Impact of Anti-Stripping Agents on Performance Characteristics of Asphalt Binders and Bond Strength

Abstract: Anti-stripping agents (ASA) are blended with binders to increase moisture resistance and are essentially useful in locations prone to heavy rainfall or the availability of silica-rich aggregates. ASA are added to unmodified and modified binders, like crumb rubber modified binder (CRMB) and polymer modified binder (PMB). Though modified binders have improved moisture resistance, including ASA is necessary for runways and expressways in harsh environments.
Present practices use ASA of same chemical formulation for all types of binders without foreseeing consequences due to their interactions. Studies reveal that ASA alters binder rheology, leading to certain reduced performance characteristics. However, a systematic evaluation of binder interactions considering their variability in chemical formulations and intrinsic characteristics is lacking. Therefore, in the present research work, two classes of ASA (amine and silane) were blended with binders of different chemical formulations (unmodified-VG40, modified-PMB and CRMB). The methodology was designed to evaluate the interaction of amine and silane-based ASA in different phases; emphasizing the aging aspects and chemical alterations. Apart from the influence of ASA on basic binder characteristics, this study focuses on alterations in critical performance parameters such as cohesive, rutting, fatigue, and moisture resistance properties.
Binder characterization is assessed by performance-grade (PG) temperature and Bitumen-Typisierungs-Schnell-Verfahren (BTSV). Performance tests include force ductility (FD) for cohesion, multiple stress creep and recovery (MSCR) for rutting, binder yield energy test (BYET), linear amplitude sweep (LAS) for fatigue. Variation in chemical composition is evaluated using Fourier transform infrared spectroscopy (FTIR). Further, adhesion characteristics on aggregates of varying silica content; basalt, limestone, and sandstone were determined using binder bond strength (BBS) test.
Results indicated that PG is unaltered by the inclusion of ASA, while BTSV test reveals amine ASA reduces phase angle and failure temperature in VG40 indicating decreased stiffness and increased viscous properties. However, BTSV is unable to detect PMB modifications, likely due to 15kPa limit on complex modulus.
FD indicated a reduction in stiffness of binder and cohesion energy due to the addition of both ASA with CRMB and PMB, similar trend is observed with amine ASA and VG40. While rutting factor and MSCR parameters infer that amine ASA reduces the rutting resistance of VG40 and PMB, contrary results were obtained with CRMB. Fatigue performances evaluated using BYET and LAS provided similar results and indicated an alteration in binder properties due to the inclusion of ASA. However, BBS test revealed higher pull-off tensile strength and enhanced moisture resistance with ASA on all types of binders.
FTIR showed binder characteristics changes due to chemical modifications by ASA. Polymer degradation is observed in PMB by reduction in polybutadiene and polystyrene constituents that impart elasticity and stiffness. Remarkably, the inclusion of ASA with VG40 led to additional polymeric peaks at 911 and 690 cm-1 while no significant modifications were observed in CRMB.
The study concludes that the chemical interaction of ASA with binders may sacrifice some binder properties for better adhesion, with varying effects across binder types, thus necessitating a thorough evaluation before selection.
Keywords: Anti-stripping agent, modified binders, rheology