Evaluation of Current Modified Asphalt Binders Using the

Multiple Stress Creep Recovery Test

Carl Thodesen, Szabolcs Biro, & John Kay

Introduction

• Idea for research started following work done by Association of Modified Asphalt Producers (AMAP)

• Research entitled: Polymer Asphalt Supply Outlook

• Conduct market research on availability of polymers for use in asphalt modification

Why is SBS Currently in ShortSupply?*

• Styrene-Butadiene-Styrene (SBS) polymer capacity is not short

• Shortage of raw materials

• Ethylene production is the problem

*Slide courtesy of R. Corun: “Asphalt & Polymer Supply Outlook”, NEAUPG Meeting, Atlantic City, NJ October 8, 2008

Why is Ethylene Production the Problem?*

• By-products of Ethylene Production:– Styrene– Propylene– Butadiene– Isoprene– Pentadiene– Cyclopentadienes– Aromatic Resin Formers– Isobutylene– Amylenes– Hydrogen– Benzene

Ethylene

*Slide courtesy of R. Corun: “Asphalt & Polymer Supply Outlook”, NEAUPG Meeting, Atlantic City, NJ October 8, 2008

Ethylene and Butadiene Market Comparison*

• Ethylene Market– 120 million tons per

year– Primary use:

Packaging materials• Plastic wrap• Trash bags• Milk jugs

• Butadiene Market– 14 million tons per

year– Primary use: Tires

(70%)– Multiple other

automotive and durable good uses

– SBS polymer for asphalt (6%)

*Slide courtesy of R. Corun: “Asphalt & Polymer Supply Outlook”, NEAUPG Meeting, Atlantic City, NJ October 8, 2008

Ethylene Production

Issues

• Not possible to use non modified asphalt in lieu of modified asphalt

• Using the wrong grade will lead to poor performance

• Data exists to confirm that modified asphalt improves pavement performance

• Flexibility and creativity necessary to find answers

AMAP Recommendations

• AMAP concludes:– “prudent planners should be working on the

basis that availability of SBS polymers will remain tight for the immediate future. “

– Alternatives should be investigated:• Reacted Ethylene Terpolymer (Elvaloy)• Ethyl Vinyl Acetate (EVA)• Ground tire rubber (GTR)• Hybrid Binders (SBS-GTR)• Polyphosphoric acid (PPA)

Common Modification Agents*

SBS M

odified

SB M

odified

SBR La

tex M

odified

Other Polym

er Modified

(EVA, e

tc)

Chemica

l Modified

(oils,

etc)

Other (G

TR)

PPA

Other Chem

ical (A

ir Blown)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%80%

45% 45%

19%12%

16% 16%13%

85%

56%53%

15%12%

18%21%

12%

2005 2006

*AMAP , 2006

Research Scope

• Evaluate all AMAP recommended modified binders using MSCR.

• Provide data identifying strengths and weaknesses of various modified binders.

• Identify modifier best suited to use in place of SBS from performance data.

Binders TestedModified Asphalt Additive Used

Concentration (% by weight of total blend)

SBS Calprene 501C 3

Asphalt rubber Ambient crumb rubber 20

SBS-CRM Calprene 501C 1

Ambient crumb rubber 10

EVA EVATENE 3325 6

Elvaloy Elvaloy 4170 1

SBS-PPA Calprene 501C 2

Polyphosphoric acid 0.2

Note: Modifier percentages based on manufacturer recommendation

MSCR (ASTM D7405-08)

• Test developed as procedure for discriminating between modified binders– Performed using DSR on RTFO aged samples

• Possible alternative to PG Grading• Percent recovery and non-recoverable

creep compliance by means of MSCR test determined

MSCR Test Protocol

• Test run at selected temperature (64,70, & 76oC) using constant stress creep of 1.0 second duration followed by a zero stress recovery of 9.0 second duration.

• Test run at two stress levels: 100 Pa and 3200 Pa

• Ten cycles run at each of the two stress levels for a total of 20 cycles.

MSCR: Percent Recovery• Purpose: determine presence of elastic

response and stress dependence of modified and unmodified asphalt binders.

