Performance Tests of Asphalt Mixtures

Louay N. Mohammad, Ph.D.Department of Civil and Environmental Engineering

LA Transportation Research  CenterLouisiana State University

42nd Annual Rocky Mountain Asphalt Conference 

February 25 – 27, 2015Denver, Colorado

My Story• Baxkground• Asphalt Mixture Design• Review performance Tests

– High Temperature– Intermediate Temperature

• Mixture Design– Volumetric– Mechanistic

• Summary

Background• Asphalt cement• Aggregate

– Coarse– Fine 

• Increased use of Reclaimed Materials– RAP / RAS– Waste tires– Industrial waste

Background• Practice of utilizing RAP and/or RAS in new asphalt mixtures has increased in

recent years– economic and environmental benefits

• RAP has most widely used materials – Wearing Course: 15%– Binder Course: 20%– Base Course: 30%

• RAS has emerged as a material of interest to the paving community• RAP and/or RAS valuable components in asphalt mixtures

– With increased demand and limited supply of aggregate and binder• Potential benefits are high on use high percentages of RAP

– state agencies have not proceeded to use high percentages of RAP on their roadways

– non-uniformity of RAP materials– agency’s lack of confidence in the long term performance data and specifications.– problem is further augmented when RAS is used in conjunction with RAP

Objectives of Mixture Design• Perform

– permanent deformation– fatigue cracking – repeated load– low temperature cracking – moisture induced damage

• Safety– Resist skid

• Constructable– Workability

Typical Asphalt Mixture Design• Volumetrics

– Voids in the Total Mix, VTM– Voids in the Mineral Aggregate, VMA– Voids Filled with Asphalt, VFA

• Densification– Stages during lab compaction process

VOLUME MASS

air

asphalt

aggregate

TotalMass

TotalVolume

aggregate

Current Volumetric mix design • Ensure satisfactory performance

– strict material specifications requirement

– volumetric mix criteria

• No mechanical “proof” test – Marshall mix design

• Limited Mechanical tests– mix verification

• intermediate and high volume traffic 

– Superpave Shear Tester  (SST)

• Not widely used 

Overall Relative Rut Susceptibility Ranking

0

1

2

3

LA 4 BC LA 22 BC LA 22 WC LA 121 BC LA 121 WC LA 353 BC/WC

Rel

ativ

e R

ut S

usce

ptib

ility

Excellent

Good

Fair

25 mm19 mm

Laboratory Performance Assessments

Mixture DesignBinder ContentBinder QualityAggregates

Selection of Mechanical Tests• Laboratory Tests 

– Pavement Performance• High Temperature

– Permanent deformation

• Intermediate Temperature – Fracture/Fatigue 

• Low Temperature – Low temp cracking

• Features to be considered– Measure/relate to fundamental properties– Simple, repeatable, easily‐calibrated, – quick, not requiring highly‐trained personnel, – Can utilize low‐cost equipment.  – Sensitive to subtle changes in mixture properties

Laboratory Performance Tests

Louisiana Balanced Asphalt Mixture Design• High temperature Performance

• Loaded Wheel Tracking Test• Relation to FN

• Rutting• Intermediate temperature Performance

• Semi Circular Bend Test• Cracking

• Low temperature performance• TSRST

SCB Test at Intermediate Temperature• Fracture Mechanics Approach• Analytical method to calculate the driving force on a crack • characterize the material's resistance to fracture• Cracks• Initiates

– Small cracks 

• Propagates– Large crack– Caused by tensile stresses– analyzed by fracture mechanics models

Advantages of SCB Test• Utilize laboratory SGC specimens or field cores• multiple specimens can be obtained from one core 

– reducing the error caused by heterogeneities among samples

• Test setup is simple• Testing time is around 10 minutes per specimen• Ease of sample preparation• Stress field resembles pure tensile conditions

Draft Standard Test Method• Developed • Circulated

Test Equipment ‐‐ Development

Test simplicity – technician training requirements

» Minimal» Several labs (state DOTs, Univ., testing labs)

