Presentation on theme: "Regional Implementation of the MSCR Test"— Presentation transcript:
1 Regional Implementation of the MSCR Test Pennsylvania Asphalt Pavement Association54th Annual ConferenceHershey, PAJanuary 30, 2014Gregory A. Harder, P.E.
2 Past MSCR Presentations Development of Standard Practice for Superpave Plus Specifications - J. D'Angelo – 2005 – Burlington, VTBinder and Mixture ETG Update - J. D'Angelo – 2006 – Wilmington, DEFHWA Pavements Program - What's Happening - J. D'Angelo – 2007 – Mystic, CTCurrent Status for Multiple Stress Creep Recovery October 9, K. Mooney – 2008 – Atlantic City, NJAsphalt Mixture and Binder Expert Task Group Update - J. Bukowski – 2008 – Atlantic City, NJUpdate on National Issues - ETG Activity - J. Bukowski – 2009 – Portland, MEMSCR Test - A New High Temp Spec - J. D'Angelo – 2009 – Portland, MEUpdate on National Issues - ETG Activity - J. Bukowski – 2010 – Saratoga, NYBinder Grade Selection Using the MSCR Specification - J. D'Angelo – 2010 – Saratoga, NYUpdate on National Issues - ETG Activity - J. Bukowski – 2011 – Providence, RIRegional Implementation of the MSCR Test – G. Harder – 2012 – Philadelphia, PA
3 MSCR ImplementationThe use of polymer modified binders has grown tremendously over the past several yearsHowever, the most widely used binder specification in the U.S., AASHTO M 320, was based on a study of neat (unmodified) binders, and may not properly characterize polymer modified binders
4 Why doesn’t M 320 properly characterize polymer-modified binders? Current spec, G* and δ are measured in the linear visco-elastic range.For neat binders, flow is linear(strain increases in a constant proportion to stress) and therefore not sensitive to the stress level of the test.For polymer-modified binders, the response is not linear and very sensitive to the stress level of the test. The polymer chains can be rearranged substantially as the stress increases.The slide show continues with the second and third bullet items.Neat asphalts behave in a linear fashion, where the strain increases in a constant proportion to the stress.In polymer-modified binders, the strain does not always increase in a linear fashion. At higher stress levels, the polymer chains can be substantially rearranged, resulting in non-linear behavior.
5 PG Grading Alone Does Not Always Predict Performance Study of the two mixes with the same aggregate structure, but different binders.PG modified, no ruttingPG unmodified, 15mm rutFurthermore, PG grading alone does not predict performance, especially when comparing neat and modified binders.
6 Why Do We Need New Binder Test? PG BindersMost Common “Neat” Binder GradesPG 64-22PG 67-22Most Common “Modified” Binder GradePG 76-22Works OK for neat bindersDoesn’t work as well for modified bindersLike I said previously, the SEAUPG states decided to adopt the Performance Grade (PG) binder grading system back in the mid 1990s. Each of the states decided to adopt a series of binder grades for use in their states, depending on various factors.Probably the most common grades used in the SE are as follows:the most common “neat” or unmodified binders were PG and PGthe most common “modified” grade is PG 76-22Over the last 17 years, the PG system has served us pretty well. There is no doubt that we have come a long ways with this approach. So how does the specification working…click…the current PG grading system works well for the neat binders. However…click…experience and research has shown that the current PG does not work as well for modified binders. This was recognized from the start so many states decided to adopt additional tests (commonly referred to as “PG Plus” tests) like Elastic Recovery, phase angle or force ductility to ensure that the modifiers were present in the binder.
