The Multiple-Stress Creep-Recovery (MSCR) Test and Specification

R. Michael Anderson, Asphalt Institute John R. Bukowski, FHWA AASHTO Subcommittee on Materials Annual Meeting Burlington, VT August 1-5, 2011

Acknowledgments

• DTFH61-08-H-00030 – Cooperative Agreement between the FHWA

and the Asphalt Institute • John Bukowski, AOTR

• John A. D’Angelo • Asphalt Binder ETG • Member Companies of the Asphalt

Institute – Technical Advisory Committee

Discussion

• Background • Basics of the MSCR test • How do MSCR results (Jnr) relate to rutting? • How can MSCR Recovery be used and what

does it indicate? • How does the specification work? • Educational activities • Implementation activities

Fill-in-the-Blanks

“At the higher service temperatures, the ability of the asphalt binder, particularly modified binders, to resist plastic or non-recoverable shear deformation is critical to pavement performance related to rutting and shoving under load. The __________ test, currently in the early stages of development, applies a repeated shear stress to the test specimen and the accumulated, non-recoverable deformation is recorded. By measuring these non-recoverable shear strains, which are directly related to the shear strains produced by repetitive, dynamic traffic loadings, it will be possible to specify values of dynamic stiffness to regulate the permanent deformation characteristics of the asphalt binder.” ________________________________

Fill-in-the-Blanks

“At the higher service temperatures, the ability of the asphalt binder, particularly modified binders, to resist plastic or non-recoverable shear deformation is critical to pavement performance related to rutting and shoving under load. The indentation test, currently in the early stages of development, applies a repeated shear stress to the test specimen and the accumulated, non-recoverable deformation is recorded. By measuring these non-recoverable shear strains, which are directly related to the shear strains produced by repetitive, dynamic traffic loadings, it will be possible to specify values of dynamic stiffness to regulate the permanent deformation characteristics of the asphalt binder.” The SHRP Asphalt Research Program: 1990 Strategic Planning Document

DSR Operation: AASHTO T315

One cycle is complete...

Spindle Position

Time

C

A

A B C

A A

B

Effect of Phase Angle

0.90

0.92

0.94

0.96

0.98

1.00

60 65 70 75 80 85 90

Sin δ

Phase Angle, degrees

High Temperature Testing

• Repeated Shear Creep – Analogous to mixture test (RSCH) – Performed in DSR

• Controlled shear stress (i.e., 25 Pa or 300 Pa) • 100 cycles • 1-second load, 9-second rest per cycle • High test temperature (HT-?)

– Response: permanent shear strain (γp) or strain slope

Repeated Shear Creep

0

2

4

6

8

10

12

14

0 2 4 6 8 10

Time, seconds

Perm

. She

ar S

trai

n, %

Instantaneous shear strain Permanent

shear strain

Recoverable shear strain

Repeated Shear Creep

NCHRP 9-10: PG 82 Binders Repeated Shear Creep (70C, 300Pa)

0 2 4 6 8

10 12 14

0 2 4 6 8 10

Time, seconds

Perm

. She

ar S

trai

n, %

Repeated Shear Creep

NCHRP 9-10: PG 82 Binders Repeated Shear Creep (70C, 300Pa)

0 2 4 6 8

10 12 14

0 200 400 600 800 1000

Time, seconds

Perm

. She

ar S

trai

n, %

Ox

PE-s

SBS-r

Multiple Stress Creep Recovery Test

• Performed on RTFO-aged Binder • Test Temperature

– Environmental Temperature – Not Grade-Bumped

• 10 cycles per stress level – 1-second loading at specified shear stress

• 0.1 kPa • 3.2 kPa

– 9-second rest period

Multiple Stress Creep Recovery Test

• Calculate Non-recoverable Creep Compliance (Jnr) – Non-recoverable shear strain divided by

applied shear stress • “J” = “compliance” • “nr” = “non-recoverable”

