1. Selecting the Correct PG Asphalt for Your Airport Project
A Driving Force In Asphalt
29th Annual FAA Airports Conference
Hershey, PA
March 2, 2006
Ronald Corun
CITGO Asphalt Technical Support Manager
CITGO Petroleum Corporation

2. What is SUPERPAVE? New Asphalt Binder specification
New Mix Design procedure using a new laboratory compaction device

3. We Have Three Asphalt Binders
Q. How do we determine which asphalt binder is best for our project?
A. The asphalt binder that gives the best performance A B C

4. Performance ? Q. What areas of poor performance do we want to avoid ?
Or, in other words, how do our asphalt pavements fail ?

5. How do asphalt pavements fail ?

9. How Did We Measure Asphalt Properties Before the PG Grading System?
Penetration Grading
Viscosity Grading

10. Viscosity Penetration vacuum 0 sec 5 sec penetration 100 g 100 g 25° C

11. Problem with one temperature grading

12. Problem with one temperature grading
According to the Penetration system:
According to the Viscosity System:

13. Asphalt binders
Q. Are the properties of asphalt binders constant over a pavements performance life?
A. NO! An asphalt binder’s response to loading is a function of three factors. . .
Age
Temperature
Rate of Loading

14. Asphalt binder’s response to loading is a function of. . .
1. age

15. Aging
Asphalt binders undergo aging through the loss of volatiles (a.k.a. loss of light ends) and oxidation.
From the standpoint of determining an asphalt binder's performance there are three key ages we need to address.

16. Key Aging New material - no aging During construction
Aging in the plant
Aging during placement
Late in the pavement's life
years of service

17. Aging - How ?
Early: To simulate the aging that occurs due to construction and initial service, we are going to employ the Rolling Thin-Film Oven (RTFO). This is a standard AASHTO test method, T 240.
Spec.: 85 minutes, 163°C, 400 ml of air per minute, 15 rpm

18. Rolling Thin Film Oven
163°C
controls
fan
bottle carriage
air jet

20. Rolling Thin Film Oven Sample Bottles
Clean Bottle
Before Loading
After Loading
Coated Bottle
After Testing

21. Aging - How ?
Long term: To simulate the aging that occurs due to oxidation over a pavement's life, we are going to subject the RTFO residue to time, temperature, and pressure. For this we are going to develop a pressure aging vessel, (PAV).

22. Aging - How ? Long term, Spec.: AASHTO PP1.
According to PP1, our RTFO residue is subjected to:
Temperature: 90 to 110°C
Time: hours
Pressure: kPa

23. Pressure Aging Vessel asphalt sample pan sample rack pressure vessel
air
pressure
temperature
probe

25. Asphalt binder’s response to loading is a function of. . .
1. age
2. temperature

26. Pavement Temperature, C
Pavement Temperature, C

27. Temperatures Q. What temperatures do we need to address ?
1. Rutting occurs at. . .
2. Fatigue Cracking occurs at. . .
3. Low Temperature Cracking occurs at. . .

28. Temperatures 1. Rutting occurs at high pavement temperatures, T(high)
2. Fatigue Cracking occurs at intermediate pavement temperatures, T(inter), and
3. Low Temperature Cracking occurs at low pavement temperatures, T(low).

29. Performance Grade Increments

30. Superpave Asphalt Binder Specification
Grading System Based on Climate
PG 64-22
Performance
Grade
Average 7-day
max pavement
design temp
Min pavement
design temp

31. Pavement Age Low Temp Fatigue Cracking Cracking Construction Rutting
[DTT]
[RV]
[DSR]
[BBR]
Pavement Age
RTFO - aging
No aging
PAV - aging

32. Dynamic Shear Rheometer, DSR
Apply a oscillating shear stress
Measure strain
A materials modulus is
Modulus = Stress / Strain
A measure of material stiffness

33. Dynamic Shear Rheometer, DSR

34. Dynamic Shear Rheometer, DSR

40. DSR provides G* and  G*, Complex Shear Modulus  , Phase Angle
G* / sin 
Correlates to rutting resistance.
G* sin 
Correlates to fatigue resistance.

