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MSCR Implementation and Impacts on Asphalt Binder Grading
MAPA Contractors’ WorkshopMinneapolis, MN February 19, 2015
ByAndrew Hanz, Ph.D.Mathy Construction
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Overview of MSCR Implementation
• Details of the Test Procedure– What is the test temperature?
– What is the test measuring?
– How is it different than what we do today?
• Combined States Binder Group (CSBG) Implementation– Staged Approach
– What to expect
– Impact to current products
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MSCR AASHTO Standards
• T350: Standard Method of Test for Multiple Stress Creep and Recovery (MSCR) Test of Asphalt Binder using a Dynamic Shear Rheometer.
• M332: Standard Specification for Performance-Graded Asphalt Binder Using Multiple Stress Creep Recovery (MSCR) Test
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Multiple Stress Creep and Recovery Test (MSCR) – AASHTO T350
• 10 cycles at 2 stress levels (0.1 kPa and 3.2 kPa. 1s loading followed by 9s unloading.
• Run at climatic high temperature (i.e. 52C or 58C).
• Intended to apply to modified and unmodified binders.
Rutting Resistance (Jnr)
http://www.fhwa.dot.gov/pavement/materials/pubs/hif11038/tb00.cfm
Polymer Presence (%R)
unrecovered strain after 10 cycles
Applied Stress
γRecovered Strain
γPeak Strain
Non-recoverable compliance
% Recovery
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0 25.000 50.000 75.000 100.000 125.000 150.000 175.000 200.000 225.000
time global (s)
0
20.000
40.000
60.000
80.000
100.00
120.00
st
ra
in
1344, AAA-R, MRL MSCR RR, 58°, AR-3-0001c-2 1344, AAA-R, MRL MSCR RR, 58°, AR-3-0001c-2, Creep - repeat 1
Data Generated During Test
0 25.000 50.000 75.000 100.000 125.000 150.000 175.000 200.000 225.000
time global (s)
0
1.0000
2.0000
3.0000
4.0000
5.0000
6.0000
7.0000
8.0000
st
ra
in
MIA 70-28, Tk 37, 09-30-2013 (11-21-13-C), 05-08-14-C, RTFO, 58° MSCR, AR-2-0001cMIA 70-28, Tk 37, 09-30-2013 (11-21-13-C), 05-08-14-C, RTFO, 58° MSCR, AR-2-0001c-2, Creep - repeat 1
00
4.0
100
8.0
200
Stra
in
Time 120St
rain
60
00 100 200
0.1 kPa 3.2 kPa
0.1 kPa 3.2 kPa
PG 70-28P @ 58°C
PG 58-28 @ 58°C
• Presence of polymer is clear in response during rest periods.
• PG 70-28: significant recovery of accumulated strain during rest period.
• PG 58-28: Strain vs. time curve is flat during rest period = no recovery.
• Test can rank the rutting resistance of modified and unmodified binder.
• Accumulated strain of 120 (PG 58-28) vs. 8 (PG 70-28).
• Parameter accounts for both creep and recovery response.
%Recovery
Jnr
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Test at the Climatic High Temperature Grade
LTTPBind• Database that provides
pavement temperatures needed for PG selection.
• Includes levels of 50% and 98% reliability.
46°C
52°C
58°C
64°C
Graph shows 98% reliability
temperatures.
Majority of MN has high pavement PG temperatures of 52°C or 58°C.
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Current Asphalt Binder Specifications
• Performance Grade (PG) – AASHTO M320– Rating system for selection of asphalt binders with
material properties appropriate for climate.
– Applies to both conventional (PG 58-28, PG 52-34, etc.) and modified grades (PG 58-34P, PG 64-34P…).
• PG Plus Specifications– Additional tests that ensure that polymer is present.
Tests include elastic recovery, MSCR, etc.
– Called out in specifications using “P” grade. For example a PG 58-34 and PG 58-34P would have different testing requirements.
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New Asphalt Binder Specifications• Apply same testing framework to all binders.
• Performance Grade (AASHTO M332)
• PG Plus Specifications– MSCR %R as an indicator of polymer presence and performance
impacts. No additional tests needed.
Original Binder
G*/sinδ>1.0 kPa LTTPBind High Temp. Same as current system (M320)
RTFO Aged Binder
MSCR Jnr requirements
LTTPBind High Temp. AASHTO M332
PAV Aged Binder
G*sinδ<5000 kPa Intermediate Temp.Same as current system (M320)
BBR LTTP Bind Low Temp.
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CSBG Implementation of MSCR – 2 Phases
• 2015: Replace current “PG Plus” tests with MSCR %Recovery– Applies only to binders that are called out as
polymer modified “P” in bid documents.
• 2016: Full Adoption of AASHTO M332 as a PG Grading Test – Grade based on climate only (no grade bumping).
– Followed by a letter to designate traffic rating (S, H, V, E).
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MSCR Implementation Phase I
Replace “PG Plus” Specifications with MSCR % Recovery. For MN these include: Elastic Recovery (AASHTO T301) and Phase angle.
Advantages• Time: AASHTO T301 takes approximately 3hrs, MSCR < 30 mins.• Precision: Remove subjectivity from measurements in AASHTO
T301 by using DSR.
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How were MSCR %R Limits Set?Example: Tests at 58°C
0
10
20
30
40
50
60
70
80
90
100
0 0.5 1 1.5 2
% R
eco
very
Jnr 3.2 kPa
M332
58-34
64-28
64-34
70-22
70-28
70-34
76-28
82-22FAILING
Min %R
30%
55%
75%
• Jnr and %R are related (black line). AASHTO M322 proposed limit. Above the line is passing.
• Limits were set based on test results on materials from state DOTs and suppliers.
