Correlation between multiple stress creep recovery (MSCR) results and polymer modification of binder

Nationwide traffic loads are increasing, pushing conventional asphalt to its limit. Polymer modification of asphalt, which can improve both low and high temperature performance, is already available, however, in many cases traditional Superpave testing is not sensitive enough to quantify the impact of modification, dimensioning its use. elastic recovery and forced ductility, Superpave performance grade plus tests, are sensitive to polymer modification but are time intensive and costly. These obstacles have lead the New Jersey Department of Transportation to require styrene-butadiene or styrene-butadiene-styrene to be incorporated in all modified binder to ensure performance, causing supply shortages and rising cost in the state. A relatively new test developed by the Federal Highway Administration, Multiple Stress Creep Compliance (MSCR) offers a simpler procedure using the Dynamic Shear Rheometer (DSR), thus it does not require the expense of purchasing additional testing equipment. The objective of this study is to correlate MSCR test results to performance. Flow time testing was selected as the measure of performance for its high strain and destructive nature. After evaluating ten binders the results indicate flow time results improve as J_nr, the non-recoverable creep compliance decreases. J_nr is determined by dividing the non-recoverable (or permanent) shear strain by the applied shear stress. All samples recording a J_nr bellow 0.5 kPa^-1 performed well, while performance generally suffered as J_nr increased from there. The J_nr parameter is recommended to be used as a standard measure of performance for polymer modified binders with a 0.5 kPa^-1 or below criteria.