Comparison of the Performance of Shale Oil-Modified and Polymer-Modified Asphalts in Grand Teton National Park

ABSTRACT Pavement sections using two different asphalt binders were constructed on U.S. Highway 89 in Grand Teton National Park. The monitoring program associated with the polymer-modified and shale oil-modified asphalt pavements consisted of an evaluation of the performance of the pavements with respect to in-service aging and ride performance. The polymer-modified asphalt was a PG 70-22, and the shale oil-modified asphalt was a PG 64-22. At 98% design reliability, the performance grade that is recommended at this location is PG 58-40. Thus, the two asphalts did not satisfy the low-temperature (cracking) requirement but exceeded the high-temperature (rutting) requirement. It should be pointed out, however, that at the time of construction the Superpave® system was new and not in common use. The PG values and the 98% design reliability value were not finalized until 1998. The cause of fatigue cracking and raveling in the latter years of the project was considered to be, in part, the result of moisture damage. With respect to ride performance, the extent of rutting observed for the two different pavements after seven years of service was negligible. However, cracking was observed in both pavements after the second winter (1994–1995). The extent of transverse cracking was significantly less for the polymer-modified pavement than for the shale oil-modified pavement. Evaluation of the cracks seemed to indicate that they were either the reflection of original cracks or thermal cracks. It was demonstrated that the development of transverse (thermal) cracks was related to the number of times the pavement temperature went below the glass transition temperature of the binder.