Quality verification of polymer-modified asphalt binder used in hot-mix asphalt pavement construction

In many regions and countries, highway agencies are interested in verifying the quality of asphalt binders placed on roads for quality assurance purpose. Particularly, as PG-graded, polymer modified asphalt (PMA) is increasingly used, the agencies are interested in examining if the specified PMA is fully used in the field or if the PMA has not been severely degraded after storage, handling, and plant production. This research investigated and compared various test methods for such purpose. Besides laboratory-prepared asphalt binder samples, actual pavements built with neat asphalt (pen 60/70), 30% of neat asphalt with 70% of PG76-16 PMA, 15% of neat asphalt with 85% of PMA, and 100% of PMA were used for study. The mixture production and construction processes were carefully planned and monitored to ensure that they are consistent with real construction operations. Test methods evaluated in this study include indirect tensile (IDT) strength and indirect tensile stiffness modulus (ITSM) of field cores, rheological parameters (G∗, δ, temperatures at which G∗/sinδ = 2.2 kPa) from dynamic shear rheological tests of binders, Gel Permeation Chromatography (GPC) and Fourier Transform Infrared Spectroscopy (FTIR). The study found that samples made of different proportions of PMA can be effectively differentiated by IDT strength, phase angle (δ), and FTIR spectrum. Even the FTIR spectra of extracted asphalt binders without being subject to strict binder extraction and evaporation procedure reveal useful information for quality assurance purpose. The study also further proved that RTFO-treated PMA samples cannot be used to establish quality criteria for field-extracted PMA binders because RTFO does not well simulate field aging of PMA.