MSCR Implementation and Impacts on Asphalt Binder Grading

MAPA Contractors’ WorkshopMinneapolis, MN February 19, 2015

ByAndrew Hanz, Ph.D.Mathy Construction

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

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

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

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

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.

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.

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.

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).

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.

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

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”

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.

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.

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.

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

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.

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)

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.

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

Thank You

Andrew Hanz, Ph.D.Technical DirectorMTE Services608-779-6352(office)608-780-2509 (mobile)andrew.hanz@mteservices.com