Performance grading of asphalt binders and pavement mixtures became a reality with the conclusion of the, “FHWA” 50 million dollar, Strategic Highway Research Program, “SHRP”, in March of 1993. “SHRP” developed new asphalt binder specifications and test criteria based on the engineering properties related to pavement performance. The new emphasis is on low temperature performance of aged binder materials.

Low temperature flexibility of aged asphalt binders became significant. Performance Grade “PG,” asphalt is based on the predicted temperature performance both high and low of asphalt binders. Neither Gilsonite nor post vulcanized crumb rubber have performed well under “SHRP” evaluations. “SHRP” specifications will cause increased demand for modified asphalt as state departments of transportation adopt the “PG” specifications.