• Calculate Recovery for each Cycle, Stress – Difference between strain at end of recovery

period and peak strain after creep loading

MSCR

0

2

4

6

8

10

12

14

0 2 4 6 8 10

Time, seconds

Perm

. She

ar S

trai

n, %

Instantaneous shear strain Non-recoverable (permanent)

shear strain

Recoverable shear strain

MSCR – Non-Recoverable Compliance (Jnr)

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30 35 40 Time, seconds

Stra

in, %

Cycle 1 Unrecovered (permanent) strain

Cycle 2 Unrecovered (permanent) strain

Cycle 3 Unrecovered (permanent) strain

Unrecovered Shear Strain Jnr = Applied Shear Stress

MSCR – Non-Recoverable Compliance (Jnr)

0

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0 5 10 15 20 25 30 35 40 Time, seconds

Stra

in

Cycle 1 Unrecovered (permanent) strain

Unrecovered Shear Strain Jnr = Applied Shear Stress

0.1 kPa Shear Stress

0.197 Jnr = 0.1 kPa = 1.97 kPa-1

0.197

Relationship between Jnr and ALF Rutting 25.6kPa

MSCR can adjust for field conditions and has excellent relations to performance.

Jnr = (4.74*Rut Depth) - 1.17 R2 = 0.82

0

0.5

1

1.5

2

2.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

ALF Rutting, in

Jnr

18

Mississippi I55: 6yr rutting Jnr 3.2 kPa

y = 0.2907x + 0.1297R2 = 0.7499

00.5

11.5

22.5

33.5

4

0 2 4 6 8 10 12

6 yr Jnr 3.2 kPabinder mod true grade rut mm 70C

Ultrapave SBR 70-27 4.5 1.7Styrelf SB 77-29 2 0.44

GTR 80 75-29 1.5 1.21Sealoflex SBS 82-27 3 0.19

Multigrade 72-24 5 2.13Cryo Rubber 75-28 7 1.62

Control 70-24 11 3.5

MSCR What is % Recovery?

• MSCR Jnr addresses the high temperature rutting for both neat and modified binders, but many highway agencies require polymers for cracking and durability.

• The MSCR % Recovery measurement can identify and quantify how the polymer is working in the binder.

y = 29.371x-0.2633

0

10

20

30

40

50

60

70

80

90

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1

Jnr kPa

% re

cove

ryMSCR % recovery can be added to validate polymer modification

High elasticity

Poor elasticity

Table for MSCR % Recovery minimum values

Minimum % Recovery for Measured Jnr values Jnr @ 3.2 kPa Minimum % Recovery

2.0 - 1.01 30% 1.0 - 0.51 35%

0.50 - 0.251 45% 0.25 - 0.125 50%

Validate Polymer Modification

y = 29.82x-0.39

R² = 0.54

2030405060708090

100110

0.00 0.10 0.20 0.30 0.40 0.50 0.60

Rec3

200

@ 6

4C, %

Jnr @ 64C, kPa-1

PG 76-22 Binders: MSCR3200

Recovery = 29.37*Jnr-0.26

Original DSR G*/sinδ Min 1.0

64

RTFOT 64 Standard MSCR3.2 <4.0

64

64 Heavy MSCR 3.2<2.0

64

64 Very heavy MSCR3.2 <1.0

64

PAV

S grade DSR G*sinδ Max 5000

28 25 22 19 16

H & V grade DSR G*sinδ Max 6000

28 25 22 19 16

Low temp BBR and DTT remain unchanged

[(MSCR3.2 – MSCR 0.1)/

MSCR 0.1] < .75

AASHTO MP19 (Proposed)

AASHTO MP19

• Grades – Based on Climatic Temperature

• High and Low Pavement Temperature – Traffic Designation

• “S” – Standard • “H” – Heavy • “V” – Very Heavy

AASHTO MP19

• PG 64-22V asphalt binder – What do I need to test? – What are the temperatures and criteria?

