Investigating binder aging during hot in-place recycling (HIR) of asphalt pavement

Hot in-place recycling (HIR) is considered as an effective way to reuse reclaimed asphalt pavement (RAP).Heating pavement is the core technology of HIR. To ensure construction workability, the pavement should be heated and held at a relatively high temperature. However, the high heating temperature of HIR may cause significant aging on the SBS modified asphalt, which is usually used in the pavement. The objective of this study is to understand the aging behavior of SBS modified asphalt in HIR and provide appropriate guidance for future HIR projects. In this research, eight kinds of asphalt binder samples were collected and extracted from different stages of a practical HIR project. They were then tested in terms of the chemical and rheological properties. The rheological properties of asphalt are evaluated by the frequency sweep testing and Multiple Stress Creep Recovery (MSCR) testing using the Dynamic Shear Rheometer (DSR). The chemical evolution during FTIR was tracked from Fourier Transform Infrared (FTIR) spectra and Gel Permeation Chromatography (GPC). The results of the experiments showed that the influence of long-term aging is quite significant and untreated pavement exhibits much lower elastic recovery due to the degradation of SBS polymer. HIR did cause some extent of extra aging to the treated pavement, Compared with Untreated, the Carbonyl index and molecular weight ratio of polymer of Heated (#3) are reduced by 34% and 39% respectively. The effect of heating gradient between different pavement depths is noticeable. The modulus of Surface is 2.69 times that of Bottom. The PB index of Surface is 0.37 times that of Bottom. There is no noticeable chemical reaction between the rejuvenator and the aged asphalt. After adding rejuvenator, the modulus of pavement decreased by 55%.