There is concern that the Superpave (an asphalt/aggregate mixture design and analysis system developed under the Strategic Highway Research Program [SHRP]) binder and mixture tests may not be suitable for use with various modified asphalt binder systems. SHRP research established test methods and specification limits for neat asphalt cement binders, as well as tests and prediction models for mixtures made using neat asphalt cements. These specification limits, prediction models, and test methods, including volumetric criteria, were established from limited correlation of field performance with laboratory-measured properties of neat binders and mixtures made using the neat binders.
A wide variety of modified asphalt binders are presently available. As a result, Superpave test methods may need to be altered to better characterize the modified asphalt binders and the hot-mix asphalt containing modified asphalt binders. Similarly, the specification limits, mixture performance tests, and models developed in SHRP research may also need modification as data on the field performance of modified asphalt binders and mixes containing modified asphalt binders become available. NCHRP Project 9-10 focused on these potential needs.
The objectives of this research were (1) to recommend modifications to the Superpave asphalt binder tests for modified asphalt binders and (2) to identify problems with the Superpave mixture performance tests in relation to mixtures made using modified asphalt binders.
The following items were transmitted to the TRB Binder Expert Task Group for review and possible future action by the AASHTO Highway Subcommittee on Materials: (1) a recommended practice, in AASHTO standard format, for advanced characterization of the performance properties of modified and unmodified asphalt binders; (2) methods for estimating practical laboratory mix and compaction temperatures of modified binders, their storage stability, and their particulate additive content; and (3) recommendations for changes to the present AASHTO specifications MP1 and MP1A and test methods TP1, TP3, and TP5.
The final report was published in August 2001 as NCHRP Report 459
. Copies of the modifier survey, the interim reports for Phases I and II, and the topical reports for Tasks 8, 9, and 10 are available for loan.