PG 64-22V Asphalt Binder

• Original (Unaged) Binder – COC Flash Point

• Must be ≥ 230°C – Rotational Viscosity @ 135°C

• Must be ≤ 3 Pa-s – DSR (AASHTO T315)

• G*/sin δ must be ≥ 1.00 kPa @ 64°C

PG 64-22V Asphalt Binder

• RTFO Aged Binder – RTFO Mass Change

• Must be ≤ 1.00% – DSR (AASHTO TP70)

• Jnr must be ≤ 1.0 kPa @ 64°C • Stress Sensitivity must be ≤ 0.75

PG 64-22V Asphalt Binder

• PAV Aged Binder – DSR (AASHTO T315)

• G*sin δ must be ≤ 6000 kPa @ 25°C – BBR (AASHTO T313)

• S(60) must be ≤ 300 MPa @ -12°C • m(60) must be ≥ 0.300 @ -12°C

Implementation

• Telephone survey in 2010 and since indicate that there are barriers to state MSCR implementation – Inadequate DSR equipment/software – Lack of resources to perform transitional tests – Lack of guidance from suppliers and other

states – Uncertainty about effect on binder supply and

modification

Implementation: SEAUPG

• Task Force agreed to conduct survey of 14 SEAUPG states – Determine current capabilities to run MSCR – Determine need for training – Find out what barriers exist to testing and/or

implementation • Completed survey from all 14 states were

received within two weeks

Survey Results - Barriers

• 9 of 14 states said biggest barrier was concerns over correlation between existing PG Plus and new MSCR criteria

• Comment: – Satisfied with the PG 76-22 polymer modified

binder performance. There is a perception that moving to MSCR test may result in lower polymer loading and reduction in binder performance.

Survey Results - Training

• 11 of 14 states said they could use some type of training – 8 requested classroom training – 9 requested laboratory training – Comments:

• More important than training is keeping abreast of progress around the country

• Internet based training would be preferred since travel is restricted

Why MSCR?

• Why Use the MSCR Test and Spec? – Non-recoverable creep compliance, Jnr, is

better correlated with pavement rutting than G*/sin δ

• The high temperature parameter is truer to the intent of the PG specification, that it be blind to method of modification

Why MSCR?

• Why Use the MSCR Test and Spec? – MSCR Recovery can be used to identify

elastomeric modification, thereby eliminating the need for many PG-Plus tests like Elastic Recovery

• Much quicker test • Not directly tied to performance

Asphalt Institute TAC

• Position of the Technical Advisory Committee of the Asphalt Institute. – “It is AI’s opinion that the MSCR test and

specification represent a technical advancement over the current performance-graded (PG) asphalt binder specification, AASHTO M320, which will allow for better characterization of the high temperature performance-related properties of an asphalt binder.”

Implementation Activities

• User-Producer Groups – Task Force participation – Coordination of round-robin testing

• Conducting testing for individual user agencies

Implementation Assistance

• Educational – FHWA Technical Brief

• FHWA‐HIF‐11‐038 – Asphalt Institute

• Guidance Document, “Implementation of the Multiple Stress Creep Recovery Test and Specification”

• Guidance Document, “Using the MSCR Test with the AASHTO M320 Specification”

• www.asphaltinstitute.org – Engineering/MSCR Information

Educational Activities

• MSCR Workshops – Understanding and Implementing the MSCR

Test and Specification – Rocky Mountain Asphalt User Producer

Group • March 2009

– Northeast Asphalt User Producer Group • September 2009 • Webcast, Recorded

– www.ct.gov/dot video on demand

Educational Activities

• MSCR Workshops – Understanding and Implementing the MSCR Test

and Specification – Background

• Why do we need a new high temperature parameter? – Justification

• How does the MSCR test meet the needs? – Basics

• How do the MSCR test and specification work? – Testing Considerations

• If it is important in T315 then it is important in TP70

Educational Activities

• Webinar – “Understanding the MSCR Test and its Use in the

PG Asphalt Binder Specification” • Two-hour informational webinar on the MSCR test and

how it is used in the specification – 31 August 2011

• 12:00 to 2:00 PM EDT – No cost, but registration required

• Limited to 100 registrants • www.asphaltinstitute.org/public/asphalt_academy/Webi

nars/MSCR_Test_and_its_Use.asp

More Information?

Contact: Mike Anderson Asphalt Institute 859-288-4984 manderson@asphaltinstitute.org

Thanks!