The Virginia Department of Transportation (VDOT) specifies polymer-modified asphalt binders for certain asphalt mixtures used on high-volume, high-priority routes. These binders must meet performance grade (PG) requirements for a PG 76-22 binder in addition to elastic recovery requirements. This typically results in the use of binders containing styrene-butadiene-styrene (SBS) modifiers. However, other polymer modifiers may also be used to achieve the PG 76-22 classification. One of these modifiers is a copolymer of SBS and polyethylene (PE) (SBS-PE) another modifier is ground tire rubber (GTR). This study was undertaken to investigate the suitability of SBS PE modified PG 76-22 binder and GTR-modified PG 76-22 binder for use in Virginia. Each modified binder was used in a 12.5 mm nominal maximum aggregate size mixture to pave approximately 2.3 lane-miles. All mixtures were produced as warm mix asphalt using a foaming system. The binders evaluated included a typical SBS polymer-modified binder as a control and binders modified with SBS-PE and GTR. During construction, all processes were documented and material was sampled for evaluation. Binder and mixture tests were performed. Binder testing included performance grading and multiple stress creep and relaxation testing. Mixture testing included volumetric analysis, dynamic modulus, and flow number tests and cracking, rutting, and fatigue analysis. Binder testing indicated that the control binder and SBS PE modified binders met VDOT specifications for classification as a PG 76-22 binder; the GTR-modified binder graded to a PG 70-22 binder, as it did not meet the PG 76-22 high-temperature specification and did not pass the elastic recovery requirement. Laboratory mixture testing indicated that the performance of the SBS PE modified mixture should be similar to that of the control mixture. Laboratory test results for the GTR-modified mixture were mixed, with some indicating that the performance was similar to that of the control mixture and some indicating that the performance may be less than that of the control. Based on the study, SBS PE modified binders should continue to be allowed as an alternative to SBS-modified binder provided specifications for PG 76-22 binders are met. However, further investigation of GTR-modified binders is suggested before recommendations can be made. In addition, long-term evaluation of the field site is recommended for validation of the laboratory findings.

Polymer modified asphalts have recently been the focus of much attention in the U.S. due to claims that polymer additives will lengthen the life of an asphalt pavement. Much of the published research on this topic has been concentrated on the effects of polymer modifiers on binder and mixture properties. The goal of this testing is to predict from laboratory testing the actual field performance of an asphalt concrete. Over the years, specifications have been developed for conventional asphalts that allow pavement performance to be predicted from certain binder tests. These conventional binder tests do not fully address the special characteristics of polymer modified asphalt binders and need revision to be an effective tool in predicting pavement service life. This paper presents the findings of a two-part laboratory research program intended to relate binder and mixture properties of polymer modified asphalts. The preliminary testing involved five asphalt binder types and a variety of binder and mixture tests. Promising test procedures were further investigated in the final testing program where ten asphalt binders were examined. Simple linear regression was used to determine the strength of a relationship between pairs of binder properties and mixture properties. The preliminary testing showed penetration, toughness and tenacity, and force ductility to have the most promise in predicting mixture performance. The final testing contained enough data to be analyzed with both simple linear regression and multiple regression. Penetration, toughness and tenacity, force ductility again were the test procedures that had binder properties that correlated well with mixture properties.

Ohio Department of Transportation has adopted the hot mix asphalt concrete containing polymer modifiers for use in the interstate highway pavement. Among the various reasons cited for the adoption of polymer modifiers are the favorable field experiences by ODOT, extensive literatures reporting enhanced performance, such as rutting resistance, low temperature thermal cracking resistance, and possibly fatigue endurance. However, despite these favorable findings, there are still cases involving premature failure of hot mixtures containing polymer modifiers. Concerns regarding optimum polymer content, compatibility between polymer additives and asphalt cement, proper mixing and compaction procedure remain to be resolved. Furthermore, performance based specifications to ensure production of desirable final asphalt concrete product require additional development. Questions regarding the suitability of Superpave binder testing procedures for the polymer-modified binders need to be clarified.