7 What happened as a result of M 320’s inability to fully characterize polymer-modified binders? Most states began requiring additional tests to the ones required in AASHTO M 320These mostly empirical tests are commonly referred to as “PG Plus” testsThese tests are not standard across the states – difficult for suppliersEven some of the tests that are the most common, e.g. Elastic Recovery, are not run the same way from state to state
8 States with a “PG Plus” Specification No PG Plus Spec
9 ER Information and Test Time The Elastic Recovery Test is an excellent tool to establish the presence of polymer modification.It takes about 4 hours to prepare and test samples for this information.However, it is a poor tool to evaluate the rutting performance of polymer-modified binders.The MSCR test can use the same sample already being run in the DSR to give more information in a few extra minutes.ER - Pour, cool, trim, load, pull, wait, measure
10 Multiple Stress Creep Recovery Test Performed on RTFO-aged BinderTest TemperatureEnvironmental TemperatureNot Grade-Bumped10 cycles per stress level1-second loading at specified shear stress0.1 kPa3.2 kPa9-second rest period
11 Multiple Stress Creep Recovery Test Calculate Recovery for each Cycle, StressDifference between strain at end of recovery period and peak strain after creep loadingCalculate Non-recoverable Creep Compliance (Jnr)Non-recoverable shear strain divided by applied shear stress“J” = “compliance”“nr” = “non-recoverable”
12 ALF Study - 7 Asphalt Binders AZCRM----70-22PG70-22ControlAirBlownSBSTXTBCRTPPG70-22+FibersPG70-22SBS64-40AirBlownSBSTPAn Accelerated Load Facility (ALF) at Turner-Fairbanks Highway Research Center conducted rut testing on mixes incorporating 7 different binder types. They then tried to correlate the binder performance as measured by Superpave binder testing and MSCR testing to the observed rutting.123456789101112
13 ALF Loading The pavement was heated to a constant 64ºC. The FHWA ALF uses an 18,000 lbs wheel load with no wheel wander.The speed is 12 MPH.This is a extreme loading condition far more sever than any actual highway.
14 Relationship between G*/ sinδ and ALF rutting As you know, the coefficient of determination, R2, is a measure of how well future outcomes can be predicted by a model, “0” being unable to reliably predict performance and “1” being a perfect predictor of performance. The Superpave binder grading, at an R2 of , is a poor predictor of modified binder rutting in this ALF study.Existing SHRP specification has poor relationship to rutting for modified systems.
15 Relationship between Jnr and ALF rutting 25.6kPa MSCR can adjust for field conditions and has excellent relations to performance.On the other hand, the MSCR Jnr, at an R2 of , is a reliable predictor of modified binder rutting in this ALF study.
19 AASHTO M320 Grades As an example, following Table 1… Kentucky’s climate requires a PG to meet high and low pavement design temperaturesPG is a standard, unmodified asphalt binder gradeFor Very Heavy (slow and/or very high volume) traffic, Kentucky “grade bumps” to a PG asphalt binderPG is a modified asphalt binder gradeKentucky requires ER ≥ 75%
20 AASHTO M320 Grades As an example, following Table 1… Although a PG is specified, Kentucky recognizes that the pavement temperature never gets that hotOriginal DSR (T315): G*/sin d ≥ °CRTFO DSR (T315): G*/sin d ≥ °CGrade bumping is a way to get a stiffer asphalt binder at the expected high pavement temperature
21 AASHTO MP-19 Grades As an example, following MP-19… Kentucky’s climate requires a PG to meet high and low pavement design temperaturesPG 64-22S is an unmodified asphalt binder grade that can be used for Standard (normal speed, normal volume) traffic conditionsFor Very Heavy (slow and/or very high volume) traffic, Kentucky requires a PG 64-22V asphalt binderPG 64-22V is a modified asphalt binder gradeParticularly if MSCR Recovery requirement is added