– time for preparing samples» Compact, Cut, and preform volumetric measurements » 1 day for the set (4 specimens)

– testing specimens» 1 day for the set (2 samples = 4 specimens)

– analyzing data» Spreadsheet: 30 minutes

LWT Test at High Temperature

Test simplicity – technician training requirements

» Minimal» Several labs (state DOTs, Univ., testing labs)

– time for preparing samples» Compact, Cut, and Notch, preform volumetric measurements » 1 day for the set (12 test specimens)

– testing specimens» 1- 2 hours for the set (12 test specimens)

– analyzing data» Spreadsheet with cut/paste: 15 minutes

SCB test at Intermediate Temperature

Results

02468

101214161820

64CO 70CO‐M 76CO‐M 76CRM 76RAP15

10.2

5.6 5.34.6

5.7

Rut D

epth, 20K

 passes, m

m

Binder Type

2011 AAPT: Laboratory Evaluation of Asphalt Mixtures Containing Sustainable Technologies

LWT Test Results ‐‐ 50°C, WetSBS, CRM

Semi‐Circular Bend Test Results, 25°CSBS, CRM

00.10.20.30.40.50.60.70.80.91

64CO 70CO‐M 76CO‐M 76CRM

Jc, K

j/m2

Binder Type

2011 AAPT: Laboratory Evaluation of Asphalt Mixtures Containing Sustainable Technologies

0

2

4

6

8

10

12

14

16

18

20

6422CO 6422GR 7022CO 7016GR 7022GR 7622CO 7622GR

Rut

Dep

th @

20,

000

pass

es (m

m)

Mixture ID

PG 64-22 PG 70-22 PG 76-22

2013 TRB: Laboratory Evaluation of Asphalt Mixtures Containing Bio‐Binder Technologies

LWT Test Results, 50°C, WetBio‐Binders

2013 TRB: Laboratory Evaluation of Asphalt Mixtures Containing Bio‐Binder Technologies

0

2

4

6

8

10

12

14

16

18

20

6422CO 6422GR 7022CO 7016GR 7022GR 7622CO 7622GR

Rut

Dep

th @

20,

000

pass

es (m

m)

Mixture ID

PG 64-22 PG 70-22 PG 76-22

LWT Test Results, 50°C, WetBio‐Binders

Semi‐Circular Bend Test Results, 25°CBio‐Binders

2013 TRB: Laboratory Evaluation of Asphalt Mixtures Containing Bio‐Binder Technologies

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

6422CO 6422GR 7022CO 7016GR 7022GR 7622CO 7622GR

Jc (K

j/m2 )

Mixture ID

PG 64-22 PG 70-22 PG 76-22

A

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

Mix 1No RAP/RAS

Mix 2‐B5RAS

Mix 3‐B5RAS

Mix 4‐B5RAS

Mix 5‐B5RAS

Mix 6‐B15RAP+5RAS

Rut D

epth, 20K

 Passes, m

m

Mixture type

Loaded Wheel Tracking Test Results, 50°CRAP and/or RAS 

No Recycling Agents Recycling Agents

Mix 1 = 70COMix 2 = 70PG5PMix 3 = 52PG5P‐RA 1Mix 4 = 70PG5P‐RA 2Mix 5 = 70PG5P‐RA 3Mix 6 = 70PG5P15RAP‐RA 2

RA 1 RA 2 RA 3 RA 2

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Mix 1No RAP/RAS

Mix 2‐B5RAS

Mix 3‐B5RAS

Mix 4‐B5RAS

Mix 5‐B5RAS

Mix 6‐B15RAP+5RAS

J c, KJ/m

2

Mixture type

RBR  = 0 %

RBR  = 9.4 %

Recycling Agents

Semi‐Circular Bend Test Results, 25°CRAP and/or RAS

No Recycling Agents

RBR  = 22.6 %

RBR  = 13.2 %

RBR  = 26.4 %

RBR = 41.5%

Mix 1 = 70COMix 2 = 70PG5PMix 3 = 52PG5P‐RA 1Mix 4 = 70PG5P‐RA 2Mix 5 = 70PG5P‐RA 3Mix 6 = 70PG5P15RAP‐RA 2

