60 th Annual Asphalt Contractors Workshop March 2, Rebecca McDaniel North Central Superpave Center

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1 60 th Annual Asphalt Contractors Workshop March 2, 2016 Rebecca McDaniel North Central Superpave Center

2 What is the MSCR test? Why was it developed? What do the numbers mean? What are the advantages/disadvantages? How to implement.

3 Cyclic loading and unloading test in DSR 1 second loading, 9 seconds relaxing (recovery) Two stress levels Low stress linear viscoelastic range High stress non-linear range Intended to better characterize modified binders Run at environmental/climatic temperature RTFO-aged binder Test method AASHTO T 350 Specification AASHTO M 332

4 Rutting test in Dynamic Shear Rheometer (DSR) Short-term aged (RTFO) binder Rutting parameter G*/sin d Characterizes binder stiffness, not elasticity One low stress level in linear range Rutting is not linear damage Low stress does not fully capture effects of polymers Many states added PG+ tests (elastic recovery, ductility, force ductility, phase angle limits, etc.) Need to test at higher stress in non-linear range to mobilize polymer-modified binders

5 DSR test run at frequency simulating free-flowing traffic. How to account for slow moving or very heavy traffic? That traffic increases chances for rutting. Solution was to increase binder stiffness to better resist rutting. Increasing temperature one grade (6 C) roughly doubles the binder stiffness. So, if climate calls for PG 58, use PG 64 for slow moving traffic, and PG 70 for very heavy traffic volumes. Leads to use of soft binders with high polymer contents. Expensive and stress sensitive.

6 Non-recoverable Creep Compliance (J nr ) Non-recoverable shear strain divided by applied shear stress J nr is related to resistance to rutting Percent Recovery at Different Stress Levels Difference between strain at end of recovery period and peak strain after creep loading Percent recovery is indicator of polymer in binder Percent Difference (J nrdiff ) is difference in J nr at different stress levels. J nrdiff = J nr3. 2 Jn r J nr0. 1

7 Use same equipment (DSR). May need software update. Blind to modification (original PG intent). In the sense that binders for a given area are treated the same. But also sensitive to presence of modifiers. Test at environmental temperature. No grade bumping. Helps avoid use of soft binders with high polymer contents. Faster, easier and more meaningful than PG+ tests. Straightforward accounting for traffic. Better characterizes resistance to rutting. Shown in many lab, accelerated and field testing programs.

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9 Need updated software or new DSR. Need to revise specs, pay items, grade designations, etc. MSCR may lead to lower polymer loadings. May or may not be a problem. Not necessarily grade equivalencies. PG 64S-22 probably = PG But does a PG 64H-22 = PG 70-22? Does a PG 64V-22 = PG 76-22? The old grade bumping (changing a grade) no longer valid. Need training.

10 Test RTFO-aged binder in MSCR at high environmental temperature, say 58ºC. Other PG tests remain the same. 25-mm DSR on Original binder at high environmental temp. 8-mm DSR on PAV aged binder at intermediate temp. S G*sinδ max 5000 kpa; H, V and E G*sinδ max 6000 kpa BBR at low environmental temp. Flash point and rotational viscosity as before. Add letter to indicate expected traffic level and/or speed. PG 58S-22, PG 58H-22, PG 58V-22, PG 58E-22.

11 Beginning January 1, 2016, all project designs will use AASHTO M 332 (MSCR) binder specification MnDOT Special Provisions for Specifications 3151 Bituminous Material and 2360 Plant Mixed Asphalt Pavement. Projects already let, or designed prior to January 1, 2016 and to be let, may still use binders specified in current MnDOT Standard Specifications for Construction, which use the AASHTO M 320 binder specification.

12 Understanding the MSCR Test and its Use in the PG Asphalt Binder Specification Two-hour free informational webinar ( Asphalt Institute Guidance Documents Implementation of the Multiple Stress Creep Recovery Test and Specification Using the MSCR Test with the AASHTO M320 Specification FHWA Technical Brief (FHWA HIF ) Contact me: Becky McDaniel, 765/ x226