Laboratory evaluation of the effects of long-term aging on high content polymer modified asphalt binder

Abstract

One of the most widely used polymer-based modifiers in asphalt binders is styrene–butadiene–styrene (SBS), which results in binders of increased modulus, strength, toughness, and resistance to permanent deformation. These properties are further improved with the increase of SBS polymer content in asphalt binders, producing binders such as high-content polymer-modified asphalt (HCPMA). Although the HCPMA binders commonly are used in porous asphalt pavements, limited research has been conducted on their aging performance. This paper used gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, and the dynamic shear rheometer (DSR) to explore the evolution of chemical and rheological properties of aging HCPMA binders. The study found that the aging of HCPMA is a combination of oxidation of the base asphalt binder and degradation of the SBS polymer, leading to modulus increase and phase angle decrease. The degradation of SBS happened mostly at the beginning and slowed after pressure-aging vessel (PAV) conditioning for 20 h, which resulted in the lowest rutting resistance of HCPMA binders. When SBS content was higher than 7.5%, more than half the SBS polymer remained after 80 h of PAV conditioning. Although the molecular weight of SBS decreased from 230,000 to 70,000 due to degradation, its modification effect was still significant. Moreover, high modification of SBS can retard the oxidation and hardening of base asphalt binder, especially after PAV conditioning for 20 h. Principal component analysis showed that 10 parameters used in this study could be explained by SBS content and asphalt binder aging extent. Based on PCA results, the complex modulus (G∗) and phase angle (δ) of HCPMA binders can be well fitted by the exponential function of SBS content and aging index.