41. Rutting Specification - Minimum Stiffness @ T(high)
G* / sin  > 1.00 kPa on unaged binder
G* / sin  > 2.20 kPa on RTFO aged binder

42. Pavement Age Low Temp Fatigue Cracking Cracking Construction Rutting
[DTT]
[RV]
[DSR]
[BBR]
Pavement Age
RTFO - aging
No aging
PAV - aging

43. Fatigue Cracking Specification - Maximum Stiffness @ T(inter)
G* sin  < 5000 kPa on PAV aged binder

44. Pavement Age Low Temp Fatigue Cracking Cracking Construction Rutting
[DTT]
[RV]
[DSR]
[BBR]
Pavement Age
RTFO - aging
No aging
PAV - aging

45. Superpave Binder Specification Low Temperature Characterization
The Bending Beam Rheometer (BBR) determines the Creep Stiffness (S) of an asphalt binder at low temperatures.
If a binder is too stiff at service temperatures, you can expect low temperature cracking.

46. Bending Beam Rheometer, BBR
Deflection Transducer
Air Bearing
Fluid
Bath
Control and
Data Acquisition
Load Cell
Asphalt Beam
Thermometer
Loading
Frame
Supports

48. Bending Beam Rheometer, BBR
binder specimen in mold
aluminum mold
rubber O-rings
12.7 mm
acetate
strips
125 mm
6.35 mm

52. Bending Beam Rheometer, BBR
980 mN (100 g) Load
Asphalt Beam
Deflected Position
Original Position

54. Bending Beam Rheometer, BBR
Time
Test Load
Deflection
Time

55. Bending Beam Rheometer, BBR
Deflection
(t)
simulates stiffness after
2 hours at 10 °C lower temp
60 sec
Time

56. BBR Data - Relaxation slope = m-value 60 sec Log Creep Stiffness, S
PG Spec
slope = m-value
Log Loading Time
60 sec

57. Low Temperature Cracking Specification
Maximum Creep Stiffness Value (S)
S < 300 MPa
Minimum m-value
m > 0.300

58. Other PG Binder Tests . . . Q. What about Construct-ability ?
A. A better word might be Pump-ability. A concern raised during SHRP was the need to address modified systems. Heavily modified systems can literally burn-out pumps. To address this, we will use ASTM D 4404, "Brookfield Rotational Viscometer."

59. Pavement Age Low Temp Fatigue Cracking Cracking Construction Rutting
[DTT]
[RV]
[DSR]
[BBR]
Pavement Age
RTFO - aging
No aging
PAV - aging

60. Rotational Viscometer
applied torque
from motor
spindle
asphalt sample
sample chamber

61. Rotational Viscometer
digital
readout
Brookfield
viscometer
control
keys
spindle extension
temperature
controller
thermo -
container
(ThermoselTM)

62. Rotational Viscometer

63. Rotational Viscometer Specification
135ºC < 3.0 Pa-s
Run viscosity at both 135ºC and 165ºC to determine laboratory mixing and compaction temperatures

64. Lab Mixing & Compaction Temperatures
Viscosity, Pa s 10 5 1 .5 .3
Compaction Range .2
Mixing Range .1
100
110
120
130
140
150
160
170
180
190
200
Temperature, C

65. Asphalt binder’s response to loading is a function of. . .
1. age
2. temperature
3. rate of loading

66. Time vs. Temperature
1 hour
60 C
1 hour
10 hours
25 C

67. Effect of Traffic Speed on Binder Stiffness
PG Spec
2.2 kPa

70. FHWA ALF Binder Study Rut Depth @ 5000 passes of ALF 11 mph @ 58ºC
30 mm
24 mm
Rut Depth, mm
4 mm
Asphalt Binder Grade

71. Effect of Loading Rate on Binder Selection
Example
for 55 mph highway PG 64-22
for 30 mph highway PG 70-22
for intersections PG 76-22
Standard Grade
Slow - Bump
one grade
Stopped - Bump
one grade

72. SUPERPAVE Asphalt Binder Specification
Selection is based on
Climate
Traffic speed
Amount of traffic - measured in ESALs
PG grade
Asphalt content of mix - durability

73. Is the PG Binder Modified ?
“Rule of 92”
PG = = 92
Binder may be modified!!
PG = = 98
Binder will be modified !!
(Depends on Asphalt Source!)

