Comparison of long-term influence of various recycling agents on bitumen rheological properties

Bitumen rejuvenators are increasingly being used to restore aged bitumen and improve its long-term performance in pavement construction projects. The purpose of this research is to examine the effect of different recycling agents (naphthenic oil, paraffinic oil, and aromatic extract) on restoring aged bitumen and improving its long-term performance. The optimal percentage of each agent was determined by penetration and softening point tests and then added to aged bitumen to obtain restored bitumen samples. The restored bitumen samples were then aged again with RTFO and PAV tests, and compared with aged and virgin bitumen samples using various chemical, physical and rheological tests. The long-term performance of the samples was examined through various tests, such as Fourier transform infrared spectroscopy (FTIR), penetration, softening point, rotational viscosity (RV), linear amplitude sweep and multiple stress creep recovery (MSCR) tests. The FTIR test showed that recycling agents reduced the sulfoxide and carbonyl indexes of aged bitumen. The findings indicated that compared to naphthenic oil, paraffinic and aromatic oils had a higher penetration index value, thereby decreasing the temperature sensitivity of bitumen. Adding naphthenic oil, paraffinic oil, and aromatic extract to aged bitumen resulted in a decrease in the RV value by 54%, 52%, and 46%, respectively. Comparing the fatigue life of bitumen samples at a 5% strain level showed that aromatic extract and paraffinic oil increased the fatigue life of aged bitumen by 4.21 and 3.84 times, respectively. In the MSCR test, among the samples, the restored bitumen by paraffinic oil indicates better resistance to rutting. Also, the statistical analysis showed that mixture and temperature will have a significant effect on the characteristics of rutting relative to other parameters. The utilization of recycling agents improved the restored bitumen performance similar to virgin bitumen, with paraffinic oil showing the best long-term performance.