Laboratory investigation on rheological, chemical and morphological evolution of high content polymer modified bitumen under long-term thermal oxidative aging

Abstract High content polymer modified bitumen (HCPMB) is now mostly used in porous asphalt pavement, and the developed polymer system causes it exhibit more complex characteristics than conventional bitumen. However, the research on the aging behavior of HCPMB is still very limited due to its high polymer content and severe aging degree. In this paper, four types of binders were selected for different time-course aging tests to simulate the aging of the actual pavement. Then, Dynamic Shear Rheometer (DSR), Fluorescence Microscopy (FM), Fourier Transform Infrared (FTIR) Spectroscopy, and Gel Permeation Chromatography (GPC) were conducted to track the rheological, chemical and morphological evolution of the four bitumens during aging. The multiple stress creep recovery (MSCR) test index can capture the decrease of elasticity due to polymer degradation, reflecting the better elastic sensitivity than rutting factor. The black diagram and master curve can better analyze the influence of polymer modification and aging on the viscoelastic properties, and polymer modified bitumen (PMB) showed obvious two-stage characteristics in the graph. The shear stress relaxation (SSR) test showed that aging could weaken the relaxation property of bitumen, which makes it easy to accumulate larger stress and lead to cracking. The micro-chemical test results more intuitively proved that the degradation of the polymer mainly occurs in the early stage of aging, and the oxidation of the bitumen phase is the dominant process of long-term aging. And the more developed the initial polymer network is, the slower the degradation rate of polymer is, thus prolonging the early stage of aging. Principal component analysis (PCA) showed that the complicated relationship between the 12 parameters analyzed in this study could be explained by SBS content and bitumen aging degree. This study can provide insights for exploring the macro and micro change characteristics of binders during the long-term aging process and better understanding the aging mechanism of HCPMB.