By Mike Anderson, P.E.
This year, in the 34th Edition of the “Standard Specifications for Transportation Materials and Methods of Sampling and Testing,” the Multiple Stress Creep Recovery (MSCR) test and specification have left their “provisional” label behind and have become full standards.
The MSCR test – formerly AASHTO TP70 – has now become T350, “Standard Method of Test for Multiple Stress Creep Recovery (MSCR) Test of Asphalt Binder Using a Dynamic Shear Rheometer (DSR).” The associated PG specification – formerly MP19 – has now become M332, “Standard Specification for Performance-Graded Asphalt Binder Using Multiple Stress Creep Recovery (MSCR) Test.”
I thought about how these standards had come alive, which led me by free association to Peter Frampton’s classic live album “Frampton Comes Alive!” That led me to ponder the hit single off that album “Show Me the Way.” It occurred to me the song would be a great segue way to talking about MSCR implementation.
So I looked at the song lyrics and realized that I have no idea what he’s talking about. “And no one to relate to except the sea”? Huh? I guess I’ll just pass it off with a “You know, the 70s” accompanied by a knowing nod while wearing a T-shirt with the slogan “The Dude Abides.”
I can’t possibly connect that to MSCR implementation. But since I’ve already started…
It was just over eight years ago that I first wrote about the MSCR test in this feature. Since then there has been some refinement of both the procedure and specification. The Asphalt Institute and the Federal Highway Administration (FHWA) have partnered on a number of efforts designed to help users with the understanding and implementation of the MSCR test and associated specification.
For basic information on the test and its background, you can’t go wrong with the FHWA’s Tech Brief: FHWA-HIF-11-038, “The Multiple Stress Creep Recovery (MSCR) Procedure” (available at fhwa.dot.gov). For a good overview on implementation, I’d refer you to the Asphalt Institute Guidance Document, “Implementation of the Multiple Stress Creep Recovery Test and Specification” (available at asphaltinstitute.org).
Although both documents need a little updating – AI’s guidance document came out in 2010 – the basic foundation is, I think, solid. It is noted that several items need to be addressed in order to make an effective transition to the MSCR test and specification. Those are worth reviewing here:
1. Become familiar with the MSCR test
2. Become familiar with the specification
3. Conduct transitional testing as needed
4. Transition regionally and uniformly
5. Use MSCR Recovery if there is a need to identify elastomeric modification in an asphalt binder
6. …and, if using MSCR Recovery, eliminate the use of other PG Plus tests.
The first three items are pretty self-explanatory and specific to the user agency considering implementation. The user will need to first gain an understanding of the test and specification and perform some comparative tests to evaluate how they can make a transition to a new system.
The last three are also self-explanatory, offering general guidance to the asphalt industry as it progresses to implementation. It is important to recall that one of the goals of the original PG Binder Specification was to provide users with a performance-based specification for asphalt binders that would be blind to the method of modification and eliminate the proliferation of specifications specific to a particular user or product. AASHTO M332 comes closer to meeting that goal, but still needs uniform implementation by users on a regional and, ultimately, national level. The Asphalt Institute encourages members of the asphalt industry to work within their user-producer groups to make that transition uniformly A quick review of AI’s MSCR Implementation Database can help provide a glimpse at what users are doing in the implementation process.
In closing, remember that an artist can make a great album, but it is the listeners that propel it to a best seller and make it a classic.
For more information on the MSCR test and specification please visit the AI website or contact Mike Anderson (manderson@asphaltinstitute.org).
Mike Anderson is the Director of Research and Laboratory Services at the Asphalt Institute.