PASSING
*Figure adapted from CSBG
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2015 MSCR Implementation Phase I
AASHTO M320Grade
Test Temperature
58°C 64°C
52-34 0 058-28 0 064-22 0 0
58-34P 30 2564-28P 30 2564-34P 55 4570-22P 55 4570-28P 55 4570-34P 75 7576-28P 75 7576-34P 75 7582-22P 75 75
2015 CSBG: MSCR %R Limits
• Related MnDOT Bid Items (2360) PLANT MIXED ASPHALT
PAVEMENT – POLYMER MODIFIED BINDER
(3151) BITUMINOUS MATERIAL –POLYMER MODIFIED BINDER
• Statement of Estimated Quantities – Designer Note
“Plant Mixed Asphalt Pavement –Polymer Modified Binder (PMB) will need to meet the Percent Recovery requirements indicated in Table 3131.2A of the Special Provision”
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Implementation Phase ICurrent Products vs. Proposed Limits
• Asphalt binders produced for past construction seasons were tested to develop MSCR %R limits.
• Tests @ 58°: Most limits were based on 100-300 tests. Outliers are PG 70 grades (PG 70-22, 70-34, 76-28, PG 76-34)
>90% of samples passed %R for most grades.
80% of samples passed %R for PG 64-28.
• Tests @ 64°C: Limits were based on fewer tests.
– PG 64-28 and PG 64-34: ~85% of samples passed %R (~80 total tests)
– All other grades: Testing frequencies were low (<20) and results varied.
• Recommendations – Due to small sample size:
Check specialty grades (76-34, 76-28, PG 70-22, etc.)
Verify tests at 64°C meet requirements.
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2016 MSCR Implementation Phase II Full Adoption of AASHTO M332
• Review AASHTO M320.
• Introduce concepts of the M332 grading system and how it is different.
• Provide examples on M320 and M332 grade equivalents.
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What we do nowAASHTO M320 Binder Grade Selection
PG 58-28Traffic
Volume
ESALs
Traffic Speed
Standing Slow Standard
<0.3 (~ +1) - -
0.3 to < 3 +2 +1 -
3 to <10 +2 +1 -
10 to < 30 +2 +1 (~ +1)
> 30 +2 +1 +1
+1 : Increase PG grade by 6 degrees; e.g. PG 64-22 to PG 70-22
LTTP Bind Data:
58: Avg. 7 day max
pavement design temp.
-28: Min. pavement
design temp.
CLIMATETRAFFIC CORRECTION (aka Grade Bumping)
• Example: PG 58-28 for E3 and Slow Traffic = PG 64-28. This means the binder must meet AASHTO M320 requirements at 64°C.
• Climate does not change – grade bump is an empirical way to account for loading conditions.
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AASHTO M332 Grading System
Example: PG 58V-34• 58: Avg. 7 day max pavement design temp.• V: Traffic rating• -34: Min. pavement design temp.
Traffic Rating
MaximumJnr (kPa-1)*
Traffic Guidelines (ESALS and Traffic)
SStandard
4.5<10 mil ESALs and standardtraffic loading
HHeavy
2.010-30 mil ESALs or slow moving traffic.
VVery Heavy
1.0>30 mil ESALs or standing traffic.
EExtreme
0.5>30 mil ESALs and standing traffic.
Test temperature remains the same for all traffic ratings.
*Final limits TBD by CSBG
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AASHTO M320 (PG) vs. AASHTO M332 (MSCR)Similarities
– Starting point based on 7 day high pavement temperature.
– Used to control binder resistance to permanent deformation.
Factor M320 HT DSR M332 MSCR Test
Mode of loading Oscillation Creep and Recovery
Polymer Identifier Phase Angle %Recovery
Traffic Adjustment Grade Bumping: Maintainspecification limit, change test
temperature.
Performance Based: Maintain test temperature, change specification limit
Differences
Performance based methodology of MSCR is an improvement because material is tested at a temperature that represents the project climate for all loading conditions.
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AASHTO M332 Grading SystemAASHTO M320 Grade Equivalents
• S grade is equivalent to unmodified binders.• H, V, and E grades represent different levels of
modification and will have to meet both Jnr and %R limits.
S (Standard): Jnr ≤ 4.5 kPa-1
H (Heavy): Jnr ≤ 2.0 kPa-1
V (Very Heavy): Jnr ≤ 1.0 kPa-1
E (Extreme): Jnr ≤ 0.5 kPa-1
Grade (AASHT0 M332)
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Summary and Guidelines1. 2015 (Stage 1): Using MSCR %R for Modified Binders:
Products with a “P” designation or project documents that refer to “Polymer Modified Binder” require the MSCR test.– For “common” grades most binders will meet limits.
>90% of CSBG samples tested passed.– Re-test “specialty grades”. Small sample size used by
CSBG
2. 2016 (Stage 2): Full Adoption of AASHTO M332: Grade will look different than in the past and include an “S, H, V, or E.”– S grades will need to meet Jnr only. H, V, E grades will
need to meet %R and Jnr.– Get spec. requirements from agency and verify that they
are met. May need to re-formulate binder.
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Additional Resources
• Federal Highway Administration– Tech Brief:
http://www.fhwa.dot.gov/pavement/materials/pubs/hif11038/hif11038.pdf
• Asphalt Institute – Information Page: http://www.asphaltinstitute.org/mscr-information/
– MSCR State Implementation Database: http://www.asphaltinstitute.org/specification-database/state-mscr-implementation-status-database/
• Combined State Binder Group– https://engineering.purdue.edu/~ncaupg/Activities/Combined%20Stat
e%20Binder%20Group.html
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Thank You
Andrew Hanz, Ph.D.Technical DirectorMTE Services608-779-6352(office)608-780-2509 (mobile)[email protected]