, softening point, rotational viscosity (RV), Multi Stress Creep and Recovery (MSCR) and linear amplitude sweep (LAS) were used to investigate different chemical, physical and rheological properties of bitumen sample.
Comparison of the performance of recycling agents indicates the different effects of these materials on the properties of bitumen. Recycling agents of aromatic oil, paraffin oil and naphthenic oil result in 42%, 42% and 38% reduction of the colloidal index of aged bitumen, respectively, which indicates the softening of aged bitumen and the stability of its colloidal structure. The results of the elemental analysis show a 42% increase in oxygen in aged bitumen after the addition of aromatic oil due to the unsaturated chemical structure of this oil. Paraffinic oil and aromatic oil increased the fatigue life of aged bitumen by 4.21 and 3.84 times, respectively, and increased it to a higher value than 60/70 penetration grades of bitumen. Naphthenic oil also increased the fatigue life of aged bitumen by 3.34 times and slightly less than 60/70 penetration grades of bitumen. Examination of long-term performance of restored bitumen showed that recycling agents improve long-term performance of aged bitumen. Paraffin oil has the best performance in restoring the chemical, physical and rheological properties of aged bitumen in the short and long term.
