Rheological property investigations for polymer and polyphosphoric acid modified asphalt binders at high temperatures

Polymer modified asphalt binders have been used with success in mitigating many major causes of asphalt pavement failures (e.g., permanent deformation, moisture induced damage, fatigue, etc.). The styrene butadiene styrene (SBS) is commonly used for producing PG 76-22 binder, but the market was hit with a shortage of butadiene back in late 2009, which affected both supply and cost of PG 76-22 throughout the entire United States. Therefore, some alternative modifiers such as elastomers, plastomers, recycled ground tire rubber, sulfur additives, and polyphosphoric acid (PPA) to substitute for SBS in PG 76-22 asphalt binders have been investigated for future applications in the industry. The objective of this study was to investigate the high temperature rheological properties of SBS and three alternative polymer modified binders with/without PPA. Two base asphalt binders (PG 64-22), four polymers, and one PPA were used to produce the modified binders. The tested rheological properties include rotational viscosity, fail temperature, G*/sin δ, phase angle, viscometry, amplitude sweep, frequency sweep, creep and creep recovery, and relaxation. The test results indicated that the PG 76-22 binders with two alternative polymers had noticeably lower viscosity values compared to SBS modified binders and thus need lower energy for mixing and compaction. In addition, for the binders used in this research work, the utilization of 0.5% PPA could reduce by 1.0% of additional polymer needed to produce the PG 76-22 binder. Moreover, the characteristics of viscometry, amplitude sweep, frequency sweep, creep and creep recovery, and relaxation spectrums of all modified binders were generally dependent upon polymer type, asphalt source, and test temperature.