The National Academies

NCHRP 20-44(25) [Completed]

Workshop to Introduce Proposed Changes to AASHTO M 320 and M 332 to Key Stakeholder Groups
[ NCHRP 20-44 (NCHRP Implementation Support Program) ]

  Project Data
Funds: $50,000
Research Agency: D'Angelo Consulting, Inc.
Principal Investigator: John D'Angelo
Effective Date: 2/1/2020
Completion Date: 10/15/2020


Since the implementation of the Performance-Graded (PG) Asphalt Binder specification in the 1990s, 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.

Today’s asphalt binders typically continue to meet the requirements of the current PG specifications (AASHTO M 320 and M 332), but highway agencies in the United States and Canada have increasingly experienced 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.

NCHRP Project 09-60 assessed the existing PG binder specifications, evaluated the implications of these changes in formulation and manufacture on binder performance, and developed proposed changes to AASHTO M 320 and M 332 to better characterize the cracking potential of unmodified and modified asphalt binders. These changes would introduce new binder rheological and cracking measurements to the present specifications.


The objective of this implementation activity was to conduct a facilitated 1- or 1½-day workshop to (a) introduce the tentative changes to the AASHTO M 320 and M 332 performance graded asphalt binder specifications developed in NCHRP Project 09-60, (b) identify their potential benefits and costs, impediments to their adoption, and potential impacts on public and private stakeholders, and (c) identify necessary actions to expedite their validation and adoption.


The deliverables was provided to the AASHTO COMP and the NCHRP Project 09-60 panel.

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