22 AASHTO MP-19 Grades As an example, following MP-19… Instead of increasing the test temperature as in M-320, Kentucky recognizes that the pavement temperature never gets that hot and adjusts criteriaOriginal DSR (T315): G*/sin d ≥ °CRTFO MSCR (TP70): Jnr ≤ °CGet a stiffer asphalt binder at the expected high pavement temperature
23 NEAUPG Tasked by steering committee Formed Implementation Team Mission statement, description, target audience, opportunities, obstacles, strategies, and goals identifiedPerformed round robin testingAll states participated in pooled fund, each will be obtaining/using the same Malvern DSRStates agreed to specify both MP 19 Jnr requirements and MP 70 MSCR Recovery requirements beginning January 2014(H, V, and E grades only – S grades remain M320)NY MP 19 on all grades including S, recovery H, V, and E grades only
26 MSCR % Recovery validates polymer modification AASHTO TP 70% Recovery above the line means asphalt binder is modified with an acceptable elastomeric polymerPlotting the % recovery can show the presence of an elastomeric polymer, as outlined in Appendix X2 of AASHTO TP 70.Below line - not modified with an elastomeric polymer26
27 MODIFIED GRADES IN THE NORTHEAST CURRENT GRADE – M320NEW GRADE – MP-19PG 76-22PG 64E-22PG 76-28PG 64E-28PG 70-28PG 64V-28PG 64-22PPG 64V-22PG 58-34PG 58H-34
29 MEDOTBASE – 58CCURRENT GRADE – M320NEW GRADE – MP-19PG 58-28PG 58S-28PG 58-34PG 58H-34PG 64-28(PPA)PG 58H-28PG 70-28PG 58V-28PG 76-28PG 58E-28Will be specifying for modified grades on Jan. 1, 2014 – PG 58V-28[PG 70-28] – little to no use of PG – not sure yet on PG (PPA modified)
30 NHDOTBASE – 58CCURRENT GRADE – M320NEW GRADE – MP-19PG 64-28PG 58H-28PG 64-28(PPA)PG 70-28PG 58V-28PG 76-28PG 58E-28Use a very limited amount of modified grades but will implement PG 58V and PG 58E grades on Jan. 1, 2014
31 NJDOTBASE – 64CCURRENT GRADE – M320NEW GRADE – MP-19PG 64-22PG 64S-22PG 76-22PG 64E-28Will be specifying MSCR for PG effective Jan.1, 2014 – not sure if it will be PG 64V-22 or PG 64E-22
32 Will implement on Jan. 1, 2014 if suppliers want to DelDOTBASE – 64CCURRENT GRADE – M320NEW GRADE – MP-19PG 58-28PG 58S-28PG 64-22PG 64S-22PG 70-22PG 64H-22PG 76-22PG 64E-22Will implement on Jan. 1, 2014 if suppliers want to
33 MDSHABASE – 64CCURRENT GRADE – M320NEW GRADE – MP-19PG 58-22PG 58S-22PG 58-28PG 58S-28PG 64-22PG 64S-22PG 64-28PG 64H-28PG 70-22PG 64H-22PG 76-22PG 64E-22Working on software upgrade to test for MSCR – will collect data for information – implementation of MSCR possible in 2014
34 VT-AOTBASE – 58CCURRENT GRADE – M320NEW GRADE – MP-19PG 52-34PG 52S-34PG 58-28PG 58S-28Currently running MSCR on 75% of the full set testing – base temperature will be 58C – but will test at 52C for those mixtures containing high RAP – all projects for 2014 have been bid – have been using MSCR on emulsion residue
35 CTDOTBASE – 58CCURRENT GRADE – M320NEW GRADE – MP-19PG 58-28PG 58S-28PG 64-22PG 64S-22PG 76-22PG 64E-22Limited amount of PG polymer modified is used - currently running test and collecting data – considering allowing substitution of MP-19 grades in 2014 with full implementation for all grades possible in 2015
36 Mass HighwayBASE – 58CCURRENT GRADE – M320NEW GRADE – MP-19PG 52-34PG 52S-34PG 64-28PG 64S-22 orPG 58H-28PG RubberPG 64?-28PG SBRCurrently discussing internally – want to talk with industry this winter as to how to move forward – no implementation on Jan.1 – hope to have better idea of direction in early 2014
37 NYSDOTBASE – 58/64CCURRENT GRADE – M320NEW GRADE – MP-19PG 58-34PG 58H-34PG 64-22PG 64S-22PG 64-22PPG 64V-22PG 70-22PG 64H-22PG 76-22PG 64E-22Full implementation MP-19 for all grades in 2014 – actual date yet to be determined