Multiple Stress Creep Recovery (MSCR) Testing Helps Predict Rutting
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Dynamic shear rheometry (DSR) methods have been refined recently, to better predict polymer-modified binder properties related to rutting and high temperatures. Current asphalt test standards now include AASHTO TP70, "Standard Method of Test for Multiple Stress Creep Recovery (MSCR) Test of Asphalt Binder Using a Dynamic Shear Rheometer (DSR)."
The MSCR test produces lab results that are closely correlated with actual mix performance. By dynamically loading the modified binder, and watching its accumulated "nonrecoverable creep compliance" (Jnr), the new test more accurate predicts polymer-modified binder performance, recognizing differences in polymer behavior at different temperatures and stress levels.
Using the MSCR test can often save money on polymer additives, by better matching the polymer level to needed performance. For an RET-modified binder, the test typically shows that very low levels of polymer can be used, to create binders that consistently outperform SBS and other modification methods.
"It is the Asphalt Institute’s opinion that MSCR represents a technical advancement over the current PG specification."
Bob Horan, P.E.