Influence of SBS Modifier on Aging Behaviors of SBS-Modified Asphalt

Aging behaviors of styrene-butadiene-styrene copolymer (SBS)-modified asphalt are complex due to combined effects of hardening of asphalt matrix and degradation of SBS. In order to investigate aging mechanism of SBS-modified asphalt more clearly, a novel method to extract SBS modifier from SBS-modified asphalt was introduced in this paper. Aging methods adopted in this study included thin film oven test (TFOT), pressure aging vessel (PAV), and ultraviolet light (UV) aging. After different aging methods, the physical and rheological characteristics of SBS-modified asphalt were evaluated. Chemical structures and molecular weight of extracted SBS modifier and SBS-modified asphalt were analyzed by Fourier-transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) tests. The results illustrated that aging led to the degradation of the SBS structures, which could influence the physical and rheological properties of asphalt significantly. According to FTIR and GPC analyses, PAV aging had the obvious influence on the oxidation, fracture, or crosslinking of polybutadiene chain segment, and UV aging had the most obvious effect on degradation of large modifier molecules. Based on this extraction method, the peaks for butadiene structure in FTIR spectrum and the peaks of SBS molecular weight in GPC became increasingly apparent, and changes of those peaks before and after aging were clearer than that based on SBS-modified asphalt. All the previous results indicated that the new extraction method was useful for investigating the aging behaviors of SBS modifier without the influence of base asphalt. Furthermore, methyl index (MI) could be utilized to investigate the aging of SBS modifier based on this new extraction method. Pearson correlation coefficient result showed that the new extraction method was more suitable to characterize the close relationship between the aging of SBS modifier and the changes of asphalt rheological properties after aging.