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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