RA 1 RA 2 RA 3 RA 2

LWT Test Results, 50°C

Level 1

Level 2

90%

Semi‐Circular Bend Test Results, 25°C

Louisiana Balanced Mixture Design• Volumetric and Performance Mixture Testing  

– Rutting                LWT test  (50°C, Wet)– Cracking              SCB test (25°C)

00.20.40.60.81

1.21.41.6

0 5 10 15 20

Cracking

 Resistance

Rutting Resistance

Volumetric Parameters

Cracking Performance

High Temperature Performance

2013 Proposed Specification

2013 Proposed Specification

2014 TRB: Balanced Asphalt Mixture Design through Specification Modification: Louisiana’s Experience

Property 2006 Specifications

2013 Proposed Specifications 

Ndesign, Gyrations

75 – 100 65 – 75a

Minimum VMA, %

10 – 13 10.5 – 13.0 

VFA, % 68 – 78 69 – 80Air Voids, % 2.5 – 4.5 2.5 – 4.5 

0

5

10

15

20

0 5 10 15 20 25 30 35 40 45 50 55

Rut D

epth, m

m

Mixture Number

PG 64‐22 PG 70‐22M PG 76‐22M PG 82‐22CRM

LWT Test Results, 50°C

0

5

10

15

20

0 5 10 15 20 25 30 35 40 45 50 55

Rut D

epth, m

m

Mixture Number

PG 64‐22 PG 70‐22M PG 76‐22M PG 82‐22CRM

LWT Test Results, 50°C

0

0.5

1

1.5

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64

Jc, K

J/m

2

Mixture Number

PG 64‐22 PG 70‐22M PG 76‐22M PG 82‐22CRM

SCB test Results, 25°C

0

0.5

1

1.5

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64

Jc, K

J/m

2

Mixture Number

PG 64‐22 PG 70‐22M PG 76‐22M PG 82‐22CRM

SCB test Results, 25°C

0.0

4.0

8.0

12.0

16.0

20.0

PG 64‐22 PG 70‐22 M PG 76‐22 M PG 82‐22rm

Rut D

epth, 20K

 passes, m

m

Binder Type

19‐mm LS

LWT Test Results, 50°C

0.0

0.2

0.4

0.6

0.8

PG 64‐22 PG 70‐22 M PG 76‐22 M

Jc, K

j/m2

Binder Type

19‐mm LS

Semi‐Circular Bend Test Results, 25°C

Development Of Performance Based Specifications For Louisiana Asphalt Mixtures Laboratory and Field evaluation of 10 projects

– Projects in service for 3 – 10 years. – Does SCB parameter translate to field performance?

60.00

65.00

70.00

75.00

80.00

85.00

90.00

95.00

100.00

105.00

0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

LAD

OTD

PM

S C

rack

ing

Inde

x

Laboratory Measured Jc, kJ/mm2

Y = 100 – (0.969+0.036X) -170)

r2 : 0.73

Selection of a Criteria

60.00

65.00

70.00

75.00

80.00

85.00

90.00

95.00

100.00

105.00

0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

LAD

OTD

PM

S C

rack

ing

Inde

x

Laboratory Measured Jc, kJ/mm2

Y = 100 – (0.969+0.036X) -170)

r2 : 0.73

High Traffic PMS Trigger

Low Traffic PMS Trigger

Implementation ‐‐ LADOTD

SCB, min, Jc, kJ/m2 @ 25⁰ C, Aged

All mix design level 1 must meet minimum 0.5 Jc ,All mix design level 2 must meet minimum 0.6 Jc.

Summary• Volumetric-based design

– Not sufficient• Compliment Volumetric design

– Mechanistic tests– Criteria– Performance related

• Incremental/Evaluate– Specifications

• Loaded Wheel Tester Test– High Temperature

• Semi-Circular Bend Test – Intermediate temperature – Cracking performance– Jc was sensitive to mixture parameters considered

• Further validation with more field and laboratory data

THANK

YOU