BACKGROUND
Since the implementation of the Performance-Graded (PG) Asphalt Binder specification developed by the Strategic Highway Research Program (SHRP), the formulation and manufacture of asphalt binders used in pavements has changed considerably. Increased global demand for fuels and other petroleum-based products has led to the development of refining techniques that allow the extraction of increased amounts of higher value light products with lower sulfur contents from crude oil. A wider, more variable range of crude oil sources are being used to produce asphalt binders than was the case when the PG system was first developed. Additionally, materials such as polymers, polyphosphoric acid, re-refined engine oil bottoms (REOB), paraffinic base oils, rendered oils, bio binders, and ground tire rubber are increasingly being used to formulate and manufacture asphalt binders. Increased use of higher percentages of reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) is also driving the use of softer asphalt binder grades, which are often produced by adding various products to stiff binders. Although today’s asphalt binders typically continue to meet the requirements of the PG specification, highway agencies in the United States and Canada are increasingly experiencing premature failures of newly constructed pavements despite general compliance with existing pavement and mix design standards, construction methods, and materials specifications. These failures include distress typified by low- and intermediate-temperature cracking and raveling, aggregate loss, and instances of total surface course loss within 5 years. Concern is often expressed over embrittlement and a lack of adhesion and tackiness of the asphalt binders. Based upon changes in asphalt binder formulation and manufacture, current asphalt binder specifications, tests, and practices merit a comprehensive review to assure their effective contribution to satisfactory pavement performance. Research is needed to assess the existing PG binder specification, address the implications of these changes in formulation and manufacture on binder performance, provide tools to measure the performance-related characteristics of asphalt binders, and develop an updated specification that addresses current and future asphalt binders.
OBJECTIVE
The objective of this research is to propose changes to the current performance-graded asphalt binder specifications, tests, and practices to remedy gaps and shortcomings related to the premature loss of asphalt pavement durability in the form of cracking and raveling.
STATUS: Phase III in progress.