74. Asphalt Modifiers Change effects of temperature on physical properties
Reduce effects of aging/oxidation
Improve adhesion to aggregates

75. Modification Concept Viscosity Temperature “Hard” asphalt
“Ideal” Asphalt
Semi-solid
Viscosity
“Soft” asphalt
Fluid
Service
Comp Mix
Temperature

76. Modifiers that affect consistency:
Asphalt Modifiers
Modifiers that affect consistency:
Natural Asphalts (TLA)
Chemicals
Oxidants
Fibers
Polymers

77. Polymers From Greek: “many parts”
High molecular weight molecules formed from combining simpler molecules/chemical compounds
Styrene- Butadiene-Styrene (SBS) is most widely used polymer in asphalt

78. What is SBS? S S S S S B B B POLY-STYRENE POLY-BUTADIENE Disposable
fork B B
POLY-BUTADIENE B
Rubber
band

79. What is SBS? B S S
LINEAR SBS B S S
RADIAL SBS B S

80. What is SBS? Styrene-Butadiene-Styrene
Styrene provides stiffness at high temperatures
Butadiene gives flexibility at low temperatures
Complete dispersion of SBS in asphalt provides best performance

81. How is PMA Produced? Start with PG 64-22 Test Asphalt Properties
Dissolve and Cross-link SBS Molecules
Reaction Time
Constant Agitation
Constant Heat
Test Asphalt Properties
Performance Properties
Homogenous Material
Consistency

82. SBS in Asphalt - Beginning

83. SBS Intermediate Curing

84. Finished SBS Modified Asphalt

85. Superpave Plus Binder Specifications
Used to ensure polymer-modification
Example: PG Plus Maximum phase angle of 75 degrees
Test methods
DSR Phase Angle (Engineering value)
Amount of Stretch and/or Recovery (Empirical)

86. Elastic Recovery 2 1
Neat doesn’t recover
Modified recovers 3 4

87. PG Binder Selection for Airports
How do we get from ESALs to Airplanes?
Airfield Asphalt Pavement Technology Program (AAPTP)
Research funded by AIR-21
Managed by Auburn University
Primarily will research adapting Superpave to airfields
Until research is complete – common sense guidelines developed by FAA and DOD

88. FAA and DoD General Guidelines for Binder Grade Selection on Airfields
Consult with local DOT
Determine grades that are typically being used and are available for the particular area
Determine the “Standard Grade”
Typically used for highways with less than 10 million ESALs
Sufficient on most GA airports
Consider ‘Bumping’ for top 5 inches if concerned
Past performance?
High tire pressures?
Standing or slow traffic (stacking on TWs)?
Channelized traffic (alleyways)?

89. Grade Bumping Example - Airfields
For Aircraft < 12,500 lbs PG 64-22
For Aircraft < 100,000 lbs PG or PG 76-22
For Aircraft > 100,000 lbs PG or PG 82-22
Need to Consider Traffic Flow

90. The higher the Grade, the stiffer the binder. The more rut resistance.
Rule # 1
PG 82
PG 76
PG 70
PG 64
PG 58
The higher the
Grade, the stiffer
the binder.
The more rut
resistance.

91. The lower the number, the more resistant to thermal cracking.
Rule # 2
PG - 22
- 28
-34
The lower the
number, the more
resistant to
thermal cracking.

92. The greater the difference
Rule # 3
PG 82O 22O
PG 76O 22O
PG 70O 22O
PG 64O 28O
PG 64O 22O
PG 58O 28O
104O
98O
92O
86O
Mix Cost %
Mix Cost %
The greater the difference
the higher the cost.

93. CONCLUSIONS
Training needed for everyone if SUPERPAVE is to be used successfully
PG Grade System provides the right asphalt for varying climate and traffic conditions
SUPERPAVE places more tools in the Pavement Designers’ Tool Box
Designers can solve pavement problems they were unable to in the past using SUPERPAVE
SUPERPAVE

94. Questions?