MSCR: Non-Recoverable Creep Compliance (Jnr)

• Non-recoverable creep compliance provides indication of stress dependence of the binder.

Complete loading cycle at 70oC

0 200 400 600 800 1000 12000.1

1.0

10.0

100.0

1000.0

10000.0

AR Elvaloy EVA SBS-CRM SBS-PPA SBS

Time (s)

Stra

in (%

)

Discussion Points

• AR tended to achieve the best results as it consistently yielded the lowest strain values

• SBS, AR, and SBS-CRM:– Less susceptible to the higher stress level– Demonstrate higher capacity to withstand

stress without deforming

First cycle at 70oC and 100 Pa

0 10 20 30 40 50 60 700

2

4

6

8

10

12

14

16

18

20

AR Elvaloy EVA SBS-CRM SBS-PPA SBS

Time (s)

Stra

in (%

)

Percent recovery at 100 and 3200 Pa at 70oC

100 32000

20

40

60

80

100

120

140

160

180

AR Elvaloy EVA SBS-CRM SBS-PPA SBS

Shear Stress (Pa)

Reco

very

(%)

Discussion Points

• AR samples exhibited the highest percent recovery, regardless of stress level.

• SBS-CRM binder yielded high percent recoveries, however, it was seen that at the higher loading rate the SBS-CRM blend did not recover as much as the SBS and asphalt rubber

Percent Recovery versus Temperature

58 64 70 76 820

20

40

60

80

100

120

140

160

180

R² = 0.948710530023546

R² = 0.999329836745937

R² = 0.954210991885703

R² = 0.952131591440598R² = 0.996877366014461

R² = 0.604111959565446

AR Linear (AR) Elvaloy Linear (Elvaloy) EVA Linear (EVA)SBS-CRM Linear (SBS-CRM) SBS-PPA Linear (SBS-PPA) SBS Linear (SBS)Linear (SBS)

Temperature (oC)

Reco

very

(%)

Discussion Points

• Linear relationship between the percent recoveries (64 – 76oC)

• SBS and the SBS-CRM blends are the least temperature sensitive

• AR Yielded highest values

Difference in Recovery

58 64 70 76 82-20

0

20

40

60

80

100

120

R² = 0.265018160217717

R² = 0.995892783383295

R² = 0.99607157576166

R² = 0.999878560813297

R² = 0.998116263330757

R² = 0.226242860034229

AR Linear (AR) Elvaloy Linear (Elvaloy) EVA Linear (EVA) SBS-CRM Linear (SBS-CRM)SBS-PPA Linear (SBS-PPA) SBS Linear (SBS)

Temperature (oC)

Rdiff

(%)

Discussion Points

• SBS: least difference in recovery between 100 and 3200 Pa

• EVA and Elvaloy: greatest differences in difference of recovery

• AR and SBS modified binder are less sensitive to differences in temperature and loading

Jnr Values for 3200 Pa

64 70 760.00

0.10

0.20

0.30

0.40

0.50

0.60

0.05

0.13

0.33

0.04

0.18

0.44

0.00 0.010.03

0.07

0.18

0.40

0.00 0.00 0.000.00 0.00

AR Elvaloy EVA SBS-CRM SBS-PPA SBS

Temperature (oC)

Jnr

0.000.000.00 0.000.00

0.00

Conclusions

• Prudent planners advised to work basis that availability of SBS polymers will remain tight for the immediate future

• Majority of butadiene produced used in tires

• Not possible to use unmodified asphalt for modified asphalt mixes.

Conclusions

• MSCR test developed specifically to discriminate between modified binders.

• Lab results indicate:– AR yielded highest percent recovery values

at both loading settings.– AR and SBS equally adept at withstanding

creep.– AR came the closest to replicating/

exceeding SBS binder properties

Conclusions

• Clear differences can be seen between the various types of modified asphalts in the creep recovery curve

• AR exhibited the least creep, while also demonstrating a very high recovery rate

• AR tended to yield the highest percent recoveries over the range of temperatures

Conclusions

• AR can be considered valid alternative to SBS from performance perspective.

• MSCR testing confirms elasticity of AR binder.

Thank you