Development of a Long-Term Durability Specification for Modified Asphalt (0-4688-S)

This project summary report summarizes the research performed in Texas Department of Transportation (TxDOT) Project 0-4688. This two-year project was designed to develop (1) a better quantitative understanding of the relation between laboratory accelerated binder aging and field aging, (2) a test procedure to measure properties of an aged binder that relate to failure on the road, and (3) a proposed specification for estimating the relative durability of binders in the presence of oxidative aging. Tests were conducted on original base and polymer-modified binders, laboratory compacted mixtures, and pavement-aged binders. The project necessarily evolved to a more comprehensive approach to improving pavement service life. Methods for significantly improving pavement durability should be implemented: (1) construct pavements with the lowest possible accessible (interconnected) air voids, consistent with other best construction and mix design practices; (2) use mix designs that have an inherently low decrease in fatigue life with binder oxidation, coupled with an appropriately high initial fatigue life; (3) use binders with a minimum stiffness at the PAV* 16 hour condition (consistent with the appropriate performance grade); (4) use the pavement aging model for pavement design; (5) use binders that have inherently slow hardening rate kinetics; and (6) use modifiers that provide the most reduction in the hardening rate. Items 1 and 2 have a dramatic impact on pavement service life but require additional research for the most effective implementation: (1) determine the parameters that govern the decline of mixture fatigue life with binder hardening; and (2) determine methods to reliably, and with minimal risk to other construction parameters, achieve very low accessible air voids in pavements.